Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4676 insertions, 0 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
new file mode 100644
index 0000000000..03c10e0ba0
--- /dev/null
+++ b/fs/btrfs/extent_io.c
@@ -0,0 +1,4676 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bitops.h>
+#include <linux/slab.h>
+#include <linux/bio.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/page-flags.h>
+#include <linux/sched/mm.h>
+#include <linux/spinlock.h>
+#include <linux/blkdev.h>
+#include <linux/swap.h>
+#include <linux/writeback.h>
+#include <linux/pagevec.h>
+#include <linux/prefetch.h>
+#include <linux/fsverity.h>
+#include "misc.h"
+#include "extent_io.h"
+#include "extent-io-tree.h"
+#include "extent_map.h"
+#include "ctree.h"
+#include "btrfs_inode.h"
+#include "bio.h"
+#include "check-integrity.h"
+#include "locking.h"
+#include "rcu-string.h"
+#include "backref.h"
+#include "disk-io.h"
+#include "subpage.h"
+#include "zoned.h"
+#include "block-group.h"
+#include "compression.h"
+#include "fs.h"
+#include "accessors.h"
+#include "file-item.h"
+#include "file.h"
+#include "dev-replace.h"
+#include "super.h"
+#include "transaction.h"
+
+static struct kmem_cache *extent_buffer_cache;
+
+#ifdef CONFIG_BTRFS_DEBUG
+static inline void btrfs_leak_debug_add_eb(struct extent_buffer *eb)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	unsigned long flags;
+
+	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
+	list_add(&eb->leak_list, &fs_info->allocated_ebs);
+	spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
+}
+
+static inline void btrfs_leak_debug_del_eb(struct extent_buffer *eb)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	unsigned long flags;
+
+	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
+	list_del(&eb->leak_list);
+	spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
+}
+
+void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info)
+{
+	struct extent_buffer *eb;
+	unsigned long flags;
+
+	/*
+	 * If we didn't get into open_ctree our allocated_ebs will not be
+	 * initialized, so just skip this.
+	 */
+	if (!fs_info->allocated_ebs.next)
+		return;
+
+	WARN_ON(!list_empty(&fs_info->allocated_ebs));
+	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
+	while (!list_empty(&fs_info->allocated_ebs)) {
+		eb = list_first_entry(&fs_info->allocated_ebs,
+				      struct extent_buffer, leak_list);
+		pr_err(
+	"BTRFS: buffer leak start %llu len %lu refs %d bflags %lu owner %llu\n",
+		       eb->start, eb->len, atomic_read(&eb->refs), eb->bflags,
+		       btrfs_header_owner(eb));
+		list_del(&eb->leak_list);
+		kmem_cache_free(extent_buffer_cache, eb);
+	}
+	spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
+}
+#else
+#define btrfs_leak_debug_add_eb(eb)			do {} while (0)
+#define btrfs_leak_debug_del_eb(eb)			do {} while (0)
+#endif
+
+/*
+ * Structure to record info about the bio being assembled, and other info like
+ * how many bytes are there before stripe/ordered extent boundary.
+ */
+struct btrfs_bio_ctrl {
+	struct btrfs_bio *bbio;
+	enum btrfs_compression_type compress_type;
+	u32 len_to_oe_boundary;
+	blk_opf_t opf;
+	btrfs_bio_end_io_t end_io_func;
+	struct writeback_control *wbc;
+};
+
+static void submit_one_bio(struct btrfs_bio_ctrl *bio_ctrl)
+{
+	struct btrfs_bio *bbio = bio_ctrl->bbio;
+
+	if (!bbio)
+		return;
+
+	/* Caller should ensure the bio has at least some range added */
+	ASSERT(bbio->bio.bi_iter.bi_size);
+
+	if (btrfs_op(&bbio->bio) == BTRFS_MAP_READ &&
+	    bio_ctrl->compress_type != BTRFS_COMPRESS_NONE)
+		btrfs_submit_compressed_read(bbio);
+	else
+		btrfs_submit_bio(bbio, 0);
+
+	/* The bbio is owned by the end_io handler now */
+	bio_ctrl->bbio = NULL;
+}
+
+/*
+ * Submit or fail the current bio in the bio_ctrl structure.
+ */
+static void submit_write_bio(struct btrfs_bio_ctrl *bio_ctrl, int ret)
+{
+	struct btrfs_bio *bbio = bio_ctrl->bbio;
+
+	if (!bbio)
+		return;
+
+	if (ret) {
+		ASSERT(ret < 0);
+		btrfs_bio_end_io(bbio, errno_to_blk_status(ret));
+		/* The bio is owned by the end_io handler now */
+		bio_ctrl->bbio = NULL;
+	} else {
+		submit_one_bio(bio_ctrl);
+	}
+}
+
+int __init extent_buffer_init_cachep(void)
+{
+	extent_buffer_cache = kmem_cache_create("btrfs_extent_buffer",
+			sizeof(struct extent_buffer), 0,
+			SLAB_MEM_SPREAD, NULL);
+	if (!extent_buffer_cache)
+		return -ENOMEM;
+
+	return 0;
+}
+
+void __cold extent_buffer_free_cachep(void)
+{
+	/*
+	 * Make sure all delayed rcu free are flushed before we
+	 * destroy caches.
+	 */
+	rcu_barrier();
+	kmem_cache_destroy(extent_buffer_cache);
+}
+
+void extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end)
+{
+	unsigned long index = start >> PAGE_SHIFT;
+	unsigned long end_index = end >> PAGE_SHIFT;
+	struct page *page;
+
+	while (index <= end_index) {
+		page = find_get_page(inode->i_mapping, index);
+		BUG_ON(!page); /* Pages should be in the extent_io_tree */
+		clear_page_dirty_for_io(page);
+		put_page(page);
+		index++;
+	}
+}
+
+static void process_one_page(struct btrfs_fs_info *fs_info,
+			     struct page *page, struct page *locked_page,
+			     unsigned long page_ops, u64 start, u64 end)
+{
+	u32 len;
+
+	ASSERT(end + 1 - start != 0 && end + 1 - start < U32_MAX);
+	len = end + 1 - start;
+
+	if (page_ops & PAGE_SET_ORDERED)
+		btrfs_page_clamp_set_ordered(fs_info, page, start, len);
+	if (page_ops & PAGE_START_WRITEBACK) {
+		btrfs_page_clamp_clear_dirty(fs_info, page, start, len);
+		btrfs_page_clamp_set_writeback(fs_info, page, start, len);
+	}
+	if (page_ops & PAGE_END_WRITEBACK)
+		btrfs_page_clamp_clear_writeback(fs_info, page, start, len);
+
+	if (page != locked_page && (page_ops & PAGE_UNLOCK))
+		btrfs_page_end_writer_lock(fs_info, page, start, len);
+}
+
+static void __process_pages_contig(struct address_space *mapping,
+				   struct page *locked_page, u64 start, u64 end,
+				   unsigned long page_ops)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(mapping->host->i_sb);
+	pgoff_t start_index = start >> PAGE_SHIFT;
+	pgoff_t end_index = end >> PAGE_SHIFT;
+	pgoff_t index = start_index;
+	struct folio_batch fbatch;
+	int i;
+
+	folio_batch_init(&fbatch);
+	while (index <= end_index) {
+		int found_folios;
+
+		found_folios = filemap_get_folios_contig(mapping, &index,
+				end_index, &fbatch);
+		for (i = 0; i < found_folios; i++) {
+			struct folio *folio = fbatch.folios[i];
+
+			process_one_page(fs_info, &folio->page, locked_page,
+					 page_ops, start, end);
+		}
+		folio_batch_release(&fbatch);
+		cond_resched();
+	}
+}
+
+static noinline void __unlock_for_delalloc(struct inode *inode,
+					   struct page *locked_page,
+					   u64 start, u64 end)
+{
+	unsigned long index = start >> PAGE_SHIFT;
+	unsigned long end_index = end >> PAGE_SHIFT;
+
+	ASSERT(locked_page);
+	if (index == locked_page->index && end_index == index)
+		return;
+
+	__process_pages_contig(inode->i_mapping, locked_page, start, end,
+			       PAGE_UNLOCK);
+}
+
+static noinline int lock_delalloc_pages(struct inode *inode,
+					struct page *locked_page,
+					u64 start,
+					u64 end)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	struct address_space *mapping = inode->i_mapping;
+	pgoff_t start_index = start >> PAGE_SHIFT;
+	pgoff_t end_index = end >> PAGE_SHIFT;
+	pgoff_t index = start_index;
+	u64 processed_end = start;
+	struct folio_batch fbatch;
+
+	if (index == locked_page->index && index == end_index)
+		return 0;
+
+	folio_batch_init(&fbatch);
+	while (index <= end_index) {
+		unsigned int found_folios, i;
+
+		found_folios = filemap_get_folios_contig(mapping, &index,
+				end_index, &fbatch);
+		if (found_folios == 0)
+			goto out;
+
+		for (i = 0; i < found_folios; i++) {
+			struct page *page = &fbatch.folios[i]->page;
+			u32 len = end + 1 - start;
+
+			if (page == locked_page)
+				continue;
+
+			if (btrfs_page_start_writer_lock(fs_info, page, start,
+							 len))
+				goto out;
+
+			if (!PageDirty(page) || page->mapping != mapping) {
+				btrfs_page_end_writer_lock(fs_info, page, start,
+							   len);
+				goto out;
+			}
+
+			processed_end = page_offset(page) + PAGE_SIZE - 1;
+		}
+		folio_batch_release(&fbatch);
+		cond_resched();
+	}
+
+	return 0;
+out:
+	folio_batch_release(&fbatch);
+	if (processed_end > start)
+		__unlock_for_delalloc(inode, locked_page, start, processed_end);
+	return -EAGAIN;
+}
+
+/*
+ * Find and lock a contiguous range of bytes in the file marked as delalloc, no
+ * more than @max_bytes.
+ *
+ * @start:	The original start bytenr to search.
+ *		Will store the extent range start bytenr.
+ * @end:	The original end bytenr of the search range
+ *		Will store the extent range end bytenr.
+ *
+ * Return true if we find a delalloc range which starts inside the original
+ * range, and @start/@end will store the delalloc range start/end.
+ *
+ * Return false if we can't find any delalloc range which starts inside the
+ * original range, and @start/@end will be the non-delalloc range start/end.
+ */
+EXPORT_FOR_TESTS
+noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
+				    struct page *locked_page, u64 *start,
+				    u64 *end)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
+	const u64 orig_start = *start;
+	const u64 orig_end = *end;
+	/* The sanity tests may not set a valid fs_info. */
+	u64 max_bytes = fs_info ? fs_info->max_extent_size : BTRFS_MAX_EXTENT_SIZE;
+	u64 delalloc_start;
+	u64 delalloc_end;
+	bool found;
+	struct extent_state *cached_state = NULL;
+	int ret;
+	int loops = 0;
+
+	/* Caller should pass a valid @end to indicate the search range end */
+	ASSERT(orig_end > orig_start);
+
+	/* The range should at least cover part of the page */
+	ASSERT(!(orig_start >= page_offset(locked_page) + PAGE_SIZE ||
+		 orig_end <= page_offset(locked_page)));
+again:
+	/* step one, find a bunch of delalloc bytes starting at start */
+	delalloc_start = *start;
+	delalloc_end = 0;
+	found = btrfs_find_delalloc_range(tree, &delalloc_start, &delalloc_end,
+					  max_bytes, &cached_state);
+	if (!found || delalloc_end <= *start || delalloc_start > orig_end) {
+		*start = delalloc_start;
+
+		/* @delalloc_end can be -1, never go beyond @orig_end */
+		*end = min(delalloc_end, orig_end);
+		free_extent_state(cached_state);
+		return false;
+	}
+
+	/*
+	 * start comes from the offset of locked_page.  We have to lock
+	 * pages in order, so we can't process delalloc bytes before
+	 * locked_page
+	 */
+	if (delalloc_start < *start)
+		delalloc_start = *start;
+
+	/*
+	 * make sure to limit the number of pages we try to lock down
+	 */
+	if (delalloc_end + 1 - delalloc_start > max_bytes)
+		delalloc_end = delalloc_start + max_bytes - 1;
+
+	/* step two, lock all the pages after the page that has start */
+	ret = lock_delalloc_pages(inode, locked_page,
+				  delalloc_start, delalloc_end);
+	ASSERT(!ret || ret == -EAGAIN);
+	if (ret == -EAGAIN) {
+		/* some of the pages are gone, lets avoid looping by
+		 * shortening the size of the delalloc range we're searching
+		 */
+		free_extent_state(cached_state);
+		cached_state = NULL;
+		if (!loops) {
+			max_bytes = PAGE_SIZE;
+			loops = 1;
+			goto again;
+		} else {
+			found = false;
+			goto out_failed;
+		}
+	}
+
+	/* step three, lock the state bits for the whole range */
+	lock_extent(tree, delalloc_start, delalloc_end, &cached_state);
+
+	/* then test to make sure it is all still delalloc */
+	ret = test_range_bit(tree, delalloc_start, delalloc_end,
+			     EXTENT_DELALLOC, 1, cached_state);
+	if (!ret) {
+		unlock_extent(tree, delalloc_start, delalloc_end,
+			      &cached_state);
+		__unlock_for_delalloc(inode, locked_page,
+			      delalloc_start, delalloc_end);
+		cond_resched();
+		goto again;
+	}
+	free_extent_state(cached_state);
+	*start = delalloc_start;
+	*end = delalloc_end;
+out_failed:
+	return found;
+}
+
+void extent_clear_unlock_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
+				  struct page *locked_page,
+				  u32 clear_bits, unsigned long page_ops)
+{
+	clear_extent_bit(&inode->io_tree, start, end, clear_bits, NULL);
+
+	__process_pages_contig(inode->vfs_inode.i_mapping, locked_page,
+			       start, end, page_ops);
+}
+
+static bool btrfs_verify_page(struct page *page, u64 start)
+{
+	if (!fsverity_active(page->mapping->host) ||
+	    PageUptodate(page) ||
+	    start >= i_size_read(page->mapping->host))
+		return true;
+	return fsverity_verify_page(page);
+}
+
+static void end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+
+	ASSERT(page_offset(page) <= start &&
+	       start + len <= page_offset(page) + PAGE_SIZE);
+
+	if (uptodate && btrfs_verify_page(page, start))
+		btrfs_page_set_uptodate(fs_info, page, start, len);
+	else
+		btrfs_page_clear_uptodate(fs_info, page, start, len);
+
+	if (!btrfs_is_subpage(fs_info, page))
+		unlock_page(page);
+	else
+		btrfs_subpage_end_reader(fs_info, page, start, len);
+}
+
+/*
+ * after a writepage IO is done, we need to:
+ * clear the uptodate bits on error
+ * clear the writeback bits in the extent tree for this IO
+ * end_page_writeback if the page has no more pending IO
+ *
+ * Scheduling is not allowed, so the extent state tree is expected
+ * to have one and only one object corresponding to this IO.
+ */
+static void end_bio_extent_writepage(struct btrfs_bio *bbio)
+{
+	struct bio *bio = &bbio->bio;
+	int error = blk_status_to_errno(bio->bi_status);
+	struct bio_vec *bvec;
+	struct bvec_iter_all iter_all;
+
+	ASSERT(!bio_flagged(bio, BIO_CLONED));
+	bio_for_each_segment_all(bvec, bio, iter_all) {
+		struct page *page = bvec->bv_page;
+		struct inode *inode = page->mapping->host;
+		struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+		const u32 sectorsize = fs_info->sectorsize;
+		u64 start = page_offset(page) + bvec->bv_offset;
+		u32 len = bvec->bv_len;
+
+		/* Our read/write should always be sector aligned. */
+		if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
+			btrfs_err(fs_info,
+		"partial page write in btrfs with offset %u and length %u",
+				  bvec->bv_offset, bvec->bv_len);
+		else if (!IS_ALIGNED(bvec->bv_len, sectorsize))
+			btrfs_info(fs_info,
+		"incomplete page write with offset %u and length %u",
+				   bvec->bv_offset, bvec->bv_len);
+
+		btrfs_finish_ordered_extent(bbio->ordered, page, start, len, !error);
+		if (error)
+			mapping_set_error(page->mapping, error);
+		btrfs_page_clear_writeback(fs_info, page, start, len);
+	}
+
+	bio_put(bio);
+}
+
+/*
+ * Record previously processed extent range
+ *
+ * For endio_readpage_release_extent() to handle a full extent range, reducing
+ * the extent io operations.
+ */
+struct processed_extent {
+	struct btrfs_inode *inode;
+	/* Start of the range in @inode */
+	u64 start;
+	/* End of the range in @inode */
+	u64 end;
+	bool uptodate;
+};
+
+/*
+ * Try to release processed extent range
+ *
+ * May not release the extent range right now if the current range is
+ * contiguous to processed extent.
+ *
+ * Will release processed extent when any of @inode, @uptodate, the range is
+ * no longer contiguous to the processed range.
+ *
+ * Passing @inode == NULL will force processed extent to be released.
+ */
+static void endio_readpage_release_extent(struct processed_extent *processed,
+			      struct btrfs_inode *inode, u64 start, u64 end,
+			      bool uptodate)
+{
+	struct extent_state *cached = NULL;
+	struct extent_io_tree *tree;
+
+	/* The first extent, initialize @processed */
+	if (!processed->inode)
+		goto update;
+
+	/*
+	 * Contiguous to processed extent, just uptodate the end.
+	 *
+	 * Several things to notice:
+	 *
+	 * - bio can be merged as long as on-disk bytenr is contiguous
+	 *   This means we can have page belonging to other inodes, thus need to
+	 *   check if the inode still matches.
+	 * - bvec can contain range beyond current page for multi-page bvec
+	 *   Thus we need to do processed->end + 1 >= start check
+	 */
+	if (processed->inode == inode && processed->uptodate == uptodate &&
+	    processed->end + 1 >= start && end >= processed->end) {
+		processed->end = end;
+		return;
+	}
+
+	tree = &processed->inode->io_tree;
+	/*
+	 * Now we don't have range contiguous to the processed range, release
+	 * the processed range now.
+	 */
+	unlock_extent(tree, processed->start, processed->end, &cached);
+
+update:
+	/* Update processed to current range */
+	processed->inode = inode;
+	processed->start = start;
+	processed->end = end;
+	processed->uptodate = uptodate;
+}
+
+static void begin_page_read(struct btrfs_fs_info *fs_info, struct page *page)
+{
+	ASSERT(PageLocked(page));
+	if (!btrfs_is_subpage(fs_info, page))
+		return;
+
+	ASSERT(PagePrivate(page));
+	btrfs_subpage_start_reader(fs_info, page, page_offset(page), PAGE_SIZE);
+}
+
+/*
+ * after a readpage IO is done, we need to:
+ * clear the uptodate bits on error
+ * set the uptodate bits if things worked
+ * set the page up to date if all extents in the tree are uptodate
+ * clear the lock bit in the extent tree
+ * unlock the page if there are no other extents locked for it
+ *
+ * Scheduling is not allowed, so the extent state tree is expected
+ * to have one and only one object corresponding to this IO.
+ */
+static void end_bio_extent_readpage(struct btrfs_bio *bbio)
+{
+	struct bio *bio = &bbio->bio;
+	struct bio_vec *bvec;
+	struct processed_extent processed = { 0 };
+	/*
+	 * The offset to the beginning of a bio, since one bio can never be
+	 * larger than UINT_MAX, u32 here is enough.
