Adding upstream version 4.19.249.upstream/4.19.249

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

1 files changed, 2168 insertions, 0 deletions

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
new file mode 100644
index 000000000..b33a9cd4f
--- /dev/null
+++ b/fs/xfs/xfs_buf.c
@@ -0,0 +1,2168 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2000-2006 Silicon Graphics, Inc.
+ * All Rights Reserved.
+ */
+#include "xfs.h"
+#include <linux/stddef.h>
+#include <linux/errno.h>
+#include <linux/gfp.h>
+#include <linux/pagemap.h>
+#include <linux/init.h>
+#include <linux/vmalloc.h>
+#include <linux/bio.h>
+#include <linux/sysctl.h>
+#include <linux/proc_fs.h>
+#include <linux/workqueue.h>
+#include <linux/percpu.h>
+#include <linux/blkdev.h>
+#include <linux/hash.h>
+#include <linux/kthread.h>
+#include <linux/migrate.h>
+#include <linux/backing-dev.h>
+#include <linux/freezer.h>
+
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_sb.h"
+#include "xfs_mount.h"
+#include "xfs_trace.h"
+#include "xfs_log.h"
+#include "xfs_errortag.h"
+#include "xfs_error.h"
+
+static kmem_zone_t *xfs_buf_zone;
+
+#define xb_to_gfp(flags) \
+	((((flags) & XBF_READ_AHEAD) ? __GFP_NORETRY : GFP_NOFS) | __GFP_NOWARN)
+
+/*
+ * Locking orders
+ *
+ * xfs_buf_ioacct_inc:
+ * xfs_buf_ioacct_dec:
+ *	b_sema (caller holds)
+ *	  b_lock
+ *
+ * xfs_buf_stale:
+ *	b_sema (caller holds)
+ *	  b_lock
+ *	    lru_lock
+ *
+ * xfs_buf_rele:
+ *	b_lock
+ *	  pag_buf_lock
+ *	    lru_lock
+ *
+ * xfs_buftarg_wait_rele
+ *	lru_lock
+ *	  b_lock (trylock due to inversion)
+ *
+ * xfs_buftarg_isolate
+ *	lru_lock
+ *	  b_lock (trylock due to inversion)
+ */
+
+static inline int
+xfs_buf_is_vmapped(
+	struct xfs_buf	*bp)
+{
+	/*
+	 * Return true if the buffer is vmapped.
+	 *
+	 * b_addr is null if the buffer is not mapped, but the code is clever
+	 * enough to know it doesn't have to map a single page, so the check has
+	 * to be both for b_addr and bp->b_page_count > 1.
+	 */
+	return bp->b_addr && bp->b_page_count > 1;
+}
+
+static inline int
+xfs_buf_vmap_len(
+	struct xfs_buf	*bp)
+{
+	return (bp->b_page_count * PAGE_SIZE) - bp->b_offset;
+}
+
+/*
+ * Bump the I/O in flight count on the buftarg if we haven't yet done so for
+ * this buffer. The count is incremented once per buffer (per hold cycle)
+ * because the corresponding decrement is deferred to buffer release. Buffers
+ * can undergo I/O multiple times in a hold-release cycle and per buffer I/O
+ * tracking adds unnecessary overhead. This is used for sychronization purposes
+ * with unmount (see xfs_wait_buftarg()), so all we really need is a count of
+ * in-flight buffers.
+ *
+ * Buffers that are never released (e.g., superblock, iclog buffers) must set
+ * the XBF_NO_IOACCT flag before I/O submission. Otherwise, the buftarg count
+ * never reaches zero and unmount hangs indefinitely.
+ */
+static inline void
+xfs_buf_ioacct_inc(
+	struct xfs_buf	*bp)
+{
+	if (bp->b_flags & XBF_NO_IOACCT)
+		return;
+
+	ASSERT(bp->b_flags & XBF_ASYNC);
+	spin_lock(&bp->b_lock);
+	if (!(bp->b_state & XFS_BSTATE_IN_FLIGHT)) {
+		bp->b_state |= XFS_BSTATE_IN_FLIGHT;
+		percpu_counter_inc(&bp->b_target->bt_io_count);
+	}
+	spin_unlock(&bp->b_lock);
+}
+
+/*
+ * Clear the in-flight state on a buffer about to be released to the LRU or
+ * freed and unaccount from the buftarg.
+ */
+static inline void
+__xfs_buf_ioacct_dec(
+	struct xfs_buf	*bp)
+{
+	lockdep_assert_held(&bp->b_lock);
+
+	if (bp->b_state & XFS_BSTATE_IN_FLIGHT) {
+		bp->b_state &= ~XFS_BSTATE_IN_FLIGHT;
+		percpu_counter_dec(&bp->b_target->bt_io_count);
+	}
+}
+
+static inline void
+xfs_buf_ioacct_dec(
+	struct xfs_buf	*bp)
+{
+	spin_lock(&bp->b_lock);
+	__xfs_buf_ioacct_dec(bp);
+	spin_unlock(&bp->b_lock);
+}
+
+/*
+ * When we mark a buffer stale, we remove the buffer from the LRU and clear the