+	 */
+	u32 bio_offset = 0;
+	struct bvec_iter_all iter_all;
+
+	ASSERT(!bio_flagged(bio, BIO_CLONED));
+	bio_for_each_segment_all(bvec, bio, iter_all) {
+		bool uptodate = !bio->bi_status;
+		struct page *page = bvec->bv_page;
+		struct inode *inode = page->mapping->host;
+		struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+		const u32 sectorsize = fs_info->sectorsize;
+		u64 start;
+		u64 end;
+		u32 len;
+
+		btrfs_debug(fs_info,
+			"end_bio_extent_readpage: bi_sector=%llu, err=%d, mirror=%u",
+			bio->bi_iter.bi_sector, bio->bi_status,
+			bbio->mirror_num);
+
+		/*
+		 * We always issue full-sector reads, but if some block in a
+		 * page fails to read, blk_update_request() will advance
+		 * bv_offset and adjust bv_len to compensate.  Print a warning
+		 * for unaligned offsets, and an error if they don't add up to
+		 * a full sector.
+		 */
+		if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
+			btrfs_err(fs_info,
+		"partial page read in btrfs with offset %u and length %u",
+				  bvec->bv_offset, bvec->bv_len);
+		else if (!IS_ALIGNED(bvec->bv_offset + bvec->bv_len,
+				     sectorsize))
+			btrfs_info(fs_info,
+		"incomplete page read with offset %u and length %u",
+				   bvec->bv_offset, bvec->bv_len);
+
+		start = page_offset(page) + bvec->bv_offset;
+		end = start + bvec->bv_len - 1;
+		len = bvec->bv_len;
+
+		if (likely(uptodate)) {
+			loff_t i_size = i_size_read(inode);
+			pgoff_t end_index = i_size >> PAGE_SHIFT;
+
+			/*
+			 * Zero out the remaining part if this range straddles
+			 * i_size.
+			 *
+			 * Here we should only zero the range inside the bvec,
+			 * not touch anything else.
+			 *
+			 * NOTE: i_size is exclusive while end is inclusive.
+			 */
+			if (page->index == end_index && i_size <= end) {
+				u32 zero_start = max(offset_in_page(i_size),
+						     offset_in_page(start));
+
+				zero_user_segment(page, zero_start,
+						  offset_in_page(end) + 1);
+			}
+		}
+
+		/* Update page status and unlock. */
+		end_page_read(page, uptodate, start, len);
+		endio_readpage_release_extent(&processed, BTRFS_I(inode),
+					      start, end, uptodate);
+
+		ASSERT(bio_offset + len > bio_offset);
+		bio_offset += len;
+
+	}
+	/* Release the last extent */
+	endio_readpage_release_extent(&processed, NULL, 0, 0, false);
+	bio_put(bio);
+}
+
+/*
+ * Populate every free slot in a provided array with pages.
+ *
+ * @nr_pages:   number of pages to allocate
+ * @page_array: the array to fill with pages; any existing non-null entries in
+ * 		the array will be skipped
+ *
+ * Return: 0        if all pages were able to be allocated;
+ *         -ENOMEM  otherwise, the partially allocated pages would be freed and
+ *                  the array slots zeroed
+ */
+int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array)
+{
+	unsigned int allocated;
+
+	for (allocated = 0; allocated < nr_pages;) {
+		unsigned int last = allocated;
+
+		allocated = alloc_pages_bulk_array(GFP_NOFS, nr_pages, page_array);
+
+		if (allocated == nr_pages)
+			return 0;
+
+		/*
+		 * During this iteration, no page could be allocated, even
+		 * though alloc_pages_bulk_array() falls back to alloc_page()
+		 * if  it could not bulk-allocate. So we must be out of memory.
+		 */
+		if (allocated == last) {
+			for (int i = 0; i < allocated; i++) {
+				__free_page(page_array[i]);
+				page_array[i] = NULL;
+			}
+			return -ENOMEM;
+		}
+
+		memalloc_retry_wait(GFP_NOFS);
+	}
+	return 0;
+}
+
+static bool btrfs_bio_is_contig(struct btrfs_bio_ctrl *bio_ctrl,
+				struct page *page, u64 disk_bytenr,
+				unsigned int pg_offset)
+{
+	struct bio *bio = &bio_ctrl->bbio->bio;
+	struct bio_vec *bvec = bio_last_bvec_all(bio);
+	const sector_t sector = disk_bytenr >> SECTOR_SHIFT;
+
+	if (bio_ctrl->compress_type != BTRFS_COMPRESS_NONE) {
+		/*
+		 * For compression, all IO should have its logical bytenr set
+		 * to the starting bytenr of the compressed extent.
+		 */
+		return bio->bi_iter.bi_sector == sector;
+	}
+
+	/*
+	 * The contig check requires the following conditions to be met:
+	 *
+	 * 1) The pages are belonging to the same inode
+	 *    This is implied by the call chain.
+	 *
+	 * 2) The range has adjacent logical bytenr
+	 *
+	 * 3) The range has adjacent file offset
+	 *    This is required for the usage of btrfs_bio->file_offset.
+	 */
+	return bio_end_sector(bio) == sector &&
+		page_offset(bvec->bv_page) + bvec->bv_offset + bvec->bv_len ==
+		page_offset(page) + pg_offset;
+}
+
+static void alloc_new_bio(struct btrfs_inode *inode,
+			  struct btrfs_bio_ctrl *bio_ctrl,
+			  u64 disk_bytenr, u64 file_offset)
+{
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+	struct btrfs_bio *bbio;
+
+	bbio = btrfs_bio_alloc(BIO_MAX_VECS, bio_ctrl->opf, fs_info,
+			       bio_ctrl->end_io_func, NULL);
+	bbio->bio.bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT;
+	bbio->inode = inode;
+	bbio->file_offset = file_offset;
+	bio_ctrl->bbio = bbio;
+	bio_ctrl->len_to_oe_boundary = U32_MAX;
+
+	/* Limit data write bios to the ordered boundary. */
+	if (bio_ctrl->wbc) {
+		struct btrfs_ordered_extent *ordered;
+
+		ordered = btrfs_lookup_ordered_extent(inode, file_offset);
+		if (ordered) {
+			bio_ctrl->len_to_oe_boundary = min_t(u32, U32_MAX,
+					ordered->file_offset +
+					ordered->disk_num_bytes - file_offset);
+			bbio->ordered = ordered;
+		}
+
+		/*
+		 * Pick the last added device to support cgroup writeback.  For
+		 * multi-device file systems this means blk-cgroup policies have
+		 * to always be set on the last added/replaced device.
+		 * This is a bit odd but has been like that for a long time.
+		 */
+		bio_set_dev(&bbio->bio, fs_info->fs_devices->latest_dev->bdev);
+		wbc_init_bio(bio_ctrl->wbc, &bbio->bio);
+	}
+}
+
+/*
+ * @disk_bytenr: logical bytenr where the write will be
+ * @page:	page to add to the bio
+ * @size:	portion of page that we want to write to
+ * @pg_offset:	offset of the new bio or to check whether we are adding
+ *              a contiguous page to the previous one
+ *
+ * The will either add the page into the existing @bio_ctrl->bbio, or allocate a
+ * new one in @bio_ctrl->bbio.
+ * The mirror number for this IO should already be initizlied in
+ * @bio_ctrl->mirror_num.
+ */
+static void submit_extent_page(struct btrfs_bio_ctrl *bio_ctrl,
+			       u64 disk_bytenr, struct page *page,
+			       size_t size, unsigned long pg_offset)
+{
+	struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
+
+	ASSERT(pg_offset + size <= PAGE_SIZE);
+	ASSERT(bio_ctrl->end_io_func);
+
+	if (bio_ctrl->bbio &&
+	    !btrfs_bio_is_contig(bio_ctrl, page, disk_bytenr, pg_offset))
+		submit_one_bio(bio_ctrl);
+
+	do {
+		u32 len = size;
+
+		/* Allocate new bio if needed */
+		if (!bio_ctrl->bbio) {
+			alloc_new_bio(inode, bio_ctrl, disk_bytenr,
+				      page_offset(page) + pg_offset);
+		}
+
+		/* Cap to the current ordered extent boundary if there is one. */
+		if (len > bio_ctrl->len_to_oe_boundary) {
+			ASSERT(bio_ctrl->compress_type == BTRFS_COMPRESS_NONE);
+			ASSERT(is_data_inode(&inode->vfs_inode));
+			len = bio_ctrl->len_to_oe_boundary;
+		}
+
+		if (bio_add_page(&bio_ctrl->bbio->bio, page, len, pg_offset) != len) {
+			/* bio full: move on to a new one */
+			submit_one_bio(bio_ctrl);
+			continue;
+		}
+
+		if (bio_ctrl->wbc)
+			wbc_account_cgroup_owner(bio_ctrl->wbc, page, len);
+
+		size -= len;
+		pg_offset += len;
+		disk_bytenr += len;
+
+		/*
+		 * len_to_oe_boundary defaults to U32_MAX, which isn't page or
+		 * sector aligned.  alloc_new_bio() then sets it to the end of
+		 * our ordered extent for writes into zoned devices.
+		 *
+		 * When len_to_oe_boundary is tracking an ordered extent, we
+		 * trust the ordered extent code to align things properly, and
+		 * the check above to cap our write to the ordered extent
+		 * boundary is correct.
+		 *
+		 * When len_to_oe_boundary is U32_MAX, the cap above would
+		 * result in a 4095 byte IO for the last page right before
+		 * we hit the bio limit of UINT_MAX.  bio_add_page() has all
+		 * the checks required to make sure we don't overflow the bio,
+		 * and we should just ignore len_to_oe_boundary completely
+		 * unless we're using it to track an ordered extent.
+		 *
+		 * It's pretty hard to make a bio sized U32_MAX, but it can
+		 * happen when the page cache is able to feed us contiguous
+		 * pages for large extents.
+		 */
+		if (bio_ctrl->len_to_oe_boundary != U32_MAX)
+			bio_ctrl->len_to_oe_boundary -= len;
+
+		/* Ordered extent boundary: move on to a new bio. */
+		if (bio_ctrl->len_to_oe_boundary == 0)
+			submit_one_bio(bio_ctrl);
+	} while (size);
+}
+
+static int attach_extent_buffer_page(struct extent_buffer *eb,
+				     struct page *page,
+				     struct btrfs_subpage *prealloc)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	int ret = 0;
+
+	/*
+	 * If the page is mapped to btree inode, we should hold the private
+	 * lock to prevent race.
+	 * For cloned or dummy extent buffers, their pages are not mapped and
+	 * will not race with any other ebs.
+	 */
+	if (page->mapping)
+		lockdep_assert_held(&page->mapping->private_lock);
+
+	if (fs_info->nodesize >= PAGE_SIZE) {
+		if (!PagePrivate(page))
+			attach_page_private(page, eb);
+		else
+			WARN_ON(page->private != (unsigned long)eb);
+		return 0;
+	}
+
+	/* Already mapped, just free prealloc */
+	if (PagePrivate(page)) {
+		btrfs_free_subpage(prealloc);
+		return 0;
+	}
+
+	if (prealloc)
+		/* Has preallocated memory for subpage */
+		attach_page_private(page, prealloc);
+	else
+		/* Do new allocation to attach subpage */
+		ret = btrfs_attach_subpage(fs_info, page,
+					   BTRFS_SUBPAGE_METADATA);
+	return ret;
+}
+
+int set_page_extent_mapped(struct page *page)
+{
+	struct btrfs_fs_info *fs_info;
+
+	ASSERT(page->mapping);
+
+	if (PagePrivate(page))
+		return 0;
+
+	fs_info = btrfs_sb(page->mapping->host->i_sb);
+
+	if (btrfs_is_subpage(fs_info, page))
+		return btrfs_attach_subpage(fs_info, page, BTRFS_SUBPAGE_DATA);
+
+	attach_page_private(page, (void *)EXTENT_PAGE_PRIVATE);
+	return 0;
+}
+
+void clear_page_extent_mapped(struct page *page)
+{
+	struct btrfs_fs_info *fs_info;
+
+	ASSERT(page->mapping);
+
+	if (!PagePrivate(page))
+		return;
+
+	fs_info = btrfs_sb(page->mapping->host->i_sb);
+	if (btrfs_is_subpage(fs_info, page))
+		return btrfs_detach_subpage(fs_info, page);
+
+	detach_page_private(page);
+}
+
+static struct extent_map *
+__get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
+		 u64 start, u64 len, struct extent_map **em_cached)
+{
+	struct extent_map *em;
+
+	if (em_cached && *em_cached) {
+		em = *em_cached;
+		if (extent_map_in_tree(em) && start >= em->start &&
+		    start < extent_map_end(em)) {
+			refcount_inc(&em->refs);
+			return em;
+		}
+
+		free_extent_map(em);
+		*em_cached = NULL;
+	}
+
+	em = btrfs_get_extent(BTRFS_I(inode), page, pg_offset, start, len);
+	if (em_cached && !IS_ERR(em)) {
+		BUG_ON(*em_cached);
+		refcount_inc(&em->refs);
+		*em_cached = em;
+	}
+	return em;
+}
+/*
+ * basic readpage implementation.  Locked extent state structs are inserted
+ * into the tree that are removed when the IO is done (by the end_io
+ * handlers)
+ * XXX JDM: This needs looking at to ensure proper page locking
+ * return 0 on success, otherwise return error
+ */
+static int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
+		      struct btrfs_bio_ctrl *bio_ctrl, u64 *prev_em_start)
+{
+	struct inode *inode = page->mapping->host;
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	u64 start = page_offset(page);
+	const u64 end = start + PAGE_SIZE - 1;
+	u64 cur = start;
+	u64 extent_offset;
+	u64 last_byte = i_size_read(inode);
+	u64 block_start;
+	struct extent_map *em;
+	int ret = 0;
+	size_t pg_offset = 0;
+	size_t iosize;
+	size_t blocksize = inode->i_sb->s_blocksize;
+	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
+
+	ret = set_page_extent_mapped(page);
+	if (ret < 0) {
+		unlock_extent(tree, start, end, NULL);
+		unlock_page(page);
+		return ret;
+	}
+
+	if (page->index == last_byte >> PAGE_SHIFT) {
+		size_t zero_offset = offset_in_page(last_byte);
+
+		if (zero_offset) {
+			iosize = PAGE_SIZE - zero_offset;
+			memzero_page(page, zero_offset, iosize);
+		}
+	}
+	bio_ctrl->end_io_func = end_bio_extent_readpage;
+	begin_page_read(fs_info, page);
+	while (cur <= end) {
+		enum btrfs_compression_type compress_type = BTRFS_COMPRESS_NONE;
+		bool force_bio_submit = false;
+		u64 disk_bytenr;
+
+		ASSERT(IS_ALIGNED(cur, fs_info->sectorsize));
+		if (cur >= last_byte) {
+			iosize = PAGE_SIZE - pg_offset;
+			memzero_page(page, pg_offset, iosize);
+			unlock_extent(tree, cur, cur + iosize - 1, NULL);
+			end_page_read(page, true, cur, iosize);
+			break;
+		}
+		em = __get_extent_map(inode, page, pg_offset, cur,
+				      end - cur + 1, em_cached);
+		if (IS_ERR(em)) {
+			unlock_extent(tree, cur, end, NULL);
+			end_page_read(page, false, cur, end + 1 - cur);
+			return PTR_ERR(em);
+		}
+		extent_offset = cur - em->start;
+		BUG_ON(extent_map_end(em) <= cur);
+		BUG_ON(end < cur);
+
+		if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
+			compress_type = em->compress_type;
+
+		iosize = min(extent_map_end(em) - cur, end - cur + 1);
+		iosize = ALIGN(iosize, blocksize);
+		if (compress_type != BTRFS_COMPRESS_NONE)
+			disk_bytenr = em->block_start;
+		else
+			disk_bytenr = em->block_start + extent_offset;
+		block_start = em->block_start;
+		if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
+			block_start = EXTENT_MAP_HOLE;
+
+		/*
+		 * If we have a file range that points to a compressed extent
+		 * and it's followed by a consecutive file range that points
+		 * to the same compressed extent (possibly with a different
+		 * offset and/or length, so it either points to the whole extent
+		 * or only part of it), we must make sure we do not submit a
+		 * single bio to populate the pages for the 2 ranges because
+		 * this makes the compressed extent read zero out the pages
+		 * belonging to the 2nd range. Imagine the following scenario:
+		 *
+		 *  File layout
+		 *  [0 - 8K]                     [8K - 24K]
+		 *    |                               |
+		 *    |                               |
+		 * points to extent X,         points to extent X,
+		 * offset 4K, length of 8K     offset 0, length 16K
+		 *
+		 * [extent X, compressed length = 4K uncompressed length = 16K]
+		 *
+		 * If the bio to read the compressed extent covers both ranges,
+		 * it will decompress extent X into the pages belonging to the
+		 * first range and then it will stop, zeroing out the remaining
+		 * pages that belong to the other range that points to extent X.
+		 * So here we make sure we submit 2 bios, one for the first
+		 * range and another one for the third range. Both will target
+		 * the same physical extent from disk, but we can't currently
+		 * make the compressed bio endio callback populate the pages
+		 * for both ranges because each compressed bio is tightly
+		 * coupled with a single extent map, and each range can have
+		 * an extent map with a different offset value relative to the
+		 * uncompressed data of our extent and different lengths. This
+		 * is a corner case so we prioritize correctness over
+		 * non-optimal behavior (submitting 2 bios for the same extent).
+		 */
+		if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags) &&
+		    prev_em_start && *prev_em_start != (u64)-1 &&
+		    *prev_em_start != em->start)
+			force_bio_submit = true;
+
+		if (prev_em_start)
+			*prev_em_start = em->start;
+
+		free_extent_map(em);
+		em = NULL;
+
+		/* we've found a hole, just zero and go on */
+		if (block_start == EXTENT_MAP_HOLE) {
+			memzero_page(page, pg_offset, iosize);
+
+			unlock_extent(tree, cur, cur + iosize - 1, NULL);
+			end_page_read(page, true, cur, iosize);
+			cur = cur + iosize;
+			pg_offset += iosize;
+			continue;
+		}
+		/* the get_extent function already copied into the page */
+		if (block_start == EXTENT_MAP_INLINE) {
+			unlock_extent(tree, cur, cur + iosize - 1, NULL);
+			end_page_read(page, true, cur, iosize);
+			cur = cur + iosize;
+			pg_offset += iosize;
+			continue;
+		}
+
+		if (bio_ctrl->compress_type != compress_type) {
+			submit_one_bio(bio_ctrl);
+			bio_ctrl->compress_type = compress_type;
+		}
+
+		if (force_bio_submit)
+			submit_one_bio(bio_ctrl);
+		submit_extent_page(bio_ctrl, disk_bytenr, page, iosize,
+				   pg_offset);
+		cur = cur + iosize;
+		pg_offset += iosize;
+	}
+
+	return 0;
+}
+
+int btrfs_read_folio(struct file *file, struct folio *folio)
+{
+	struct page *page = &folio->page;
+	struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
+	u64 start = page_offset(page);
+	u64 end = start + PAGE_SIZE - 1;
+	struct btrfs_bio_ctrl bio_ctrl = { .opf = REQ_OP_READ };
+	int ret;
+
+	btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);
+
+	ret = btrfs_do_readpage(page, NULL, &bio_ctrl, NULL);
+	/*
+	 * If btrfs_do_readpage() failed we will want to submit the assembled
+	 * bio to do the cleanup.
+	 */
+	submit_one_bio(&bio_ctrl);
+	return ret;
+}
+
+static inline void contiguous_readpages(struct page *pages[], int nr_pages,
+					u64 start, u64 end,
+					struct extent_map **em_cached,
+					struct btrfs_bio_ctrl *bio_ctrl,
+					u64 *prev_em_start)
+{
+	struct btrfs_inode *inode = BTRFS_I(pages[0]->mapping->host);
+	int index;
+
+	btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);
+
+	for (index = 0; index < nr_pages; index++) {
+		btrfs_do_readpage(pages[index], em_cached, bio_ctrl,
+				  prev_em_start);
+		put_page(pages[index]);
+	}
+}
+
+/*
+ * helper for __extent_writepage, doing all of the delayed allocation setup.
+ *
+ * This returns 1 if btrfs_run_delalloc_range function did all the work required
+ * to write the page (copy into inline extent).  In this case the IO has
+ * been started and the page is already unlocked.
+ *
+ * This returns 0 if all went well (page still locked)
+ * This returns < 0 if there were errors (page still locked)
+ */
+static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
+		struct page *page, struct writeback_control *wbc)
+{
+	const u64 page_start = page_offset(page);
+	const u64 page_end = page_start + PAGE_SIZE - 1;
+	u64 delalloc_start = page_start;
+	u64 delalloc_end = page_end;
+	u64 delalloc_to_write = 0;
+	int ret = 0;
+
+	while (delalloc_start < page_end) {
+		delalloc_end = page_end;
+		if (!find_lock_delalloc_range(&inode->vfs_inode, page,
+					      &delalloc_start, &delalloc_end)) {
+			delalloc_start = delalloc_end + 1;
+			continue;
+		}
+
+		ret = btrfs_run_delalloc_range(inode, page, delalloc_start,
+					       delalloc_end, wbc);
+		if (ret < 0)
+			return ret;
+
+		delalloc_start = delalloc_end + 1;
+	}
+
+	/*
+	 * delalloc_end is already one less than the total length, so
+	 * we don't subtract one from PAGE_SIZE
+	 */
+	delalloc_to_write +=
+		DIV_ROUND_UP(delalloc_end + 1 - page_start, PAGE_SIZE);
+
+	/*
+	 * If btrfs_run_dealloc_range() already started I/O and unlocked
+	 * the pages, we just need to account for them here.
+	 */
+	if (ret == 1) {
+		wbc->nr_to_write -= delalloc_to_write;
+		return 1;
+	}
+
+	if (wbc->nr_to_write < delalloc_to_write) {
+		int thresh = 8192;
+
+		if (delalloc_to_write < thresh * 2)
+			thresh = delalloc_to_write;
+		wbc->nr_to_write = min_t(u64, delalloc_to_write,
+					 thresh);
+	}
+
+	return 0;
+}
+
+/*
+ * Find the first byte we need to write.
+ *
+ * For subpage, one page can contain several sectors, and
+ * __extent_writepage_io() will just grab all extent maps in the page
+ * range and try to submit all non-inline/non-compressed extents.
+ *
+ * This is a big problem for subpage, we shouldn't re-submit already written
+ * data at all.
+ * This function will lookup subpage dirty bit to find which range we really
+ * need to submit.
+ *
+ * Return the next dirty range in [@start, @end).
+ * If no dirty range is found, @start will be page_offset(page) + PAGE_SIZE.
+ */
+static void find_next_dirty_byte(struct btrfs_fs_info *fs_info,
+				 struct page *page, u64 *start, u64 *end)
+{
+	struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
+	struct btrfs_subpage_info *spi = fs_info->subpage_info;
+	u64 orig_start = *start;
+	/* Declare as unsigned long so we can use bitmap ops */
+	unsigned long flags;
+	int range_start_bit;
+	int range_end_bit;
+
+	/*
+	 * For regular sector size == page size case, since one page only
+	 * contains one sector, we return the page offset directly.
+	 */
+	if (!btrfs_is_subpage(fs_info, page)) {
+		*start = page_offset(page);
+		*end = page_offset(page) + PAGE_SIZE;
+		return;
+	}
+
+	range_start_bit = spi->dirty_offset +
+			  (offset_in_page(orig_start) >> fs_info->sectorsize_bits);
+
+	/* We should have the page locked, but just in case */
+	spin_lock_irqsave(&subpage->lock, flags);
+	bitmap_next_set_region(subpage->bitmaps, &range_start_bit, &range_end_bit,
+			       spi->dirty_offset + spi->bitmap_nr_bits);
+	spin_unlock_irqrestore(&subpage->lock, flags);
+
+	range_start_bit -= spi->dirty_offset;
+	range_end_bit -= spi->dirty_offset;
+
+	*start = page_offset(page) + range_start_bit * fs_info->sectorsize;
+	*end = page_offset(page) + range_end_bit * fs_info->sectorsize;
+}
+
+/*
+ * helper for __extent_writepage.  This calls the writepage start hooks,
+ * and does the loop to map the page into extents and bios.
+ *
+ * We return 1 if the IO is started and the page is unlocked,
+ * 0 if all went well (page still locked)
+ * < 0 if there were errors (page still locked)
+ */
+static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
+				 struct page *page,
+				 struct btrfs_bio_ctrl *bio_ctrl,
+				 loff_t i_size,
+				 int *nr_ret)
+{
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+	u64 cur = page_offset(page);
+	u64 end = cur + PAGE_SIZE - 1;
+	u64 extent_offset;
+	u64 block_start;
+	struct extent_map *em;
+	int ret = 0;
+	int nr = 0;
+
+	ret = btrfs_writepage_cow_fixup(page);
+	if (ret) {
+		/* Fixup worker will requeue */
+		redirty_page_for_writepage(bio_ctrl->wbc, page);
+		unlock_page(page);
+		return 1;
+	}
+
+	bio_ctrl->end_io_func = end_bio_extent_writepage;
+	while (cur <= end) {
+		u32 len = end - cur + 1;
+		u64 disk_bytenr;
+		u64 em_end;
+		u64 dirty_range_start = cur;
+		u64 dirty_range_end;
+		u32 iosize;
+
+		if (cur >= i_size) {
+			btrfs_mark_ordered_io_finished(inode, page, cur, len,
+						       true);
+			/*
+			 * This range is beyond i_size, thus we don't need to
+			 * bother writing back.
+			 * But we still need to clear the dirty subpage bit, or
+			 * the next time the page gets dirtied, we will try to
+			 * writeback the sectors with subpage dirty bits,
+			 * causing writeback without ordered extent.
+			 */
+			btrfs_page_clear_dirty(fs_info, page, cur, len);
+			break;
+		}
+
+		find_next_dirty_byte(fs_info, page, &dirty_range_start,
+				     &dirty_range_end);
+		if (cur < dirty_range_start) {
+			cur = dirty_range_start;
+			continue;
+		}
+
+		em = btrfs_get_extent(inode, NULL, 0, cur, len);
+		if (IS_ERR(em)) {
+			ret = PTR_ERR_OR_ZERO(em);
+			goto out_error;
+		}
+
+		extent_offset = cur - em->start;
+		em_end = extent_map_end(em);
+		ASSERT(cur <= em_end);
+		ASSERT(cur < end);
+		ASSERT(IS_ALIGNED(em->start, fs_info->sectorsize));
+		ASSERT(IS_ALIGNED(em->len, fs_info->sectorsize));
+
+		block_start = em->block_start;
+		disk_bytenr = em->block_start + extent_offset;
+
+		ASSERT(!test_bit(EXTENT_FLAG_COMPRESSED, &em->flags));
+		ASSERT(block_start != EXTENT_MAP_HOLE);
+		ASSERT(block_start != EXTENT_MAP_INLINE);
+
+		/*
+		 * Note that em_end from extent_map_end() and dirty_range_end from
+		 * find_next_dirty_byte() are all exclusive
+		 */
+		iosize = min(min(em_end, end + 1), dirty_range_end) - cur;
+		free_extent_map(em);
+		em = NULL;
+
+		btrfs_set_range_writeback(inode, cur, cur + iosize - 1);
+		if (!PageWriteback(page)) {
+			btrfs_err(inode->root->fs_info,
+				   "page %lu not writeback, cur %llu end %llu",
+			       page->index, cur, end);
+		}
+
+		/*
+		 * Although the PageDirty bit is cleared before entering this
+		 * function, subpage dirty bit is not cleared.
+		 * So clear subpage dirty bit here so next time we won't submit
+		 * page for range already written to disk.
+		 */
+		btrfs_page_clear_dirty(fs_info, page, cur, iosize);
+
+		submit_extent_page(bio_ctrl, disk_bytenr, page, iosize,
+				   cur - page_offset(page));
+		cur += iosize;
+		nr++;
+	}
+
+	btrfs_page_assert_not_dirty(fs_info, page);
+	*nr_ret = nr;
+	return 0;
+
+out_error:
+	/*
+	 * If we finish without problem, we should not only clear page dirty,
+	 * but also empty subpage dirty bits
+	 */
+	*nr_ret = nr;
+	return ret;
+}
+
+/*
+ * the writepage semantics are similar to regular writepage.  extent
+ * records are inserted to lock ranges in the tree, and as dirty areas
+ * are found, they are marked writeback.  Then the lock bits are removed
+ * and the end_io handler clears the writeback ranges
+ *
+ * Return 0 if everything goes well.
+ * Return <0 for error.
+ */
+static int __extent_writepage(struct page *page, struct btrfs_bio_ctrl *bio_ctrl)
+{
+	struct folio *folio = page_folio(page);
+	struct inode *inode = page->mapping->host;
+	const u64 page_start = page_offset(page);
+	int ret;
+	int nr = 0;
+	size_t pg_offset;
+	loff_t i_size = i_size_read(inode);
+	unsigned long end_index = i_size >> PAGE_SHIFT;
+
+	trace___extent_writepage(page, inode, bio_ctrl->wbc);
+
+	WARN_ON(!PageLocked(page));
+
+	pg_offset = offset_in_page(i_size);
+	if (page->index > end_index ||
+	   (page->index == end_index && !pg_offset)) {
+		folio_invalidate(folio, 0, folio_size(folio));
+		folio_unlock(folio);
+		return 0;
+	}
+
+	if (page->index == end_index)
+		memzero_page(page, pg_offset, PAGE_SIZE - pg_offset);
+
+	ret = set_page_extent_mapped(page);
+	if (ret < 0)
+		goto done;
+
+	ret = writepage_delalloc(BTRFS_I(inode), page, bio_ctrl->wbc);
+	if (ret == 1)
+		return 0;
+	if (ret)
+		goto done;
+
+	ret = __extent_writepage_io(BTRFS_I(inode), page, bio_ctrl, i_size, &nr);
+	if (ret == 1)
+		return 0;
+
+	bio_ctrl->wbc->nr_to_write--;
+
+done:
+	if (nr == 0) {
+		/* make sure the mapping tag for page dirty gets cleared */
+		set_page_writeback(page);
+		end_page_writeback(page);
+	}
+	if (ret) {
+		btrfs_mark_ordered_io_finished(BTRFS_I(inode), page, page_start,
+					       PAGE_SIZE, !ret);
+		mapping_set_error(page->mapping, ret);
+	}
+	unlock_page(page);
+	ASSERT(ret <= 0);
+	return ret;
+}
+
+void wait_on_extent_buffer_writeback(struct extent_buffer *eb)
+{
+	wait_on_bit_io(&eb->bflags, EXTENT_BUFFER_WRITEBACK,
+		       TASK_UNINTERRUPTIBLE);
+}
+
+/*
+ * Lock extent buffer status and pages for writeback.
+ *
+ * Return %false if the extent buffer doesn't need to be submitted (e.g. the
+ * extent buffer is not dirty)
+ * Return %true is the extent buffer is submitted to bio.
+ */
+static noinline_for_stack bool lock_extent_buffer_for_io(struct extent_buffer *eb,
+			  struct writeback_control *wbc)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	bool ret = false;
+
+	btrfs_tree_lock(eb);
+	while (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
+		btrfs_tree_unlock(eb);
+		if (wbc->sync_mode != WB_SYNC_ALL)
+			return false;
+		wait_on_extent_buffer_writeback(eb);
+		btrfs_tree_lock(eb);
+	}
+
+	/*
+	 * We need to do this to prevent races in people who check if the eb is
+	 * under IO since we can end up having no IO bits set for a short period
+	 * of time.
+	 */
+	spin_lock(&eb->refs_lock);
+	if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
+		set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
+		spin_unlock(&eb->refs_lock);
+		btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
+		percpu_counter_add_batch(&fs_info->dirty_metadata_bytes,
+					 -eb->len,
+					 fs_info->dirty_metadata_batch);
+		ret = true;
+	} else {
+		spin_unlock(&eb->refs_lock);
+	}
+	btrfs_tree_unlock(eb);
+	return ret;
+}
+
+static void set_btree_ioerr(struct extent_buffer *eb)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+
+	set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
+
+	/*
+	 * A read may stumble upon this buffer later, make sure that it gets an
+	 * error and knows there was an error.
+	 */
+	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
+
+	/*
+	 * We need to set the mapping with the io error as well because a write
+	 * error will flip the file system readonly, and then syncfs() will
+	 * return a 0 because we are readonly if we don't modify the err seq for
+	 * the superblock.
+	 */
+	mapping_set_error(eb->fs_info->btree_inode->i_mapping, -EIO);
+
+	/*
+	 * If writeback for a btree extent that doesn't belong to a log tree
+	 * failed, increment the counter transaction->eb_write_errors.
+	 * We do this because while the transaction is running and before it's
+	 * committing (when we call filemap_fdata[write|wait]_range against
+	 * the btree inode), we might have
+	 * btree_inode->i_mapping->a_ops->writepages() called by the VM - if it
+	 * returns an error or an error happens during writeback, when we're
+	 * committing the transaction we wouldn't know about it, since the pages
+	 * can be no longer dirty nor marked anymore for writeback (if a
+	 * subsequent modification to the extent buffer didn't happen before the
+	 * transaction commit), which makes filemap_fdata[write|wait]_range not
+	 * able to find the pages tagged with SetPageError at transaction
+	 * commit time. So if this happens we must abort the transaction,
+	 * otherwise we commit a super block with btree roots that point to
+	 * btree nodes/leafs whose content on disk is invalid - either garbage
+	 * or the content of some node/leaf from a past generation that got
+	 * cowed or deleted and is no longer valid.
+	 *
+	 * Note: setting AS_EIO/AS_ENOSPC in the btree inode's i_mapping would
+	 * not be enough - we need to distinguish between log tree extents vs
+	 * non-log tree extents, and the next filemap_fdatawait_range() call
+	 * will catch and clear such errors in the mapping - and that call might
+	 * be from a log sync and not from a transaction commit. Also, checking
+	 * for the eb flag EXTENT_BUFFER_WRITE_ERR at transaction commit time is
+	 * not done and would not be reliable - the eb might have been released
+	 * from memory and reading it back again means that flag would not be
+	 * set (since it's a runtime flag, not persisted on disk).
+	 *
+	 * Using the flags below in the btree inode also makes us achieve the
+	 * goal of AS_EIO/AS_ENOSPC when writepages() returns success, started
+	 * writeback for all dirty pages and before filemap_fdatawait_range()
+	 * is called, the writeback for all dirty pages had already finished
+	 * with errors - because we were not using AS_EIO/AS_ENOSPC,
+	 * filemap_fdatawait_range() would return success, as it could not know
+	 * that writeback errors happened (the pages were no longer tagged for
+	 * writeback).
+	 */
+	switch (eb->log_index) {
+	case -1:
+		set_bit(BTRFS_FS_BTREE_ERR, &fs_info->flags);
+		break;
+	case 0:
+		set_bit(BTRFS_FS_LOG1_ERR, &fs_info->flags);
+		break;
+	case 1:
+		set_bit(BTRFS_FS_LOG2_ERR, &fs_info->flags);
+		break;
+	default:
+		BUG(); /* unexpected, logic error */
+	}
+}
+
+/*
+ * The endio specific version which won't touch any unsafe spinlock in endio
+ * context.
+ */
+static struct extent_buffer *find_extent_buffer_nolock(
+		struct btrfs_fs_info *fs_info, u64 start)
+{
+	struct extent_buffer *eb;
+
+	rcu_read_lock();
+	eb = radix_tree_lookup(&fs_info->buffer_radix,
+			       start >> fs_info->sectorsize_bits);
+	if (eb && atomic_inc_not_zero(&eb->refs)) {
+		rcu_read_unlock();
+		return eb;
+	}
+	rcu_read_unlock();
+	return NULL;
+}
+
+static void extent_buffer_write_end_io(struct btrfs_bio *bbio)
+{
+	struct extent_buffer *eb = bbio->private;
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	bool uptodate = !bbio->bio.bi_status;
+	struct bvec_iter_all iter_all;
+	struct bio_vec *bvec;
+	u32 bio_offset = 0;
+
+	if (!uptodate)
+		set_btree_ioerr(eb);
+
+	bio_for_each_segment_all(bvec, &bbio->bio, iter_all) {
+		u64 start = eb->start + bio_offset;
+		struct page *page = bvec->bv_page;
+		u32 len = bvec->bv_len;
+
+		btrfs_page_clear_writeback(fs_info, page, start, len);
+		bio_offset += len;
+	}
+
+	clear_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
+	smp_mb__after_atomic();
+	wake_up_bit(&eb->bflags, EXTENT_BUFFER_WRITEBACK);
+
+	bio_put(&bbio->bio);
+}
+
+static void prepare_eb_write(struct extent_buffer *eb)
+{
+	u32 nritems;
+	unsigned long start;
+	unsigned long end;
+
+	clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
+
+	/* Set btree blocks beyond nritems with 0 to avoid stale content */
+	nritems = btrfs_header_nritems(eb);
+	if (btrfs_header_level(eb) > 0) {
+		end = btrfs_node_key_ptr_offset(eb, nritems);
+		memzero_extent_buffer(eb, end, eb->len - end);
+	} else {
+		/*
+		 * Leaf:
+		 * header 0 1 2 .. N ... data_N .. data_2 data_1 data_0
+		 */
+		start = btrfs_item_nr_offset(eb, nritems);
+		end = btrfs_item_nr_offset(eb, 0);
+		if (nritems == 0)
+			end += BTRFS_LEAF_DATA_SIZE(eb->fs_info);
+		else
+			end += btrfs_item_offset(eb, nritems - 1);
+		memzero_extent_buffer(eb, start, end - start);
+	}
+}
+
+static noinline_for_stack void write_one_eb(struct extent_buffer *eb,
+					    struct writeback_control *wbc)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	struct btrfs_bio *bbio;
+
+	prepare_eb_write(eb);
+
+	bbio = btrfs_bio_alloc(INLINE_EXTENT_BUFFER_PAGES,
+			       REQ_OP_WRITE | REQ_META | wbc_to_write_flags(wbc),
+			       eb->fs_info, extent_buffer_write_end_io, eb);
+	bbio->bio.bi_iter.bi_sector = eb->start >> SECTOR_SHIFT;
+	bio_set_dev(&bbio->bio, fs_info->fs_devices->latest_dev->bdev);
+	wbc_init_bio(wbc, &bbio->bio);
+	bbio->inode = BTRFS_I(eb->fs_info->btree_inode);
+	bbio->file_offset = eb->start;
+	if (fs_info->nodesize < PAGE_SIZE) {
+		struct page *p = eb->pages[0];
+
+		lock_page(p);
+		btrfs_subpage_set_writeback(fs_info, p, eb->start, eb->len);
+		if (btrfs_subpage_clear_and_test_dirty(fs_info, p, eb->start,
+						       eb->len)) {
+			clear_page_dirty_for_io(p);
+			wbc->nr_to_write--;
+		}
+		__bio_add_page(&bbio->bio, p, eb->len, eb->start - page_offset(p));
+		wbc_account_cgroup_owner(wbc, p, eb->len);
+		unlock_page(p);
+	} else {
+		for (int i = 0; i < num_extent_pages(eb); i++) {
+			struct page *p = eb->pages[i];
+
+			lock_page(p);
+			clear_page_dirty_for_io(p);
+			set_page_writeback(p);
+			__bio_add_page(&bbio->bio, p, PAGE_SIZE, 0);
+			wbc_account_cgroup_owner(wbc, p, PAGE_SIZE);
+			wbc->nr_to_write--;
+			unlock_page(p);
+		}
+	}
+	btrfs_submit_bio(bbio, 0);
+}
+
+/*
+ * Submit one subpage btree page.
+ *
+ * The main difference to submit_eb_page() is:
+ * - Page locking
+ *   For subpage, we don't rely on page locking at all.
+ *
+ * - Flush write bio
+ *   We only flush bio if we may be unable to fit current extent buffers into
+ *   current bio.
+ *
+ * Return >=0 for the number of submitted extent buffers.
+ * Return <0 for fatal error.
+ */
+static int submit_eb_subpage(struct page *page, struct writeback_control *wbc)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+	int submitted = 0;
+	u64 page_start = page_offset(page);
+	int bit_start = 0;
+	int sectors_per_node = fs_info->nodesize >> fs_info->sectorsize_bits;
+
+	/* Lock and write each dirty extent buffers in the range */
+	while (bit_start < fs_info->subpage_info->bitmap_nr_bits) {
+		struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
+		struct extent_buffer *eb;
+		unsigned long flags;
+		u64 start;
+
+		/*
+		 * Take private lock to ensure the subpage won't be detached
+		 * in the meantime.
+		 */
+		spin_lock(&page->mapping->private_lock);
+		if (!PagePrivate(page)) {
+			spin_unlock(&page->mapping->private_lock);
+			break;
+		}
+		spin_lock_irqsave(&subpage->lock, flags);
+		if (!test_bit(bit_start + fs_info->subpage_info->dirty_offset,
+			      subpage->bitmaps)) {
+			spin_unlock_irqrestore(&subpage->lock, flags);
+			spin_unlock(&page->mapping->private_lock);
+			bit_start++;
+			continue;
+		}
+
+		start = page_start + bit_start * fs_info->sectorsize;
+		bit_start += sectors_per_node;
+
+		/*
+		 * Here we just want to grab the eb without touching extra
+		 * spin locks, so call find_extent_buffer_nolock().
+		 */
+		eb = find_extent_buffer_nolock(fs_info, start);
+		spin_unlock_irqrestore(&subpage->lock, flags);
+		spin_unlock(&page->mapping->private_lock);
+
+		/*
+		 * The eb has already reached 0 refs thus find_extent_buffer()
+		 * doesn't return it. We don't need to write back such eb
+		 * anyway.
+		 */
+		if (!eb)
+			continue;
+
+		if (lock_extent_buffer_for_io(eb, wbc)) {
+			write_one_eb(eb, wbc);
+			submitted++;
+		}
+		free_extent_buffer(eb);
+	}
+	return submitted;
+}
+
+/*
+ * Submit all page(s) of one extent buffer.
+ *
+ * @page:	the page of one extent buffer
+ * @eb_context:	to determine if we need to submit this page, if current page
+ *		belongs to this eb, we don't need to submit
+ *
+ * The caller should pass each page in their bytenr order, and here we use
+ * @eb_context to determine if we have submitted pages of one extent buffer.
+ *
+ * If we have, we just skip until we hit a new page that doesn't belong to
+ * current @eb_context.
+ *
+ * If not, we submit all the page(s) of the extent buffer.
+ *
+ * Return >0 if we have submitted the extent buffer successfully.
+ * Return 0 if we don't need to submit the page, as it's already submitted by
+ * previous call.
+ * Return <0 for fatal error.
+ */
+static int submit_eb_page(struct page *page, struct btrfs_eb_write_context *ctx)
+{
+	struct writeback_control *wbc = ctx->wbc;
+	struct address_space *mapping = page->mapping;
+	struct extent_buffer *eb;
+	int ret;
+
+	if (!PagePrivate(page))
+		return 0;
+
+	if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
+		return submit_eb_subpage(page, wbc);
+
+	spin_lock(&mapping->private_lock);
+	if (!PagePrivate(page)) {
+		spin_unlock(&mapping->private_lock);
+		return 0;
+	}
+
+	eb = (struct extent_buffer *)page->private;
+
+	/*
+	 * Shouldn't happen and normally this would be a BUG_ON but no point
+	 * crashing the machine for something we can survive anyway.
+	 */
+	if (WARN_ON(!eb)) {
+		spin_unlock(&mapping->private_lock);
+		return 0;
+	}
+
+	if (eb == ctx->eb) {
+		spin_unlock(&mapping->private_lock);
+		return 0;
+	}
+	ret = atomic_inc_not_zero(&eb->refs);
+	spin_unlock(&mapping->private_lock);
+	if (!ret)
+		return 0;
+
+	ctx->eb = eb;
+
+	ret = btrfs_check_meta_write_pointer(eb->fs_info, ctx);
+	if (ret) {
+		if (ret == -EBUSY)
+			ret = 0;
+		free_extent_buffer(eb);
+		return ret;
+	}
+
+	if (!lock_extent_buffer_for_io(eb, wbc)) {
+		free_extent_buffer(eb);
+		return 0;
+	}
+	/* Implies write in zoned mode. */
+	if (ctx->zoned_bg) {
+		/* Mark the last eb in the block group. */
+		btrfs_schedule_zone_finish_bg(ctx->zoned_bg, eb);
+		ctx->zoned_bg->meta_write_pointer += eb->len;
+	}
+	write_one_eb(eb, wbc);
+	free_extent_buffer(eb);
+	return 1;
+}
+
+int btree_write_cache_pages(struct address_space *mapping,
+				   struct writeback_control *wbc)
+{
+	struct btrfs_eb_write_context ctx = { .wbc = wbc };
+	struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
+	int ret = 0;
+	int done = 0;
+	int nr_to_write_done = 0;
+	struct folio_batch fbatch;
+	unsigned int nr_folios;
+	pgoff_t index;
+	pgoff_t end;		/* Inclusive */
+	int scanned = 0;
+	xa_mark_t tag;
+
+	folio_batch_init(&fbatch);
+	if (wbc->range_cyclic) {
+		index = mapping->writeback_index; /* Start from prev offset */
+		end = -1;
+		/*
+		 * Start from the beginning does not need to cycle over the
+		 * range, mark it as scanned.
+		 */
+		scanned = (index == 0);
+	} else {
+		index = wbc->range_start >> PAGE_SHIFT;
+		end = wbc->range_end >> PAGE_SHIFT;
+		scanned = 1;
+	}
+	if (wbc->sync_mode == WB_SYNC_ALL)
+		tag = PAGECACHE_TAG_TOWRITE;
+	else
+		tag = PAGECACHE_TAG_DIRTY;
+	btrfs_zoned_meta_io_lock(fs_info);
+retry:
+	if (wbc->sync_mode == WB_SYNC_ALL)
+		tag_pages_for_writeback(mapping, index, end);
+	while (!done && !nr_to_write_done && (index <= end) &&
+	       (nr_folios = filemap_get_folios_tag(mapping, &index, end,
+					    tag, &fbatch))) {
+		unsigned i;
+
+		for (i = 0; i < nr_folios; i++) {
+			struct folio *folio = fbatch.folios[i];
+
+			ret = submit_eb_page(&folio->page, &ctx);
+			if (ret == 0)
+				continue;
+			if (ret < 0) {
+				done = 1;
+				break;
+			}
+
+			/*
+			 * the filesystem may choose to bump up nr_to_write.
+			 * We have to make sure to honor the new nr_to_write
+			 * at any time
+			 */
+			nr_to_write_done = wbc->nr_to_write <= 0;
+		}
+		folio_batch_release(&fbatch);
+		cond_resched();
+	}
+	if (!scanned && !done) {
+		/*
+		 * We hit the last page and there is more work to be done: wrap
+		 * back to the start of the file
+		 */
+		scanned = 1;
+		index = 0;
+		goto retry;
+	}
+	/*
+	 * If something went wrong, don't allow any metadata write bio to be
+	 * submitted.
+	 *
+	 * This would prevent use-after-free if we had dirty pages not
+	 * cleaned up, which can still happen by fuzzed images.
+	 *
+	 * - Bad extent tree
+	 *   Allowing existing tree block to be allocated for other trees.
+	 *
+	 * - Log tree operations
+	 *   Exiting tree blocks get allocated to log tree, bumps its
+	 *   generation, then get cleaned in tree re-balance.
+	 *   Such tree block will not be written back, since it's clean,
+	 *   thus no WRITTEN flag set.
+	 *   And after log writes back, this tree block is not traced by
+	 *   any dirty extent_io_tree.
+	 *
+	 * - Offending tree block gets re-dirtied from its original owner
+	 *   Since it has bumped generation, no WRITTEN flag, it can be
+	 *   reused without COWing. This tree block will not be traced
+	 *   by btrfs_transaction::dirty_pages.
+	 *
+	 *   Now such dirty tree block will not be cleaned by any dirty
+	 *   extent io tree. Thus we don't want to submit such wild eb
+	 *   if the fs already has error.
+	 *
+	 * We can get ret > 0 from submit_extent_page() indicating how many ebs
+	 * were submitted. Reset it to 0 to avoid false alerts for the caller.
+	 */
+	if (ret > 0)
+		ret = 0;
+	if (!ret && BTRFS_FS_ERROR(fs_info))
+		ret = -EROFS;
+
+	if (ctx.zoned_bg)
+		btrfs_put_block_group(ctx.zoned_bg);
+	btrfs_zoned_meta_io_unlock(fs_info);
+	return ret;
+}
+
+/*
+ * Walk the list of dirty pages of the given address space and write all of them.
+ *
+ * @mapping:   address space structure to write
+ * @wbc:       subtract the number of written pages from *@wbc->nr_to_write
+ * @bio_ctrl:  holds context for the write, namely the bio
+ *
+ * If a page is already under I/O, write_cache_pages() skips it, even
+ * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
+ * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
+ * and msync() need to guarantee that all the data which was dirty at the time
+ * the call was made get new I/O started against them.  If wbc->sync_mode is
+ * WB_SYNC_ALL then we were called for data integrity and we must wait for
+ * existing IO to complete.
+ */
+static int extent_write_cache_pages(struct address_space *mapping,
+			     struct btrfs_bio_ctrl *bio_ctrl)
+{
+	struct writeback_control *wbc = bio_ctrl->wbc;
+	struct inode *inode = mapping->host;
+	int ret = 0;
+	int done = 0;
+	int nr_to_write_done = 0;
+	struct folio_batch fbatch;
+	unsigned int nr_folios;
+	pgoff_t index;
+	pgoff_t end;		/* Inclusive */
+	pgoff_t done_index;
+	int range_whole = 0;
+	int scanned = 0;
+	xa_mark_t tag;
+
+	/*
+	 * We have to hold onto the inode so that ordered extents can do their
+	 * work when the IO finishes.  The alternative to this is failing to add
+	 * an ordered extent if the igrab() fails there and that is a huge pain
+	 * to deal with, so instead just hold onto the inode throughout the
+	 * writepages operation.  If it fails here we are freeing up the inode
+	 * anyway and we'd rather not waste our time writing out stuff that is
+	 * going to be truncated anyway.
+	 */
+	if (!igrab(inode))
+		return 0;
+
+	folio_batch_init(&fbatch);
+	if (wbc->range_cyclic) {
+		index = mapping->writeback_index; /* Start from prev offset */
+		end = -1;
+		/*
+		 * Start from the beginning does not need to cycle over the
+		 * range, mark it as scanned.
+		 */
+		scanned = (index == 0);
+	} else {
+		index = wbc->range_start >> PAGE_SHIFT;
+		end = wbc->range_end >> PAGE_SHIFT;
+		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
+			range_whole = 1;
+		scanned = 1;
+	}
+
+	/*
+	 * We do the tagged writepage as long as the snapshot flush bit is set
+	 * and we are the first one who do the filemap_flush() on this inode.
+	 *
+	 * The nr_to_write == LONG_MAX is needed to make sure other flushers do
+	 * not race in and drop the bit.
+	 */
+	if (range_whole && wbc->nr_to_write == LONG_MAX &&
+	    test_and_clear_bit(BTRFS_INODE_SNAPSHOT_FLUSH,
+			       &BTRFS_I(inode)->runtime_flags))
+		wbc->tagged_writepages = 1;
+
+	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+		tag = PAGECACHE_TAG_TOWRITE;
+	else
+		tag = PAGECACHE_TAG_DIRTY;
+retry:
+	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+		tag_pages_for_writeback(mapping, index, end);
+	done_index = index;
+	while (!done && !nr_to_write_done && (index <= end) &&
+			(nr_folios = filemap_get_folios_tag(mapping, &index,
+							end, tag, &fbatch))) {
+		unsigned i;
+
+		for (i = 0; i < nr_folios; i++) {
+			struct folio *folio = fbatch.folios[i];
+
+			done_index = folio_next_index(folio);
+			/*
+			 * At this point we hold neither the i_pages lock nor
+			 * the page lock: the page may be truncated or
+			 * invalidated (changing page->mapping to NULL),
+			 * or even swizzled back from swapper_space to
+			 * tmpfs file mapping
+			 */
+			if (!folio_trylock(folio)) {
+				submit_write_bio(bio_ctrl, 0);
+				folio_lock(folio);
+			}
+
+			if (unlikely(folio->mapping != mapping)) {
+				folio_unlock(folio);
+				continue;
+			}
+
+			if (!folio_test_dirty(folio)) {
+				/* Someone wrote it for us. */
+				folio_unlock(folio);
+				continue;
+			}
+
+			if (wbc->sync_mode != WB_SYNC_NONE) {
+				if (folio_test_writeback(folio))
+					submit_write_bio(bio_ctrl, 0);
+				folio_wait_writeback(folio);
+			}
+
+			if (folio_test_writeback(folio) ||
+			    !folio_clear_dirty_for_io(folio)) {
+				folio_unlock(folio);
+				continue;
+			}
+
+			ret = __extent_writepage(&folio->page, bio_ctrl);
+			if (ret < 0) {
+				done = 1;
+				break;
+			}
+
+			/*
+			 * The filesystem may choose to bump up nr_to_write.
+			 * We have to make sure to honor the new nr_to_write
+			 * at any time.
+			 */
+			nr_to_write_done = (wbc->sync_mode == WB_SYNC_NONE &&
+					    wbc->nr_to_write <= 0);
+		}
+		folio_batch_release(&fbatch);
+		cond_resched();
+	}
+	if (!scanned && !done) {
+		/*
+		 * We hit the last page and there is more work to be done: wrap
+		 * back to the start of the file
+		 */
+		scanned = 1;
+		index = 0;
+
+		/*
+		 * If we're looping we could run into a page that is locked by a
+		 * writer and that writer could be waiting on writeback for a
+		 * page in our current bio, and thus deadlock, so flush the
+		 * write bio here.
+		 */
+		submit_write_bio(bio_ctrl, 0);
+		goto retry;
+	}
+
+	if (wbc->range_cyclic || (wbc->nr_to_write > 0 && range_whole))
+		mapping->writeback_index = done_index;
+
+	btrfs_add_delayed_iput(BTRFS_I(inode));
+	return ret;
+}
+
+/*
+ * Submit the pages in the range to bio for call sites which delalloc range has
+ * already been ran (aka, ordered extent inserted) and all pages are still
+ * locked.
+ */
+void extent_write_locked_range(struct inode *inode, struct page *locked_page,
+			       u64 start, u64 end, struct writeback_control *wbc,
+			       bool pages_dirty)
+{
+	bool found_error = false;
+	int ret = 0;
+	struct address_space *mapping = inode->i_mapping;
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	const u32 sectorsize = fs_info->sectorsize;
+	loff_t i_size = i_size_read(inode);
+	u64 cur = start;
+	struct btrfs_bio_ctrl bio_ctrl = {
+		.wbc = wbc,
+		.opf = REQ_OP_WRITE | wbc_to_write_flags(wbc),
+	};
+
+	if (wbc->no_cgroup_owner)
+		bio_ctrl.opf |= REQ_BTRFS_CGROUP_PUNT;
+
+	ASSERT(IS_ALIGNED(start, sectorsize) && IS_ALIGNED(end + 1, sectorsize));
+
+	while (cur <= end) {
+		u64 cur_end = min(round_down(cur, PAGE_SIZE) + PAGE_SIZE - 1, end);
+		u32 cur_len = cur_end + 1 - cur;
+		struct page *page;
+		int nr = 0;
+
+		page = find_get_page(mapping, cur >> PAGE_SHIFT);
+		ASSERT(PageLocked(page));
+		if (pages_dirty && page != locked_page) {
+			ASSERT(PageDirty(page));
+			clear_page_dirty_for_io(page);
+		}
+
+		ret = __extent_writepage_io(BTRFS_I(inode), page, &bio_ctrl,
+					    i_size, &nr);
+		if (ret == 1)
+			goto next_page;
+
+		/* Make sure the mapping tag for page dirty gets cleared. */
+		if (nr == 0) {
+			set_page_writeback(page);
+			end_page_writeback(page);
+		}
+		if (ret) {
+			btrfs_mark_ordered_io_finished(BTRFS_I(inode), page,
+						       cur, cur_len, !ret);
+			mapping_set_error(page->mapping, ret);
+		}
+		btrfs_page_unlock_writer(fs_info, page, cur, cur_len);
+		if (ret < 0)
+			found_error = true;
+next_page:
+		put_page(page);
+		cur = cur_end + 1;
+	}
+
+	submit_write_bio(&bio_ctrl, found_error ? ret : 0);
+}
+
+int extent_writepages(struct address_space *mapping,
+		      struct writeback_control *wbc)
+{
+	struct inode *inode = mapping->host;
+	int ret = 0;
+	struct btrfs_bio_ctrl bio_ctrl = {
+		.wbc = wbc,
+		.opf = REQ_OP_WRITE | wbc_to_write_flags(wbc),
+	};
+
+	/*
+	 * Allow only a single thread to do the reloc work in zoned mode to
+	 * protect the write pointer updates.
+	 */
+	btrfs_zoned_data_reloc_lock(BTRFS_I(inode));
+	ret = extent_write_cache_pages(mapping, &bio_ctrl);
+	submit_write_bio(&bio_ctrl, ret);
+	btrfs_zoned_data_reloc_unlock(BTRFS_I(inode));
+	return ret;
+}
+
+void extent_readahead(struct readahead_control *rac)
+{
+	struct btrfs_bio_ctrl bio_ctrl = { .opf = REQ_OP_READ | REQ_RAHEAD };
+	struct page *pagepool[16];
+	struct extent_map *em_cached = NULL;
+	u64 prev_em_start = (u64)-1;
+	int nr;
+
+	while ((nr = readahead_page_batch(rac, pagepool))) {
+		u64 contig_start = readahead_pos(rac);
+		u64 contig_end = contig_start + readahead_batch_length(rac) - 1;
+
+		contiguous_readpages(pagepool, nr, contig_start, contig_end,
+				&em_cached, &bio_ctrl, &prev_em_start);
+	}
+
+	if (em_cached)
+		free_extent_map(em_cached);
+	submit_one_bio(&bio_ctrl);
+}
+
+/*
+ * basic invalidate_folio code, this waits on any locked or writeback
+ * ranges corresponding to the folio, and then deletes any extent state
+ * records from the tree
+ */
+int extent_invalidate_folio(struct extent_io_tree *tree,
+			  struct folio *folio, size_t offset)
+{
+	struct extent_state *cached_state = NULL;
+	u64 start = folio_pos(folio);
+	u64 end = start + folio_size(folio) - 1;
+	size_t blocksize = folio->mapping->host->i_sb->s_blocksize;
+
+	/* This function is only called for the btree inode */
+	ASSERT(tree->owner == IO_TREE_BTREE_INODE_IO);
+
+	start += ALIGN(offset, blocksize);
+	if (start > end)
+		return 0;
+
+	lock_extent(tree, start, end, &cached_state);
+	folio_wait_writeback(folio);
+
+	/*
+	 * Currently for btree io tree, only EXTENT_LOCKED is utilized,
+	 * so here we only need to unlock the extent range to free any
+	 * existing extent state.
+	 */
+	unlock_extent(tree, start, end, &cached_state);
+	return 0;
+}
+
+/*
+ * a helper for release_folio, this tests for areas of the page that
+ * are locked or under IO and drops the related state bits if it is safe
+ * to drop the page.
+ */
+static int try_release_extent_state(struct extent_io_tree *tree,
+				    struct page *page, gfp_t mask)
+{
+	u64 start = page_offset(page);
+	u64 end = start + PAGE_SIZE - 1;
+	int ret = 1;
+
+	if (test_range_bit(tree, start, end, EXTENT_LOCKED, 0, NULL)) {
+		ret = 0;
+	} else {
+		u32 clear_bits = ~(EXTENT_LOCKED | EXTENT_NODATASUM |
+				   EXTENT_DELALLOC_NEW | EXTENT_CTLBITS |
+				   EXTENT_QGROUP_RESERVED);
+
+		/*
+		 * At this point we can safely clear everything except the
+		 * locked bit, the nodatasum bit and the delalloc new bit.
+		 * The delalloc new bit will be cleared by ordered extent
+		 * completion.
+		 */
+		ret = __clear_extent_bit(tree, start, end, clear_bits, NULL, NULL);
+
+		/* if clear_extent_bit failed for enomem reasons,
+		 * we can't allow the release to continue.
+		 */
+		if (ret < 0)
+			ret = 0;
+		else
+			ret = 1;
+	}
+	return ret;
+}
+
+/*
+ * a helper for release_folio.  As long as there are no locked extents
+ * in the range corresponding to the page, both state records and extent
+ * map records are removed
+ */
+int try_release_extent_mapping(struct page *page, gfp_t mask)
+{
+	struct extent_map *em;
+	u64 start = page_offset(page);
+	u64 end = start + PAGE_SIZE - 1;
+	struct btrfs_inode *btrfs_inode = BTRFS_I(page->mapping->host);
+	struct extent_io_tree *tree = &btrfs_inode->io_tree;
+	struct extent_map_tree *map = &btrfs_inode->extent_tree;
+
+	if (gfpflags_allow_blocking(mask) &&
+	    page->mapping->host->i_size > SZ_16M) {
+		u64 len;
+		while (start <= end) {
+			struct btrfs_fs_info *fs_info;
+			u64 cur_gen;
+
+			len = end - start + 1;
+			write_lock(&map->lock);
+			em = lookup_extent_mapping(map, start, len);
+			if (!em) {
+				write_unlock(&map->lock);
+				break;
+			}
+			if (test_bit(EXTENT_FLAG_PINNED, &em->flags) ||
+			    em->start != start) {
+				write_unlock(&map->lock);
+				free_extent_map(em);
+				break;
+			}
+			if (test_range_bit(tree, em->start,
+					   extent_map_end(em) - 1,
+					   EXTENT_LOCKED, 0, NULL))
+				goto next;
+			/*
+			 * If it's not in the list of modified extents, used
+			 * by a fast fsync, we can remove it. If it's being
+			 * logged we can safely remove it since fsync took an
+			 * extra reference on the em.
+			 */
+			if (list_empty(&em->list) ||
+			    test_bit(EXTENT_FLAG_LOGGING, &em->flags))
+				goto remove_em;
+			/*
+			 * If it's in the list of modified extents, remove it
+			 * only if its generation is older then the current one,
+			 * in which case we don't need it for a fast fsync.
+			 * Otherwise don't remove it, we could be racing with an
+			 * ongoing fast fsync that could miss the new extent.
+			 */
+			fs_info = btrfs_inode->root->fs_info;
+			spin_lock(&fs_info->trans_lock);
+			cur_gen = fs_info->generation;
+			spin_unlock(&fs_info->trans_lock);
+			if (em->generation >= cur_gen)
+				goto next;
+remove_em:
+			/*
+			 * We only remove extent maps that are not in the list of
+			 * modified extents or that are in the list but with a
+			 * generation lower then the current generation, so there
+			 * is no need to set the full fsync flag on the inode (it
+			 * hurts the fsync performance for workloads with a data
+			 * size that exceeds or is close to the system's memory).
+			 */
+			remove_extent_mapping(map, em);
+			/* once for the rb tree */
+			free_extent_map(em);
+next:
+			start = extent_map_end(em);
+			write_unlock(&map->lock);
+
+			/* once for us */
+			free_extent_map(em);
+
+			cond_resched(); /* Allow large-extent preemption. */
+		}
+	}
+	return try_release_extent_state(tree, page, mask);
+}
+
+/*
+ * To cache previous fiemap extent
+ *
+ * Will be used for merging fiemap extent
+ */
+struct fiemap_cache {
+	u64 offset;
+	u64 phys;
+	u64 len;
+	u32 flags;
+	bool cached;
+};
+
+/*
+ * Helper to submit fiemap extent.
+ *
+ * Will try to merge current fiemap extent specified by @offset, @phys,
+ * @len and @flags with cached one.
+ * And only when we fails to merge, cached one will be submitted as
+ * fiemap extent.
+ *
+ * Return value is the same as fiemap_fill_next_extent().
+ */
+static int emit_fiemap_extent(struct fiemap_extent_info *fieinfo,
+				struct fiemap_cache *cache,
+				u64 offset, u64 phys, u64 len, u32 flags)
+{
+	int ret = 0;
+
+	/* Set at the end of extent_fiemap(). */
+	ASSERT((flags & FIEMAP_EXTENT_LAST) == 0);
+
+	if (!cache->cached)
+		goto assign;
+
+	/*
+	 * Sanity check, extent_fiemap() should have ensured that new
+	 * fiemap extent won't overlap with cached one.
+	 * Not recoverable.
+	 *
+	 * NOTE: Physical address can overlap, due to compression
+	 */
+	if (cache->offset + cache->len > offset) {
+		WARN_ON(1);
+		return -EINVAL;
+	}
+
+	/*
+	 * Only merges fiemap extents if
+	 * 1) Their logical addresses are continuous
+	 *
+	 * 2) Their physical addresses are continuous
+	 *    So truly compressed (physical size smaller than logical size)
+	 *    extents won't get merged with each other
+	 *
+	 * 3) Share same flags
+	 */
+	if (cache->offset + cache->len  == offset &&
+	    cache->phys + cache->len == phys  &&
+	    cache->flags == flags) {
+		cache->len += len;
+		return 0;
+	}
+
+	/* Not mergeable, need to submit cached one */
+	ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
+				      cache->len, cache->flags);
+	cache->cached = false;
+	if (ret)
+		return ret;
+assign:
+	cache->cached = true;
+	cache->offset = offset;
+	cache->phys = phys;
+	cache->len = len;
+	cache->flags = flags;
+
+	return 0;
+}
+
+/*
+ * Emit last fiemap cache
+ *
+ * The last fiemap cache may still be cached in the following case:
+ * 0		      4k		    8k
+ * |<- Fiemap range ->|
+ * |<------------  First extent ----------->|
+ *
+ * In this case, the first extent range will be cached but not emitted.
+ * So we must emit it before ending extent_fiemap().
+ */
+static int emit_last_fiemap_cache(struct fiemap_extent_info *fieinfo,
+				  struct fiemap_cache *cache)
+{
+	int ret;
+
+	if (!cache->cached)
+		return 0;
+
+	ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
+				      cache->len, cache->flags);
+	cache->cached = false;
+	if (ret > 0)
+		ret = 0;
+	return ret;
+}
+
+static int fiemap_next_leaf_item(struct btrfs_inode *inode, struct btrfs_path *path)
+{
+	struct extent_buffer *clone;
+	struct btrfs_key key;
+	int slot;
+	int ret;
+
+	path->slots[0]++;
+	if (path->slots[0] < btrfs_header_nritems(path->nodes[0]))
+		return 0;
+
+	ret = btrfs_next_leaf(inode->root, path);
+	if (ret != 0)
+		return ret;
+
+	/*
+	 * Don't bother with cloning if there are no more file extent items for
+	 * our inode.
+	 */
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+	if (key.objectid != btrfs_ino(inode) || key.type != BTRFS_EXTENT_DATA_KEY)
+		return 1;
+
+	/* See the comment at fiemap_search_slot() about why we clone. */
+	clone = btrfs_clone_extent_buffer(path->nodes[0]);
+	if (!clone)
+		return -ENOMEM;
+
+	slot = path->slots[0];
+	btrfs_release_path(path);
+	path->nodes[0] = clone;
+	path->slots[0] = slot;
+
+	return 0;
+}
+
+/*
+ * Search for the first file extent item that starts at a given file offset or
+ * the one that starts immediately before that offset.
+ * Returns: 0 on success, < 0 on error, 1 if not found.
+ */
+static int fiemap_search_slot(struct btrfs_inode *inode, struct btrfs_path *path,
+			      u64 file_offset)
+{
+	const u64 ino = btrfs_ino(inode);
+	struct btrfs_root *root = inode->root;
+	struct extent_buffer *clone;
+	struct btrfs_key key;
+	int slot;
+	int ret;
+
+	key.objectid = ino;
+	key.type = BTRFS_EXTENT_DATA_KEY;
+	key.offset = file_offset;
+
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0)
+		return ret;
+
+	if (ret > 0 && path->slots[0] > 0) {
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0] - 1);
+		if (key.objectid == ino && key.type == BTRFS_EXTENT_DATA_KEY)
+			path->slots[0]--;
+	}
+
+	if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
+		ret = btrfs_next_leaf(root, path);
+		if (ret != 0)
+			return ret;
+
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+		if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
+			return 1;
+	}
+
+	/*
+	 * We clone the leaf and use it during fiemap. This is because while
+	 * using the leaf we do expensive things like checking if an extent is
+	 * shared, which can take a long time. In order to prevent blocking
+	 * other tasks for too long, we use a clone of the leaf. We have locked
+	 * the file range in the inode's io tree, so we know none of our file
+	 * extent items can change. This way we avoid blocking other tasks that
+	 * want to insert items for other inodes in the same leaf or b+tree
+	 * rebalance operations (triggered for example when someone is trying
+	 * to push items into this leaf when trying to insert an item in a
+	 * neighbour leaf).
+	 * We also need the private clone because holding a read lock on an
+	 * extent buffer of the subvolume's b+tree will make lockdep unhappy
+	 * when we call fiemap_fill_next_extent(), because that may cause a page
+	 * fault when filling the user space buffer with fiemap data.
+	 */
+	clone = btrfs_clone_extent_buffer(path->nodes[0]);
+	if (!clone)
+		return -ENOMEM;
+
+	slot = path->slots[0];
+	btrfs_release_path(path);
+	path->nodes[0] = clone;
+	path->slots[0] = slot;
+
+	return 0;
+}
+
+/*
+ * Process a range which is a hole or a prealloc extent in the inode's subvolume
+ * btree. If @disk_bytenr is 0, we are dealing with a hole, otherwise a prealloc
+ * extent. The end offset (@end) is inclusive.
+ */
+static int fiemap_process_hole(struct btrfs_inode *inode,
+			       struct fiemap_extent_info *fieinfo,
+			       struct fiemap_cache *cache,
+			       struct extent_state **delalloc_cached_state,
+			       struct btrfs_backref_share_check_ctx *backref_ctx,
+			       u64 disk_bytenr, u64 extent_offset,
+			       u64 extent_gen,
+			       u64 start, u64 end)
+{
+	const u64 i_size = i_size_read(&inode->vfs_inode);
+	u64 cur_offset = start;
+	u64 last_delalloc_end = 0;
+	u32 prealloc_flags = FIEMAP_EXTENT_UNWRITTEN;
+	bool checked_extent_shared = false;
+	int ret;
+
+	/*
+	 * There can be no delalloc past i_size, so don't waste time looking for
+	 * it beyond i_size.
+	 */
+	while (cur_offset < end && cur_offset < i_size) {
+		u64 delalloc_start;
+		u64 delalloc_end;
+		u64 prealloc_start;
+		u64 prealloc_len = 0;
+		bool delalloc;
+
+		delalloc = btrfs_find_delalloc_in_range(inode, cur_offset, end,
+							delalloc_cached_state,
+							&delalloc_start,
+							&delalloc_end);
+		if (!delalloc)
+			break;
+
+		/*
+		 * If this is a prealloc extent we have to report every section
+		 * of it that has no delalloc.
+		 */
+		if (disk_bytenr != 0) {
+			if (last_delalloc_end == 0) {
+				prealloc_start = start;
+				prealloc_len = delalloc_start - start;
+			} else {
+				prealloc_start = last_delalloc_end + 1;
+				prealloc_len = delalloc_start - prealloc_start;
+			}
+		}
+
+		if (prealloc_len > 0) {
+			if (!checked_extent_shared && fieinfo->fi_extents_max) {
+				ret = btrfs_is_data_extent_shared(inode,
+								  disk_bytenr,
+								  extent_gen,
+								  backref_ctx);
+				if (ret < 0)
+					return ret;
+				else if (ret > 0)
+					prealloc_flags |= FIEMAP_EXTENT_SHARED;
+
+				checked_extent_shared = true;
+			}
+			ret = emit_fiemap_extent(fieinfo, cache, prealloc_start,
+						 disk_bytenr + extent_offset,
+						 prealloc_len, prealloc_flags);
+			if (ret)
+				return ret;
+			extent_offset += prealloc_len;
+		}
+
+		ret = emit_fiemap_extent(fieinfo, cache, delalloc_start, 0,
+					 delalloc_end + 1 - delalloc_start,
+					 FIEMAP_EXTENT_DELALLOC |
+					 FIEMAP_EXTENT_UNKNOWN);
+		if (ret)
+			return ret;
+
+		last_delalloc_end = delalloc_end;
+		cur_offset = delalloc_end + 1;
+		extent_offset += cur_offset - delalloc_start;
+		cond_resched();
+	}
+
+	/*
+	 * Either we found no delalloc for the whole prealloc extent or we have
+	 * a prealloc extent that spans i_size or starts at or after i_size.
+	 */
+	if (disk_bytenr != 0 && last_delalloc_end < end) {
+		u64 prealloc_start;
+		u64 prealloc_len;
+
+		if (last_delalloc_end == 0) {
+			prealloc_start = start;
+			prealloc_len = end + 1 - start;
+		} else {
+			prealloc_start = last_delalloc_end + 1;
+			prealloc_len = end + 1 - prealloc_start;
+		}
+
+		if (!checked_extent_shared && fieinfo->fi_extents_max) {
+			ret = btrfs_is_data_extent_shared(inode,
+							  disk_bytenr,
+							  extent_gen,
+							  backref_ctx);
+			if (ret < 0)
+				return ret;
+			else if (ret > 0)
+				prealloc_flags |= FIEMAP_EXTENT_SHARED;
+		}
+		ret = emit_fiemap_extent(fieinfo, cache, prealloc_start,
+					 disk_bytenr + extent_offset,
+					 prealloc_len, prealloc_flags);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int fiemap_find_last_extent_offset(struct btrfs_inode *inode,
+					  struct btrfs_path *path,
+					  u64 *last_extent_end_ret)
+{
+	const u64 ino = btrfs_ino(inode);
+	struct btrfs_root *root = inode->root;
+	struct extent_buffer *leaf;
+	struct btrfs_file_extent_item *ei;
+	struct btrfs_key key;
+	u64 disk_bytenr;
+	int ret;
+
+	/*
+	 * Lookup the last file extent. We're not using i_size here because
+	 * there might be preallocation past i_size.
+	 */
+	ret = btrfs_lookup_file_extent(NULL, root, path, ino, (u64)-1, 0);
+	/* There can't be a file extent item at offset (u64)-1 */
+	ASSERT(ret != 0);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * For a non-existing key, btrfs_search_slot() always leaves us at a
+	 * slot > 0, except if the btree is empty, which is impossible because
+	 * at least it has the inode item for this inode and all the items for
+	 * the root inode 256.
+	 */
+	ASSERT(path->slots[0] > 0);
+	path->slots[0]--;
+	leaf = path->nodes[0];
+	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+	if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY) {
+		/* No file extent items in the subvolume tree. */
+		*last_extent_end_ret = 0;
+		return 0;
+	}
+
+	/*
+	 * For an inline extent, the disk_bytenr is where inline data starts at,
+	 * so first check if we have an inline extent item before checking if we
+	 * have an implicit hole (disk_bytenr == 0).
+	 */
+	ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
+	if (btrfs_file_extent_type(leaf, ei) == BTRFS_FILE_EXTENT_INLINE) {
+		*last_extent_end_ret = btrfs_file_extent_end(path);
+		return 0;
+	}
+
+	/*
+	 * Find the last file extent item that is not a hole (when NO_HOLES is
+	 * not enabled). This should take at most 2 iterations in the worst
+	 * case: we have one hole file extent item at slot 0 of a leaf and
+	 * another hole file extent item as the last item in the previous leaf.
+	 * This is because we merge file extent items that represent holes.
+	 */
+	disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
+	while (disk_bytenr == 0) {
+		ret = btrfs_previous_item(root, path, ino, BTRFS_EXTENT_DATA_KEY);
+		if (ret < 0) {
+			return ret;
+		} else if (ret > 0) {
+			/* No file extent items that are not holes. */
+			*last_extent_end_ret = 0;
+			return 0;
+		}
+		leaf = path->nodes[0];
+		ei = btrfs_item_ptr(leaf, path->slots[0],
+				    struct btrfs_file_extent_item);
+		disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
+	}
+
+	*last_extent_end_ret = btrfs_file_extent_end(path);
+	return 0;
+}
+
+int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
+		  u64 start, u64 len)
+{
+	const u64 ino = btrfs_ino(inode);
+	struct extent_state *cached_state = NULL;
+	struct extent_state *delalloc_cached_state = NULL;
+	struct btrfs_path *path;
+	struct fiemap_cache cache = { 0 };
+	struct btrfs_backref_share_check_ctx *backref_ctx;
+	u64 last_extent_end;
+	u64 prev_extent_end;
+	u64 lockstart;
+	u64 lockend;
+	bool stopped = false;
+	int ret;
+
+	backref_ctx = btrfs_alloc_backref_share_check_ctx();
+	path = btrfs_alloc_path();
+	if (!backref_ctx || !path) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	lockstart = round_down(start, inode->root->fs_info->sectorsize);
+	lockend = round_up(start + len, inode->root->fs_info->sectorsize);
+	prev_extent_end = lockstart;
+
+	btrfs_inode_lock(inode, BTRFS_ILOCK_SHARED);
+	lock_extent(&inode->io_tree, lockstart, lockend, &cached_state);
+
+	ret = fiemap_find_last_extent_offset(inode, path, &last_extent_end);
+	if (ret < 0)
+		goto out_unlock;
+	btrfs_release_path(path);
+
+	path->reada = READA_FORWARD;
+	ret = fiemap_search_slot(inode, path, lockstart);
+	if (ret < 0) {
+		goto out_unlock;
+	} else if (ret > 0) {
+		/*
+		 * No file extent item found, but we may have delalloc between
+		 * the current offset and i_size. So check for that.
+		 */
+		ret = 0;
+		goto check_eof_delalloc;
+	}
+
+	while (prev_extent_end < lockend) {
+		struct extent_buffer *leaf = path->nodes[0];
+		struct btrfs_file_extent_item *ei;
+		struct btrfs_key key;
+		u64 extent_end;
+		u64 extent_len;
+		u64 extent_offset = 0;
+		u64 extent_gen;
+		u64 disk_bytenr = 0;
+		u64 flags = 0;
+		int extent_type;
+		u8 compression;
+
+		btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+		if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
+			break;
+
+		extent_end = btrfs_file_extent_end(path);
+
+		/*
+		 * The first iteration can leave us at an extent item that ends
+		 * before our range's start. Move to the next item.
+		 */
+		if (extent_end <= lockstart)
+			goto next_item;
+
+		backref_ctx->curr_leaf_bytenr = leaf->start;
+
+		/* We have in implicit hole (NO_HOLES feature enabled). */
+		if (prev_extent_end < key.offset) {
+			const u64 range_end = min(key.offset, lockend) - 1;
+
+			ret = fiemap_process_hole(inode, fieinfo, &cache,
+						  &delalloc_cached_state,
+						  backref_ctx, 0, 0, 0,
+						  prev_extent_end, range_end);
+			if (ret < 0) {
+				goto out_unlock;
+			} else if (ret > 0) {
+				/* fiemap_fill_next_extent() told us to stop. */
+				stopped = true;
+				break;
+			}
+
+			/* We've reached the end of the fiemap range, stop. */
+			if (key.offset >= lockend) {
+				stopped = true;
+				break;
+			}
+		}
+
+		extent_len = extent_end - key.offset;
+		ei = btrfs_item_ptr(leaf, path->slots[0],
+				    struct btrfs_file_extent_item);
+		compression = btrfs_file_extent_compression(leaf, ei);
+		extent_type = btrfs_file_extent_type(leaf, ei);
+		extent_gen = btrfs_file_extent_generation(leaf, ei);
+
+		if (extent_type != BTRFS_FILE_EXTENT_INLINE) {
+			disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
+			if (compression == BTRFS_COMPRESS_NONE)
+				extent_offset = btrfs_file_extent_offset(leaf, ei);
+		}
+
+		if (compression != BTRFS_COMPRESS_NONE)
+			flags |= FIEMAP_EXTENT_ENCODED;
+
+		if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
+			flags |= FIEMAP_EXTENT_DATA_INLINE;
+			flags |= FIEMAP_EXTENT_NOT_ALIGNED;
+			ret = emit_fiemap_extent(fieinfo, &cache, key.offset, 0,
+						 extent_len, flags);
+		} else if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
+			ret = fiemap_process_hole(inode, fieinfo, &cache,
+						  &delalloc_cached_state,
+						  backref_ctx,
+						  disk_bytenr, extent_offset,
+						  extent_gen, key.offset,
+						  extent_end - 1);
+		} else if (disk_bytenr == 0) {
+			/* We have an explicit hole. */
+			ret = fiemap_process_hole(inode, fieinfo, &cache,
+						  &delalloc_cached_state,
+						  backref_ctx, 0, 0, 0,
+						  key.offset, extent_end - 1);
+		} else {
+			/* We have a regular extent. */
+			if (fieinfo->fi_extents_max) {
+				ret = btrfs_is_data_extent_shared(inode,
+								  disk_bytenr,
+								  extent_gen,
+								  backref_ctx);
+				if (ret < 0)
+					goto out_unlock;
+				else if (ret > 0)
+					flags |= FIEMAP_EXTENT_SHARED;
+			}
+
+			ret = emit_fiemap_extent(fieinfo, &cache, key.offset,
+						 disk_bytenr + extent_offset,
+						 extent_len, flags);
+		}
+
+		if (ret < 0) {
+			goto out_unlock;
+		} else if (ret > 0) {
+			/* fiemap_fill_next_extent() told us to stop. */
+			stopped = true;
+			break;
+		}
+
+		prev_extent_end = extent_end;
+next_item:
+		if (fatal_signal_pending(current)) {
+			ret = -EINTR;
+			goto out_unlock;
+		}
+
+		ret = fiemap_next_leaf_item(inode, path);
+		if (ret < 0) {
+			goto out_unlock;
+		} else if (ret > 0) {
+			/* No more file extent items for this inode. */
+			break;
+		}
+		cond_resched();
+	}
+
+check_eof_delalloc:
+	/*
+	 * Release (and free) the path before emitting any final entries to
+	 * fiemap_fill_next_extent() to keep lockdep happy. This is because
+	 * once we find no more file extent items exist, we may have a
+	 * non-cloned leaf, and fiemap_fill_next_extent() can trigger page
+	 * faults when copying data to the user space buffer.
+	 */
+	btrfs_free_path(path);
+	path = NULL;
+
+	if (!stopped && prev_extent_end < lockend) {
+		ret = fiemap_process_hole(inode, fieinfo, &cache,
+					  &delalloc_cached_state, backref_ctx,
+					  0, 0, 0, prev_extent_end, lockend - 1);
+		if (ret < 0)
+			goto out_unlock;
+		prev_extent_end = lockend;
+	}
+
+	if (cache.cached && cache.offset + cache.len >= last_extent_end) {
+		const u64 i_size = i_size_read(&inode->vfs_inode);
+
+		if (prev_extent_end < i_size) {
+			u64 delalloc_start;
+			u64 delalloc_end;
+			bool delalloc;
+
+			delalloc = btrfs_find_delalloc_in_range(inode,
+								prev_extent_end,
+								i_size - 1,
+								&delalloc_cached_state,
+								&delalloc_start,
+								&delalloc_end);
+			if (!delalloc)
+				cache.flags |= FIEMAP_EXTENT_LAST;
+		} else {
+			cache.flags |= FIEMAP_EXTENT_LAST;
+		}
+	}
+
+	ret = emit_last_fiemap_cache(fieinfo, &cache);
+
+out_unlock:
+	unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);
+	btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
+out:
+	free_extent_state(delalloc_cached_state);
+	btrfs_free_backref_share_ctx(backref_ctx);
+	btrfs_free_path(path);
+	return ret;
+}
+
+static void __free_extent_buffer(struct extent_buffer *eb)
+{
+	kmem_cache_free(extent_buffer_cache, eb);
+}
+
+static int extent_buffer_under_io(const struct extent_buffer *eb)
+{
+	return (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
+		test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+}
+
+static bool page_range_has_eb(struct btrfs_fs_info *fs_info, struct page *page)
+{
+	struct btrfs_subpage *subpage;
+
+	lockdep_assert_held(&page->mapping->private_lock);
+
+	if (PagePrivate(page)) {
+		subpage = (struct btrfs_subpage *)page->private;
+		if (atomic_read(&subpage->eb_refs))
+			return true;
+		/*
+		 * Even there is no eb refs here, we may still have
+		 * end_page_read() call relying on page::private.
+		 */
+		if (atomic_read(&subpage->readers))
+			return true;
+	}
+	return false;
+}
+
+static void detach_extent_buffer_page(struct extent_buffer *eb, struct page *page)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	const bool mapped = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
+
+	/*
+	 * For mapped eb, we're going to change the page private, which should
+	 * be done under the private_lock.
+	 */
+	if (mapped)
+		spin_lock(&page->mapping->private_lock);
+
+	if (!PagePrivate(page)) {
+		if (mapped)
+			spin_unlock(&page->mapping->private_lock);
+		return;
+	}
+
+	if (fs_info->nodesize >= PAGE_SIZE) {
+		/*
+		 * We do this since we'll remove the pages after we've
+		 * removed the eb from the radix tree, so we could race
+		 * and have this page now attached to the new eb.  So
+		 * only clear page_private if it's still connected to
+		 * this eb.
+		 */
+		if (PagePrivate(page) &&
+		    page->private == (unsigned long)eb) {
+			BUG_ON(test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+			BUG_ON(PageDirty(page));
+			BUG_ON(PageWriteback(page));
+			/*
+			 * We need to make sure we haven't be attached
+			 * to a new eb.
+			 */
+			detach_page_private(page);
+		}
+		if (mapped)
+			spin_unlock(&page->mapping->private_lock);
+		return;
+	}
+
+	/*
+	 * For subpage, we can have dummy eb with page private.  In this case,
+	 * we can directly detach the private as such page is only attached to
+	 * one dummy eb, no sharing.
+	 */
+	if (!mapped) {
+		btrfs_detach_subpage(fs_info, page);
+		return;
+	}
+
+	btrfs_page_dec_eb_refs(fs_info, page);
+
+	/*
+	 * We can only detach the page private if there are no other ebs in the
+	 * page range and no unfinished IO.
+	 */
+	if (!page_range_has_eb(fs_info, page))
+		btrfs_detach_subpage(fs_info, page);
+
+	spin_unlock(&page->mapping->private_lock);
+}
+
+/* Release all pages attached to the extent buffer */
+static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
+{
+	int i;
+	int num_pages;
+
+	ASSERT(!extent_buffer_under_io(eb));
+
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++) {
+		struct page *page = eb->pages[i];
+
+		if (!page)
+			continue;
+
+		detach_extent_buffer_page(eb, page);
+
+		/* One for when we allocated the page */
+		put_page(page);
+	}
+}
+
+/*
+ * Helper for releasing the extent buffer.
+ */
+static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
+{
+	btrfs_release_extent_buffer_pages(eb);
+	btrfs_leak_debug_del_eb(eb);
+	__free_extent_buffer(eb);
+}
+
+static struct extent_buffer *
+__alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
+		      unsigned long len)
+{
+	struct extent_buffer *eb = NULL;
+
+	eb = kmem_cache_zalloc(extent_buffer_cache, GFP_NOFS|__GFP_NOFAIL);
+	eb->start = start;
+	eb->len = len;
+	eb->fs_info = fs_info;
+	init_rwsem(&eb->lock);
+
+	btrfs_leak_debug_add_eb(eb);
+
+	spin_lock_init(&eb->refs_lock);
+	atomic_set(&eb->refs, 1);
+
+	ASSERT(len <= BTRFS_MAX_METADATA_BLOCKSIZE);
+
+	return eb;
+}
+
+struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src)
+{
+	int i;
+	struct extent_buffer *new;
+	int num_pages = num_extent_pages(src);
+	int ret;
+
+	new = __alloc_extent_buffer(src->fs_info, src->start, src->len);
+	if (new == NULL)
+		return NULL;
+
+	/*
+	 * Set UNMAPPED before calling btrfs_release_extent_buffer(), as
+	 * btrfs_release_extent_buffer() have different behavior for
+	 * UNMAPPED subpage extent buffer.
+	 */
+	set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags);
+
+	ret = btrfs_alloc_page_array(num_pages, new->pages);
+	if (ret) {
+		btrfs_release_extent_buffer(new);
+		return NULL;
+	}
+
+	for (i = 0; i < num_pages; i++) {
+		int ret;
+		struct page *p = new->pages[i];
+
+		ret = attach_extent_buffer_page(new, p, NULL);
+		if (ret < 0) {
+			btrfs_release_extent_buffer(new);
+			return NULL;
+		}
+		WARN_ON(PageDirty(p));
+	}
+	copy_extent_buffer_full(new, src);
+	set_extent_buffer_uptodate(new);
+
+	return new;
+}
+
+struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
+						  u64 start, unsigned long len)
+{
+	struct extent_buffer *eb;
+	int num_pages;
+	int i;
+	int ret;
+
+	eb = __alloc_extent_buffer(fs_info, start, len);
+	if (!eb)
+		return NULL;
+
+	num_pages = num_extent_pages(eb);
+	ret = btrfs_alloc_page_array(num_pages, eb->pages);
+	if (ret)
+		goto err;
+
+	for (i = 0; i < num_pages; i++) {
+		struct page *p = eb->pages[i];
+
+		ret = attach_extent_buffer_page(eb, p, NULL);
+		if (ret < 0)
+			goto err;
+	}
+
+	set_extent_buffer_uptodate(eb);
+	btrfs_set_header_nritems(eb, 0);
+	set_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
+
+	return eb;
+err:
+	for (i = 0; i < num_pages; i++) {
+		if (eb->pages[i]) {
+			detach_extent_buffer_page(eb, eb->pages[i]);
+			__free_page(eb->pages[i]);
+		}
+	}
+	__free_extent_buffer(eb);
+	return NULL;
+}
+
+struct extent_buffer *alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
+						u64 start)
+{
+	return __alloc_dummy_extent_buffer(fs_info, start, fs_info->nodesize);
+}
+
+static void check_buffer_tree_ref(struct extent_buffer *eb)
+{
+	int refs;
+	/*
+	 * The TREE_REF bit is first set when the extent_buffer is added
+	 * to the radix tree. It is also reset, if unset, when a new reference
+	 * is created by find_extent_buffer.
+	 *
+	 * It is only cleared in two cases: freeing the last non-tree
+	 * reference to the extent_buffer when its STALE bit is set or
+	 * calling release_folio when the tree reference is the only reference.
+	 *
+	 * In both cases, care is taken to ensure that the extent_buffer's
+	 * pages are not under io. However, release_folio can be concurrently
+	 * called with creating new references, which is prone to race
+	 * conditions between the calls to check_buffer_tree_ref in those
+	 * codepaths and clearing TREE_REF in try_release_extent_buffer.
+	 *
+	 * The actual lifetime of the extent_buffer in the radix tree is
+	 * adequately protected by the refcount, but the TREE_REF bit and
+	 * its corresponding reference are not. To protect against this
+	 * class of races, we call check_buffer_tree_ref from the codepaths
+	 * which trigger io. Note that once io is initiated, TREE_REF can no
+	 * longer be cleared, so that is the moment at which any such race is
+	 * best fixed.
+	 */
+	refs = atomic_read(&eb->refs);
+	if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
+		return;
+
+	spin_lock(&eb->refs_lock);
+	if (!test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
+		atomic_inc(&eb->refs);
+	spin_unlock(&eb->refs_lock);
+}
+
+static void mark_extent_buffer_accessed(struct extent_buffer *eb,
+		struct page *accessed)
+{
+	int num_pages, i;
+
+	check_buffer_tree_ref(eb);
+
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++) {
+		struct page *p = eb->pages[i];
+
+		if (p != accessed)
+			mark_page_accessed(p);
+	}
+}
+
+struct extent_buffer *find_extent_buffer(struct btrfs_fs_info *fs_info,
+					 u64 start)
+{
+	struct extent_buffer *eb;
+
+	eb = find_extent_buffer_nolock(fs_info, start);
+	if (!eb)
+		return NULL;
+	/*
+	 * Lock our eb's refs_lock to avoid races with free_extent_buffer().
+	 * When we get our eb it might be flagged with EXTENT_BUFFER_STALE and
+	 * another task running free_extent_buffer() might have seen that flag
+	 * set, eb->refs == 2, that the buffer isn't under IO (dirty and
+	 * writeback flags not set) and it's still in the tree (flag
+	 * EXTENT_BUFFER_TREE_REF set), therefore being in the process of
+	 * decrementing the extent buffer's reference count twice.  So here we
+	 * could race and increment the eb's reference count, clear its stale
+	 * flag, mark it as dirty and drop our reference before the other task
+	 * finishes executing free_extent_buffer, which would later result in
+	 * an attempt to free an extent buffer that is dirty.
+	 */
+	if (test_bit(EXTENT_BUFFER_STALE, &eb->bflags)) {
+		spin_lock(&eb->refs_lock);
+		spin_unlock(&eb->refs_lock);
+	}
+	mark_extent_buffer_accessed(eb, NULL);
+	return eb;
+}
+
+#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
+struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
+					u64 start)
+{
+	struct extent_buffer *eb, *exists = NULL;
+	int ret;
+
+	eb = find_extent_buffer(fs_info, start);
+	if (eb)
+		return eb;
+	eb = alloc_dummy_extent_buffer(fs_info, start);
+	if (!eb)
+		return ERR_PTR(-ENOMEM);
+	eb->fs_info = fs_info;
+again:
+	ret = radix_tree_preload(GFP_NOFS);
+	if (ret) {
+		exists = ERR_PTR(ret);
+		goto free_eb;
+	}
+	spin_lock(&fs_info->buffer_lock);
+	ret = radix_tree_insert(&fs_info->buffer_radix,
+				start >> fs_info->sectorsize_bits, eb);
+	spin_unlock(&fs_info->buffer_lock);
+	radix_tree_preload_end();
+	if (ret == -EEXIST) {
+		exists = find_extent_buffer(fs_info, start);
+		if (exists)
+			goto free_eb;
+		else
+			goto again;
+	}
+	check_buffer_tree_ref(eb);
+	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
+
+	return eb;
+free_eb:
+	btrfs_release_extent_buffer(eb);
+	return exists;
+}
+#endif
+
+static struct extent_buffer *grab_extent_buffer(
+		struct btrfs_fs_info *fs_info, struct page *page)
+{
+	struct extent_buffer *exists;
+
+	/*
+	 * For subpage case, we completely rely on radix tree to ensure we
+	 * don't try to insert two ebs for the same bytenr.  So here we always
+	 * return NULL and just continue.
+	 */
+	if (fs_info->nodesize < PAGE_SIZE)
+		return NULL;
+
+	/* Page not yet attached to an extent buffer */
+	if (!PagePrivate(page))
+		return NULL;
+
+	/*
+	 * We could have already allocated an eb for this page and attached one
+	 * so lets see if we can get a ref on the existing eb, and if we can we
+	 * know it's good and we can just return that one, else we know we can
+	 * just overwrite page->private.
+	 */
+	exists = (struct extent_buffer *)page->private;
+	if (atomic_inc_not_zero(&exists->refs))
+		return exists;
+
+	WARN_ON(PageDirty(page));
+	detach_page_private(page);
+	return NULL;
+}
+
+static int check_eb_alignment(struct btrfs_fs_info *fs_info, u64 start)
+{
+	if (!IS_ALIGNED(start, fs_info->sectorsize)) {
+		btrfs_err(fs_info, "bad tree block start %llu", start);
+		return -EINVAL;
+	}
+
+	if (fs_info->nodesize < PAGE_SIZE &&
+	    offset_in_page(start) + fs_info->nodesize > PAGE_SIZE) {
+		btrfs_err(fs_info,
+		"tree block crosses page boundary, start %llu nodesize %u",
+			  start, fs_info->nodesize);
+		return -EINVAL;
+	}
+	if (fs_info->nodesize >= PAGE_SIZE &&
+	    !PAGE_ALIGNED(start)) {
+		btrfs_err(fs_info,
+		"tree block is not page aligned, start %llu nodesize %u",
+			  start, fs_info->nodesize);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
+					  u64 start, u64 owner_root, int level)
+{
+	unsigned long len = fs_info->nodesize;
+	int num_pages;
+	int i;
+	unsigned long index = start >> PAGE_SHIFT;
+	struct extent_buffer *eb;
+	struct extent_buffer *exists = NULL;
+	struct page *p;
+	struct address_space *mapping = fs_info->btree_inode->i_mapping;
+	struct btrfs_subpage *prealloc = NULL;
+	u64 lockdep_owner = owner_root;
+	int uptodate = 1;
+	int ret;
+
+	if (check_eb_alignment(fs_info, start))
+		return ERR_PTR(-EINVAL);
+
+#if BITS_PER_LONG == 32
+	if (start >= MAX_LFS_FILESIZE) {
+		btrfs_err_rl(fs_info,
+		"extent buffer %llu is beyond 32bit page cache limit", start);
+		btrfs_err_32bit_limit(fs_info);
+		return ERR_PTR(-EOVERFLOW);
+	}
+	if (start >= BTRFS_32BIT_EARLY_WARN_THRESHOLD)
+		btrfs_warn_32bit_limit(fs_info);
+#endif
+
+	eb = find_extent_buffer(fs_info, start);
+	if (eb)
+		return eb;
+
+	eb = __alloc_extent_buffer(fs_info, start, len);
+	if (!eb)
+		return ERR_PTR(-ENOMEM);
+
+	/*
+	 * The reloc trees are just snapshots, so we need them to appear to be
+	 * just like any other fs tree WRT lockdep.
+	 */
+	if (lockdep_owner == BTRFS_TREE_RELOC_OBJECTID)
+		lockdep_owner = BTRFS_FS_TREE_OBJECTID;
+
+	btrfs_set_buffer_lockdep_class(lockdep_owner, eb, level);
+
+	num_pages = num_extent_pages(eb);
+
+	/*
+	 * Preallocate page->private for subpage case, so that we won't
+	 * allocate memory with private_lock nor page lock hold.
+	 *
+	 * The memory will be freed by attach_extent_buffer_page() or freed
+	 * manually if we exit earlier.
+	 */
+	if (fs_info->nodesize < PAGE_SIZE) {
+		prealloc = btrfs_alloc_subpage(fs_info, BTRFS_SUBPAGE_METADATA);
+		if (IS_ERR(prealloc)) {
+			exists = ERR_CAST(prealloc);
+			goto free_eb;
+		}
+	}
+
+	for (i = 0; i < num_pages; i++, index++) {
+		p = find_or_create_page(mapping, index, GFP_NOFS|__GFP_NOFAIL);
+		if (!p) {
+			exists = ERR_PTR(-ENOMEM);
+			btrfs_free_subpage(prealloc);
+			goto free_eb;
+		}
+
+		spin_lock(&mapping->private_lock);
+		exists = grab_extent_buffer(fs_info, p);
+		if (exists) {
+			spin_unlock(&mapping->private_lock);
+			unlock_page(p);
+			put_page(p);
+			mark_extent_buffer_accessed(exists, p);
+			btrfs_free_subpage(prealloc);
+			goto free_eb;
+		}
+		/* Should not fail, as we have preallocated the memory */
+		ret = attach_extent_buffer_page(eb, p, prealloc);
+		ASSERT(!ret);
+		/*
+		 * To inform we have extra eb under allocation, so that
+		 * detach_extent_buffer_page() won't release the page private
+		 * when the eb hasn't yet been inserted into radix tree.
+		 *
+		 * The ref will be decreased when the eb released the page, in
+		 * detach_extent_buffer_page().
+		 * Thus needs no special handling in error path.
+		 */
+		btrfs_page_inc_eb_refs(fs_info, p);
+		spin_unlock(&mapping->private_lock);
+
+		WARN_ON(btrfs_page_test_dirty(fs_info, p, eb->start, eb->len));
+		eb->pages[i] = p;
+		if (!btrfs_page_test_uptodate(fs_info, p, eb->start, eb->len))
+			uptodate = 0;
+
+		/*
+		 * We can't unlock the pages just yet since the extent buffer
+		 * hasn't been properly inserted in the radix tree, this
+		 * opens a race with btree_release_folio which can free a page
+		 * while we are still filling in all pages for the buffer and
+		 * we could crash.
+		 */
+	}
+	if (uptodate)
+		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
+again:
+	ret = radix_tree_preload(GFP_NOFS);
+	if (ret) {
+		exists = ERR_PTR(ret);
+		goto free_eb;
+	}
+
+	spin_lock(&fs_info->buffer_lock);
+	ret = radix_tree_insert(&fs_info->buffer_radix,
+				start >> fs_info->sectorsize_bits, eb);
+	spin_unlock(&fs_info->buffer_lock);
+	radix_tree_preload_end();
+	if (ret == -EEXIST) {
+		exists = find_extent_buffer(fs_info, start);
+		if (exists)
+			goto free_eb;
+		else
+			goto again;
+	}
+	/* add one reference for the tree */
+	check_buffer_tree_ref(eb);
+	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
+
+	/*
+	 * Now it's safe to unlock the pages because any calls to
+	 * btree_release_folio will correctly detect that a page belongs to a
+	 * live buffer and won't free them prematurely.
+	 */
+	for (i = 0; i < num_pages; i++)
+		unlock_page(eb->pages[i]);
+	return eb;
+
+free_eb:
+	WARN_ON(!atomic_dec_and_test(&eb->refs));
+	for (i = 0; i < num_pages; i++) {
+		if (eb->pages[i])
+			unlock_page(eb->pages[i]);
+	}
+
+	btrfs_release_extent_buffer(eb);
+	return exists;
+}
+
+static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
+{
+	struct extent_buffer *eb =
+			container_of(head, struct extent_buffer, rcu_head);
+
+	__free_extent_buffer(eb);
+}
+
+static int release_extent_buffer(struct extent_buffer *eb)
+	__releases(&eb->refs_lock)
+{
+	lockdep_assert_held(&eb->refs_lock);
+
+	WARN_ON(atomic_read(&eb->refs) == 0);
+	if (atomic_dec_and_test(&eb->refs)) {
+		if (test_and_clear_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags)) {
+			struct btrfs_fs_info *fs_info = eb->fs_info;
+
+			spin_unlock(&eb->refs_lock);
+
+			spin_lock(&fs_info->buffer_lock);
+			radix_tree_delete(&fs_info->buffer_radix,
+					  eb->start >> fs_info->sectorsize_bits);
+			spin_unlock(&fs_info->buffer_lock);
+		} else {
+			spin_unlock(&eb->refs_lock);
+		}
+
+		btrfs_leak_debug_del_eb(eb);
+		/* Should be safe to release our pages at this point */
+		btrfs_release_extent_buffer_pages(eb);
+#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
+		if (unlikely(test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags))) {
+			__free_extent_buffer(eb);
+			return 1;
+		}
+#endif
+		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
+		return 1;
+	}
+	spin_unlock(&eb->refs_lock);
+
+	return 0;
+}
+
+void free_extent_buffer(struct extent_buffer *eb)
+{
+	int refs;
+	if (!eb)
+		return;
+
+	refs = atomic_read(&eb->refs);
+	while (1) {
+		if ((!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) && refs <= 3)
+		    || (test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) &&
+			refs == 1))
+			break;
+		if (atomic_try_cmpxchg(&eb->refs, &refs, refs - 1))
+			return;
+	}
+
+	spin_lock(&eb->refs_lock);
+	if (atomic_read(&eb->refs) == 2 &&
+	    test_bit(EXTENT_BUFFER_STALE, &eb->bflags) &&
+	    !extent_buffer_under_io(eb) &&
+	    test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
+		atomic_dec(&eb->refs);
+
+	/*
+	 * I know this is terrible, but it's temporary until we stop tracking
+	 * the uptodate bits and such for the extent buffers.
+	 */
+	release_extent_buffer(eb);
+}
+
+void free_extent_buffer_stale(struct extent_buffer *eb)
+{
+	if (!eb)
+		return;
+
+	spin_lock(&eb->refs_lock);
+	set_bit(EXTENT_BUFFER_STALE, &eb->bflags);
+
+	if (atomic_read(&eb->refs) == 2 && !extent_buffer_under_io(eb) &&
+	    test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
+		atomic_dec(&eb->refs);
+	release_extent_buffer(eb);
+}
+
+static void btree_clear_page_dirty(struct page *page)
+{
+	ASSERT(PageDirty(page));
+	ASSERT(PageLocked(page));
+	clear_page_dirty_for_io(page);
+	xa_lock_irq(&page->mapping->i_pages);
+	if (!PageDirty(page))
+		__xa_clear_mark(&page->mapping->i_pages,
+				page_index(page), PAGECACHE_TAG_DIRTY);
+	xa_unlock_irq(&page->mapping->i_pages);
+}
+
+static void clear_subpage_extent_buffer_dirty(const struct extent_buffer *eb)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	struct page *page = eb->pages[0];
+	bool last;
+
+	/* btree_clear_page_dirty() needs page locked */
+	lock_page(page);
+	last = btrfs_subpage_clear_and_test_dirty(fs_info, page, eb->start,
+						  eb->len);
+	if (last)
+		btree_clear_page_dirty(page);
+	unlock_page(page);
+	WARN_ON(atomic_read(&eb->refs) == 0);
+}
+
+void btrfs_clear_buffer_dirty(struct btrfs_trans_handle *trans,
+			      struct extent_buffer *eb)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	int i;
+	int num_pages;
+	struct page *page;
+
+	btrfs_assert_tree_write_locked(eb);
+
+	if (trans && btrfs_header_generation(eb) != trans->transid)
+		return;
+
+	if (!test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags))
+		return;
+
+	percpu_counter_add_batch(&fs_info->dirty_metadata_bytes, -eb->len,
+				 fs_info->dirty_metadata_batch);
+
+	if (eb->fs_info->nodesize < PAGE_SIZE)
+		return clear_subpage_extent_buffer_dirty(eb);
+
+	num_pages = num_extent_pages(eb);
+
+	for (i = 0; i < num_pages; i++) {
+		page = eb->pages[i];
+		if (!PageDirty(page))
+			continue;
+		lock_page(page);
+		btree_clear_page_dirty(page);
+		unlock_page(page);
+	}
+	WARN_ON(atomic_read(&eb->refs) == 0);
+}
+
+void set_extent_buffer_dirty(struct extent_buffer *eb)
+{
+	int i;
+	int num_pages;
+	bool was_dirty;
+
+	check_buffer_tree_ref(eb);
+
+	was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);
+
+	num_pages = num_extent_pages(eb);
+	WARN_ON(atomic_read(&eb->refs) == 0);
+	WARN_ON(!test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags));
+
+	if (!was_dirty) {
+		bool subpage = eb->fs_info->nodesize < PAGE_SIZE;
+
+		/*
+		 * For subpage case, we can have other extent buffers in the
+		 * same page, and in clear_subpage_extent_buffer_dirty() we
+		 * have to clear page dirty without subpage lock held.
+		 * This can cause race where our page gets dirty cleared after
+		 * we just set it.
+		 *
+		 * Thankfully, clear_subpage_extent_buffer_dirty() has locked
+		 * its page for other reasons, we can use page lock to prevent
+		 * the above race.
+		 */
+		if (subpage)
+			lock_page(eb->pages[0]);
+		for (i = 0; i < num_pages; i++)
+			btrfs_page_set_dirty(eb->fs_info, eb->pages[i],
+					     eb->start, eb->len);
+		if (subpage)
+			unlock_page(eb->pages[0]);
+		percpu_counter_add_batch(&eb->fs_info->dirty_metadata_bytes,
+					 eb->len,
+					 eb->fs_info->dirty_metadata_batch);
+	}
+#ifdef CONFIG_BTRFS_DEBUG
+	for (i = 0; i < num_pages; i++)
+		ASSERT(PageDirty(eb->pages[i]));
+#endif
+}
+
+void clear_extent_buffer_uptodate(struct extent_buffer *eb)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	struct page *page;
+	int num_pages;
+	int i;
+
+	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++) {
+		page = eb->pages[i];
+		if (!page)
+			continue;
+
+		/*
+		 * This is special handling for metadata subpage, as regular
+		 * btrfs_is_subpage() can not handle cloned/dummy metadata.
+		 */
+		if (fs_info->nodesize >= PAGE_SIZE)
+			ClearPageUptodate(page);
+		else
+			btrfs_subpage_clear_uptodate(fs_info, page, eb->start,
+						     eb->len);
+	}
+}
+
+void set_extent_buffer_uptodate(struct extent_buffer *eb)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	struct page *page;
+	int num_pages;
+	int i;
+
+	set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++) {
+		page = eb->pages[i];
+
+		/*
+		 * This is special handling for metadata subpage, as regular
+		 * btrfs_is_subpage() can not handle cloned/dummy metadata.
+		 */
+		if (fs_info->nodesize >= PAGE_SIZE)
+			SetPageUptodate(page);
+		else
+			btrfs_subpage_set_uptodate(fs_info, page, eb->start,
+						   eb->len);
+	}
+}
+
+static void extent_buffer_read_end_io(struct btrfs_bio *bbio)
+{
+	struct extent_buffer *eb = bbio->private;
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+	bool uptodate = !bbio->bio.bi_status;
+	struct bvec_iter_all iter_all;
+	struct bio_vec *bvec;
+	u32 bio_offset = 0;
+
+	eb->read_mirror = bbio->mirror_num;
+
+	if (uptodate &&
+	    btrfs_validate_extent_buffer(eb, &bbio->parent_check) < 0)
+		uptodate = false;
+
+	if (uptodate) {
+		set_extent_buffer_uptodate(eb);
+	} else {
+		clear_extent_buffer_uptodate(eb);
+		set_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
+	}
+
+	bio_for_each_segment_all(bvec, &bbio->bio, iter_all) {
+		u64 start = eb->start + bio_offset;
+		struct page *page = bvec->bv_page;
+		u32 len = bvec->bv_len;
+
+		if (uptodate)
+			btrfs_page_set_uptodate(fs_info, page, start, len);
+		else
+			btrfs_page_clear_uptodate(fs_info, page, start, len);
+
+		bio_offset += len;
+	}
+
+	clear_bit(EXTENT_BUFFER_READING, &eb->bflags);
+	smp_mb__after_atomic();
+	wake_up_bit(&eb->bflags, EXTENT_BUFFER_READING);
+	free_extent_buffer(eb);
+
+	bio_put(&bbio->bio);
+}
+
+int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
+			     struct btrfs_tree_parent_check *check)
+{
+	int num_pages = num_extent_pages(eb), i;
+	struct btrfs_bio *bbio;
+
+	if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
+		return 0;
+
+	/*
+	 * We could have had EXTENT_BUFFER_UPTODATE cleared by the write
+	 * operation, which could potentially still be in flight.  In this case
+	 * we simply want to return an error.
+	 */
+	if (unlikely(test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)))
+		return -EIO;
+
+	/* Someone else is already reading the buffer, just wait for it. */
+	if (test_and_set_bit(EXTENT_BUFFER_READING, &eb->bflags))
+		goto done;
+
+	clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
+	eb->read_mirror = 0;
+	check_buffer_tree_ref(eb);
+	atomic_inc(&eb->refs);
+
+	bbio = btrfs_bio_alloc(INLINE_EXTENT_BUFFER_PAGES,
+			       REQ_OP_READ | REQ_META, eb->fs_info,
+			       extent_buffer_read_end_io, eb);
+	bbio->bio.bi_iter.bi_sector = eb->start >> SECTOR_SHIFT;
+	bbio->inode = BTRFS_I(eb->fs_info->btree_inode);
+	bbio->file_offset = eb->start;
+	memcpy(&bbio->parent_check, check, sizeof(*check));
+	if (eb->fs_info->nodesize < PAGE_SIZE) {
+		__bio_add_page(&bbio->bio, eb->pages[0], eb->len,
+			       eb->start - page_offset(eb->pages[0]));
+	} else {
+		for (i = 0; i < num_pages; i++)
+			__bio_add_page(&bbio->bio, eb->pages[i], PAGE_SIZE, 0);
+	}
+	btrfs_submit_bio(bbio, mirror_num);
+
+done:
+	if (wait == WAIT_COMPLETE) {
+		wait_on_bit_io(&eb->bflags, EXTENT_BUFFER_READING, TASK_UNINTERRUPTIBLE);
+		if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
+			return -EIO;
+	}
+
+	return 0;
+}
+
+static bool report_eb_range(const struct extent_buffer *eb, unsigned long start,
+			    unsigned long len)
+{
+	btrfs_warn(eb->fs_info,
+		"access to eb bytenr %llu len %lu out of range start %lu len %lu",
+		eb->start, eb->len, start, len);
+	WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
+
+	return true;
+}
+
+/*
+ * Check if the [start, start + len) range is valid before reading/writing
+ * the eb.
+ * NOTE: @start and @len are offset inside the eb, not logical address.
+ *
+ * Caller should not touch the dst/src memory if this function returns error.
+ */
+static inline int check_eb_range(const struct extent_buffer *eb,
+				 unsigned long start, unsigned long len)
+{
+	unsigned long offset;
+
+	/* start, start + len should not go beyond eb->len nor overflow */
+	if (unlikely(check_add_overflow(start, len, &offset) || offset > eb->len))
+		return report_eb_range(eb, start, len);
+
+	return false;
+}
+
+void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
+			unsigned long start, unsigned long len)
+{
+	size_t cur;
+	size_t offset;
+	struct page *page;
+	char *kaddr;
+	char *dst = (char *)dstv;
+	unsigned long i = get_eb_page_index(start);
+
+	if (check_eb_range(eb, start, len)) {
+		/*
+		 * Invalid range hit, reset the memory, so callers won't get
+		 * some random garbage for their uninitialzed memory.
+		 */
+		memset(dstv, 0, len);
+		return;
+	}
+
+	offset = get_eb_offset_in_page(eb, start);
+
+	while (len > 0) {
+		page = eb->pages[i];
+
+		cur = min(len, (PAGE_SIZE - offset));
+		kaddr = page_address(page);
+		memcpy(dst, kaddr + offset, cur);
+
+		dst += cur;
+		len -= cur;
+		offset = 0;
+		i++;
+	}
+}
+
+int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb,
+				       void __user *dstv,
+				       unsigned long start, unsigned long len)
+{
+	size_t cur;
+	size_t offset;
+	struct page *page;
+	char *kaddr;
+	char __user *dst = (char __user *)dstv;
+	unsigned long i = get_eb_page_index(start);
+	int ret = 0;
+
+	WARN_ON(start > eb->len);
+	WARN_ON(start + len > eb->start + eb->len);
+
+	offset = get_eb_offset_in_page(eb, start);
+
+	while (len > 0) {
+		page = eb->pages[i];
+
+		cur = min(len, (PAGE_SIZE - offset));
+		kaddr = page_address(page);
+		if (copy_to_user_nofault(dst, kaddr + offset, cur)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		dst += cur;
+		len -= cur;
+		offset = 0;
+		i++;
+	}
+
+	return ret;
+}
+
+int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
+			 unsigned long start, unsigned long len)
+{
+	size_t cur;
+	size_t offset;
+	struct page *page;
+	char *kaddr;
+	char *ptr = (char *)ptrv;
+	unsigned long i = get_eb_page_index(start);
+	int ret = 0;
+
+	if (check_eb_range(eb, start, len))
+		return -EINVAL;
+
+	offset = get_eb_offset_in_page(eb, start);
+
+	while (len > 0) {
+		page = eb->pages[i];
+
+		cur = min(len, (PAGE_SIZE - offset));
+
+		kaddr = page_address(page);
+		ret = memcmp(ptr, kaddr + offset, cur);
+		if (ret)
+			break;
+
+		ptr += cur;
+		len -= cur;
+		offset = 0;
+		i++;
+	}
+	return ret;
+}
+
+/*
+ * Check that the extent buffer is uptodate.
+ *
+ * For regular sector size == PAGE_SIZE case, check if @page is uptodate.
+ * For subpage case, check if the range covered by the eb has EXTENT_UPTODATE.
+ */
+static void assert_eb_page_uptodate(const struct extent_buffer *eb,
+				    struct page *page)
+{
+	struct btrfs_fs_info *fs_info = eb->fs_info;
+
+	/*
+	 * If we are using the commit root we could potentially clear a page
+	 * Uptodate while we're using the extent buffer that we've previously
+	 * looked up.  We don't want to complain in this case, as the page was
+	 * valid before, we just didn't write it out.  Instead we want to catch
+	 * the case where we didn't actually read the block properly, which
+	 * would have !PageUptodate and !EXTENT_BUFFER_WRITE_ERR.
+	 */
+	if (test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))
+		return;
+
+	if (fs_info->nodesize < PAGE_SIZE) {
+		if (WARN_ON(!btrfs_subpage_test_uptodate(fs_info, page,
+							 eb->start, eb->len)))
+			btrfs_subpage_dump_bitmap(fs_info, page, eb->start, eb->len);
+	} else {
+		WARN_ON(!PageUptodate(page));
+	}
+}
+
+static void __write_extent_buffer(const struct extent_buffer *eb,
+				  const void *srcv, unsigned long start,
+				  unsigned long len, bool use_memmove)
+{
+	size_t cur;
+	size_t offset;
+	struct page *page;
+	char *kaddr;
+	char *src = (char *)srcv;
+	unsigned long i = get_eb_page_index(start);
+	/* For unmapped (dummy) ebs, no need to check their uptodate status. */
+	const bool check_uptodate = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
+
+	WARN_ON(test_bit(EXTENT_BUFFER_NO_CHECK, &eb->bflags));
+
+	if (check_eb_range(eb, start, len))
+		return;
+
+	offset = get_eb_offset_in_page(eb, start);
+
+	while (len > 0) {
+		page = eb->pages[i];
+		if (check_uptodate)
+			assert_eb_page_uptodate(eb, page);
+
+		cur = min(len, PAGE_SIZE - offset);
+		kaddr = page_address(page);
+		if (use_memmove)
+			memmove(kaddr + offset, src, cur);
+		else
+			memcpy(kaddr + offset, src, cur);
+
+		src += cur;
+		len -= cur;
+		offset = 0;
+		i++;
+	}
+}
+
+void write_extent_buffer(const struct extent_buffer *eb, const void *srcv,
+			 unsigned long start, unsigned long len)
+{
+	return __write_extent_buffer(eb, srcv, start, len, false);
+}
+
+static void memset_extent_buffer(const struct extent_buffer *eb, int c,
+				 unsigned long start, unsigned long len)
+{
+	unsigned long cur = start;
+
+	while (cur < start + len) {
+		unsigned long index = get_eb_page_index(cur);
+		unsigned int offset = get_eb_offset_in_page(eb, cur);
+		unsigned int cur_len = min(start + len - cur, PAGE_SIZE - offset);
+		struct page *page = eb->pages[index];
+
+		assert_eb_page_uptodate(eb, page);
+		memset(page_address(page) + offset, c, cur_len);
+
+		cur += cur_len;
+	}
+}
+
+void memzero_extent_buffer(const struct extent_buffer *eb, unsigned long start,
+			   unsigned long len)
+{
+	if (check_eb_range(eb, start, len))
+		return;
+	return memset_extent_buffer(eb, 0, start, len);
+}
+
+void copy_extent_buffer_full(const struct extent_buffer *dst,
+			     const struct extent_buffer *src)
+{
+	unsigned long cur = 0;
+
+	ASSERT(dst->len == src->len);
+
+	while (cur < src->len) {
+		unsigned long index = get_eb_page_index(cur);
+		unsigned long offset = get_eb_offset_in_page(src, cur);
+		unsigned long cur_len = min(src->len, PAGE_SIZE - offset);
+		void *addr = page_address(src->pages[index]) + offset;
+
+		write_extent_buffer(dst, addr, cur, cur_len);
+
+		cur += cur_len;
+	}
+}
+
+void copy_extent_buffer(const struct extent_buffer *dst,
+			const struct extent_buffer *src,
+			unsigned long dst_offset, unsigned long src_offset,
+			unsigned long len)
+{
+	u64 dst_len = dst->len;
+	size_t cur;
+	size_t offset;
+	struct page *page;
+	char *kaddr;
+	unsigned long i = get_eb_page_index(dst_offset);
+
+	if (check_eb_range(dst, dst_offset, len) ||
+	    check_eb_range(src, src_offset, len))
+		return;
+
+	WARN_ON(src->len != dst_len);
+
+	offset = get_eb_offset_in_page(dst, dst_offset);
+
+	while (len > 0) {
+		page = dst->pages[i];
+		assert_eb_page_uptodate(dst, page);
+
+		cur = min(len, (unsigned long)(PAGE_SIZE - offset));
+
+		kaddr = page_address(page);
+		read_extent_buffer(src, kaddr + offset, src_offset, cur);
+
+		src_offset += cur;
+		len -= cur;
+		offset = 0;
+		i++;
+	}
+}
+
+/*
+ * eb_bitmap_offset() - calculate the page and offset of the byte containing the
+ * given bit number
+ * @eb: the extent buffer
+ * @start: offset of the bitmap item in the extent buffer
+ * @nr: bit number
+ * @page_index: return index of the page in the extent buffer that contains the
+ * given bit number
+ * @page_offset: return offset into the page given by page_index
+ *
+ * This helper hides the ugliness of finding the byte in an extent buffer which
+ * contains a given bit.
+ */
+static inline void eb_bitmap_offset(const struct extent_buffer *eb,
+				    unsigned long start, unsigned long nr,
+				    unsigned long *page_index,
+				    size_t *page_offset)
+{
+	size_t byte_offset = BIT_BYTE(nr);
+	size_t offset;
+
+	/*
+	 * The byte we want is the offset of the extent buffer + the offset of
+	 * the bitmap item in the extent buffer + the offset of the byte in the
+	 * bitmap item.
+	 */
+	offset = start + offset_in_page(eb->start) + byte_offset;
+
+	*page_index = offset >> PAGE_SHIFT;
+	*page_offset = offset_in_page(offset);
+}
+
+/*
+ * Determine whether a bit in a bitmap item is set.
+ *
+ * @eb:     the extent buffer
+ * @start:  offset of the bitmap item in the extent buffer
+ * @nr:     bit number to test
+ */
+int extent_buffer_test_bit(const struct extent_buffer *eb, unsigned long start,
+			   unsigned long nr)
+{
+	u8 *kaddr;
+	struct page *page;
+	unsigned long i;
+	size_t offset;
+
+	eb_bitmap_offset(eb, start, nr, &i, &offset);
+	page = eb->pages[i];
+	assert_eb_page_uptodate(eb, page);
+	kaddr = page_address(page);
+	return 1U & (kaddr[offset] >> (nr & (BITS_PER_BYTE - 1)));
+}
+
+static u8 *extent_buffer_get_byte(const struct extent_buffer *eb, unsigned long bytenr)
+{
+	unsigned long index = get_eb_page_index(bytenr);
+
+	if (check_eb_range(eb, bytenr, 1))
+		return NULL;
+	return page_address(eb->pages[index]) + get_eb_offset_in_page(eb, bytenr);
+}
+
+/*
+ * Set an area of a bitmap to 1.
+ *
+ * @eb:     the extent buffer
+ * @start:  offset of the bitmap item in the extent buffer
+ * @pos:    bit number of the first bit
+ * @len:    number of bits to set
+ */
+void extent_buffer_bitmap_set(const struct extent_buffer *eb, unsigned long start,
+			      unsigned long pos, unsigned long len)
+{
+	unsigned int first_byte = start + BIT_BYTE(pos);
+	unsigned int last_byte = start + BIT_BYTE(pos + len - 1);
+	const bool same_byte = (first_byte == last_byte);
+	u8 mask = BITMAP_FIRST_BYTE_MASK(pos);
+	u8 *kaddr;
+
+	if (same_byte)
+		mask &= BITMAP_LAST_BYTE_MASK(pos + len);
+
+	/* Handle the first byte. */
+	kaddr = extent_buffer_get_byte(eb, first_byte);
+	*kaddr |= mask;
+	if (same_byte)
+		return;
+
+	/* Handle the byte aligned part. */
+	ASSERT(first_byte + 1 <= last_byte);
+	memset_extent_buffer(eb, 0xff, first_byte + 1, last_byte - first_byte - 1);
+
+	/* Handle the last byte. */
+	kaddr = extent_buffer_get_byte(eb, last_byte);
+	*kaddr |= BITMAP_LAST_BYTE_MASK(pos + len);
+}
+
+
+/*
+ * Clear an area of a bitmap.
+ *
+ * @eb:     the extent buffer
+ * @start:  offset of the bitmap item in the extent buffer
+ * @pos:    bit number of the first bit
+ * @len:    number of bits to clear
+ */
+void extent_buffer_bitmap_clear(const struct extent_buffer *eb,
+				unsigned long start, unsigned long pos,
+				unsigned long len)
+{
+	unsigned int first_byte = start + BIT_BYTE(pos);
+	unsigned int last_byte = start + BIT_BYTE(pos + len - 1);
+	const bool same_byte = (first_byte == last_byte);
+	u8 mask = BITMAP_FIRST_BYTE_MASK(pos);
+	u8 *kaddr;
+
+	if (same_byte)
+		mask &= BITMAP_LAST_BYTE_MASK(pos + len);
+
+	/* Handle the first byte. */
+	kaddr = extent_buffer_get_byte(eb, first_byte);
+	*kaddr &= ~mask;
+	if (same_byte)
+		return;
+
+	/* Handle the byte aligned part. */
+	ASSERT(first_byte + 1 <= last_byte);
+	memset_extent_buffer(eb, 0, first_byte + 1, last_byte - first_byte - 1);
+
+	/* Handle the last byte. */
+	kaddr = extent_buffer_get_byte(eb, last_byte);
+	*kaddr &= ~BITMAP_LAST_BYTE_MASK(pos + len);
+}
+
+static inline bool areas_overlap(unsigned long src, unsigned long dst, unsigned long len)
+{
+	unsigned long distance = (src > dst) ? src - dst : dst - src;
+	return distance < len;
+}
+
+void memcpy_extent_buffer(const struct extent_buffer *dst,
+			  unsigned long dst_offset, unsigned long src_offset,
+			  unsigned long len)
+{
+	unsigned long cur_off = 0;
+
+	if (check_eb_range(dst, dst_offset, len) ||
+	    check_eb_range(dst, src_offset, len))
+		return;
+
+	while (cur_off < len) {
+		unsigned long cur_src = cur_off + src_offset;
+		unsigned long pg_index = get_eb_page_index(cur_src);
+		unsigned long pg_off = get_eb_offset_in_page(dst, cur_src);
+		unsigned long cur_len = min(src_offset + len - cur_src,
+					    PAGE_SIZE - pg_off);
+		void *src_addr = page_address(dst->pages[pg_index]) + pg_off;
+		const bool use_memmove = areas_overlap(src_offset + cur_off,
+						       dst_offset + cur_off, cur_len);
+
+		__write_extent_buffer(dst, src_addr, dst_offset + cur_off, cur_len,
+				      use_memmove);
+		cur_off += cur_len;
+	}
+}
+
+void memmove_extent_buffer(const struct extent_buffer *dst,
+			   unsigned long dst_offset, unsigned long src_offset,
+			   unsigned long len)
+{
+	unsigned long dst_end = dst_offset + len - 1;
+	unsigned long src_end = src_offset + len - 1;
+
+	if (check_eb_range(dst, dst_offset, len) ||
+	    check_eb_range(dst, src_offset, len))
+		return;
+
+	if (dst_offset < src_offset) {
+		memcpy_extent_buffer(dst, dst_offset, src_offset, len);
+		return;
+	}
+
+	while (len > 0) {
+		unsigned long src_i;
+		size_t cur;
+		size_t dst_off_in_page;
+		size_t src_off_in_page;
+		void *src_addr;
+		bool use_memmove;
+
+		src_i = get_eb_page_index(src_end);
+
+		dst_off_in_page = get_eb_offset_in_page(dst, dst_end);
+		src_off_in_page = get_eb_offset_in_page(dst, src_end);
+
+		cur = min_t(unsigned long, len, src_off_in_page + 1);
+		cur = min(cur, dst_off_in_page + 1);
+
+		src_addr = page_address(dst->pages[src_i]) + src_off_in_page -
+					cur + 1;
+		use_memmove = areas_overlap(src_end - cur + 1, dst_end - cur + 1,
+					    cur);
+
+		__write_extent_buffer(dst, src_addr, dst_end - cur + 1, cur,
+				      use_memmove);
+
+		dst_end -= cur;
+		src_end -= cur;
+		len -= cur;
+	}
+}
+
+#define GANG_LOOKUP_SIZE	16
+static struct extent_buffer *get_next_extent_buffer(
+		struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
+{
+	struct extent_buffer *gang[GANG_LOOKUP_SIZE];
+	struct extent_buffer *found = NULL;
+	u64 page_start = page_offset(page);
+	u64 cur = page_start;
+
+	ASSERT(in_range(bytenr, page_start, PAGE_SIZE));
+	lockdep_assert_held(&fs_info->buffer_lock);
+
+	while (cur < page_start + PAGE_SIZE) {
+		int ret;
+		int i;
+
+		ret = radix_tree_gang_lookup(&fs_info->buffer_radix,
+				(void **)gang, cur >> fs_info->sectorsize_bits,
+				min_t(unsigned int, GANG_LOOKUP_SIZE,
+				      PAGE_SIZE / fs_info->nodesize));
+		if (ret == 0)
+			goto out;
+		for (i = 0; i < ret; i++) {
+			/* Already beyond page end */
+			if (gang[i]->start >= page_start + PAGE_SIZE)
+				goto out;
+			/* Found one */
+			if (gang[i]->start >= bytenr) {
+				found = gang[i];
+				goto out;
+			}
+		}
+		cur = gang[ret - 1]->start + gang[ret - 1]->len;
+	}
+out:
+	return found;
+}
+
+static int try_release_subpage_extent_buffer(struct page *page)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+	u64 cur = page_offset(page);
+	const u64 end = page_offset(page) + PAGE_SIZE;
+	int ret;
+
+	while (cur < end) {
+		struct extent_buffer *eb = NULL;
+
+		/*
+		 * Unlike try_release_extent_buffer() which uses page->private
+		 * to grab buffer, for subpage case we rely on radix tree, thus
+		 * we need to ensure radix tree consistency.
+		 *
+		 * We also want an atomic snapshot of the radix tree, thus go
+		 * with spinlock rather than RCU.
+		 */
+		spin_lock(&fs_info->buffer_lock);
+		eb = get_next_extent_buffer(fs_info, page, cur);
+		if (!eb) {
+			/* No more eb in the page range after or at cur */
+			spin_unlock(&fs_info->buffer_lock);
+			break;
+		}
+		cur = eb->start + eb->len;
+
+		/*
+		 * The same as try_release_extent_buffer(), to ensure the eb
+		 * won't disappear out from under us.
+		 */
+		spin_lock(&eb->refs_lock);
+		if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
+			spin_unlock(&eb->refs_lock);
+			spin_unlock(&fs_info->buffer_lock);
+			break;
+		}
+		spin_unlock(&fs_info->buffer_lock);
+
+		/*
+		 * If tree ref isn't set then we know the ref on this eb is a
+		 * real ref, so just return, this eb will likely be freed soon
+		 * anyway.
+		 */
+		if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
+			spin_unlock(&eb->refs_lock);
+			break;
+		}
+
+		/*
+		 * Here we don't care about the return value, we will always
+		 * check the page private at the end.  And
+		 * release_extent_buffer() will release the refs_lock.
+		 */
+		release_extent_buffer(eb);
+	}
+	/*
+	 * Finally to check if we have cleared page private, as if we have
+	 * released all ebs in the page, the page private should be cleared now.
+	 */
+	spin_lock(&page->mapping->private_lock);
+	if (!PagePrivate(page))
+		ret = 1;
+	else
+		ret = 0;
+	spin_unlock(&page->mapping->private_lock);
+	return ret;
+
+}
+
+int try_release_extent_buffer(struct page *page)
+{
+	struct extent_buffer *eb;
+
+	if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
+		return try_release_subpage_extent_buffer(page);
+
+	/*
+	 * We need to make sure nobody is changing page->private, as we rely on
+	 * page->private as the pointer to extent buffer.
+	 */
+	spin_lock(&page->mapping->private_lock);
+	if (!PagePrivate(page)) {
+		spin_unlock(&page->mapping->private_lock);
+		return 1;
+	}
+
+	eb = (struct extent_buffer *)page->private;
+	BUG_ON(!eb);
+
+	/*
+	 * This is a little awful but should be ok, we need to make sure that
+	 * the eb doesn't disappear out from under us while we're looking at
+	 * this page.
+	 */
+	spin_lock(&eb->refs_lock);
+	if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
+		spin_unlock(&eb->refs_lock);
+		spin_unlock(&page->mapping->private_lock);
+		return 0;
+	}
+	spin_unlock(&page->mapping->private_lock);
+
+	/*
+	 * If tree ref isn't set then we know the ref on this eb is a real ref,
+	 * so just return, this page will likely be freed soon anyway.
+	 */
+	if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
+		spin_unlock(&eb->refs_lock);
+		return 0;
+	}
+
+	return release_extent_buffer(eb);
+}
+
+/*
+ * btrfs_readahead_tree_block - attempt to readahead a child block
+ * @fs_info:	the fs_info
+ * @bytenr:	bytenr to read
+ * @owner_root: objectid of the root that owns this eb
+ * @gen:	generation for the uptodate check, can be 0
+ * @level:	level for the eb
+ *
+ * Attempt to readahead a tree block at @bytenr.  If @gen is 0 then we do a
+ * normal uptodate check of the eb, without checking the generation.  If we have
+ * to read the block we will not block on anything.
+ */
+void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
+				u64 bytenr, u64 owner_root, u64 gen, int level)
+{
+	struct btrfs_tree_parent_check check = {
+		.has_first_key = 0,
+		.level = level,
+		.transid = gen
+	};
+	struct extent_buffer *eb;
+	int ret;
+
+	eb = btrfs_find_create_tree_block(fs_info, bytenr, owner_root, level);
+	if (IS_ERR(eb))
+		return;
+
+	if (btrfs_buffer_uptodate(eb, gen, 1)) {
+		free_extent_buffer(eb);
+		return;
+	}
+
+	ret = read_extent_buffer_pages(eb, WAIT_NONE, 0, &check);
+	if (ret < 0)
+		free_extent_buffer_stale(eb);
+	else
+		free_extent_buffer(eb);
+}
+
+/*
+ * btrfs_readahead_node_child - readahead a node's child block
+ * @node:	parent node we're reading from
+ * @slot:	slot in the parent node for the child we want to read
+ *
+ * A helper for btrfs_readahead_tree_block, we simply read the bytenr pointed at
+ * the slot in the node provided.
+ */
+void btrfs_readahead_node_child(struct extent_buffer *node, int slot)
+{
+	btrfs_readahead_tree_block(node->fs_info,
+				   btrfs_node_blockptr(node, slot),
+				   btrfs_header_owner(node),
+				   btrfs_node_ptr_generation(node, slot),
+				   btrfs_header_level(node) - 1);
+}