+ * b_lru_ref count so that the buffer is freed immediately when the buffer
+ * reference count falls to zero. If the buffer is already on the LRU, we need
+ * to remove the reference that LRU holds on the buffer.
+ *
+ * This prevents build-up of stale buffers on the LRU.
+ */
+void
+xfs_buf_stale(
+	struct xfs_buf	*bp)
+{
+	ASSERT(xfs_buf_islocked(bp));
+
+	bp->b_flags |= XBF_STALE;
+
+	/*
+	 * Clear the delwri status so that a delwri queue walker will not
+	 * flush this buffer to disk now that it is stale. The delwri queue has
+	 * a reference to the buffer, so this is safe to do.
+	 */
+	bp->b_flags &= ~_XBF_DELWRI_Q;
+
+	/*
+	 * Once the buffer is marked stale and unlocked, a subsequent lookup
+	 * could reset b_flags. There is no guarantee that the buffer is
+	 * unaccounted (released to LRU) before that occurs. Drop in-flight
+	 * status now to preserve accounting consistency.
+	 */
+	spin_lock(&bp->b_lock);
+	__xfs_buf_ioacct_dec(bp);
+
+	atomic_set(&bp->b_lru_ref, 0);
+	if (!(bp->b_state & XFS_BSTATE_DISPOSE) &&
+	    (list_lru_del(&bp->b_target->bt_lru, &bp->b_lru)))
+		atomic_dec(&bp->b_hold);
+
+	ASSERT(atomic_read(&bp->b_hold) >= 1);
+	spin_unlock(&bp->b_lock);
+}
+
+static int
+xfs_buf_get_maps(
+	struct xfs_buf		*bp,
+	int			map_count)
+{
+	ASSERT(bp->b_maps == NULL);
+	bp->b_map_count = map_count;
+
+	if (map_count == 1) {
+		bp->b_maps = &bp->__b_map;
+		return 0;
+	}
+
+	bp->b_maps = kmem_zalloc(map_count * sizeof(struct xfs_buf_map),
+				KM_NOFS);
+	if (!bp->b_maps)
+		return -ENOMEM;
+	return 0;
+}
+
+/*
+ *	Frees b_pages if it was allocated.
+ */
+static void
+xfs_buf_free_maps(
+	struct xfs_buf	*bp)
+{
+	if (bp->b_maps != &bp->__b_map) {
+		kmem_free(bp->b_maps);
+		bp->b_maps = NULL;
+	}
+}
+
+struct xfs_buf *
+_xfs_buf_alloc(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags)
+{
+	struct xfs_buf		*bp;
+	int			error;
+	int			i;
+
+	bp = kmem_zone_zalloc(xfs_buf_zone, KM_NOFS);
+	if (unlikely(!bp))
+		return NULL;
+
+	/*
+	 * We don't want certain flags to appear in b_flags unless they are
+	 * specifically set by later operations on the buffer.
+	 */
+	flags &= ~(XBF_UNMAPPED | XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD);
+
+	atomic_set(&bp->b_hold, 1);
+	atomic_set(&bp->b_lru_ref, 1);
+	init_completion(&bp->b_iowait);
+	INIT_LIST_HEAD(&bp->b_lru);
+	INIT_LIST_HEAD(&bp->b_list);
+	INIT_LIST_HEAD(&bp->b_li_list);
+	sema_init(&bp->b_sema, 0); /* held, no waiters */
+	spin_lock_init(&bp->b_lock);
+	bp->b_target = target;
+	bp->b_flags = flags;
+
+	/*
+	 * Set length and io_length to the same value initially.
+	 * I/O routines should use io_length, which will be the same in
+	 * most cases but may be reset (e.g. XFS recovery).
+	 */
+	error = xfs_buf_get_maps(bp, nmaps);
+	if (error)  {
+		kmem_zone_free(xfs_buf_zone, bp);
+		return NULL;
+	}
+
+	bp->b_bn = map[0].bm_bn;
+	bp->b_length = 0;
+	for (i = 0; i < nmaps; i++) {
+		bp->b_maps[i].bm_bn = map[i].bm_bn;
+		bp->b_maps[i].bm_len = map[i].bm_len;
+		bp->b_length += map[i].bm_len;
+	}
+	bp->b_io_length = bp->b_length;
+
+	atomic_set(&bp->b_pin_count, 0);
+	init_waitqueue_head(&bp->b_waiters);
+
+	XFS_STATS_INC(target->bt_mount, xb_create);
+	trace_xfs_buf_init(bp, _RET_IP_);
+
+	return bp;
+}
+
+/*
+ *	Allocate a page array capable of holding a specified number
+ *	of pages, and point the page buf at it.
+ */
+STATIC int
+_xfs_buf_get_pages(
+	xfs_buf_t		*bp,
+	int			page_count)
+{
+	/* Make sure that we have a page list */
+	if (bp->b_pages == NULL) {
+		bp->b_page_count = page_count;
+		if (page_count <= XB_PAGES) {
+			bp->b_pages = bp->b_page_array;
+		} else {
+			bp->b_pages = kmem_alloc(sizeof(struct page *) *
+						 page_count, KM_NOFS);
+			if (bp->b_pages == NULL)
+				return -ENOMEM;
+		}
+		memset(bp->b_pages, 0, sizeof(struct page *) * page_count);
+	}
+	return 0;
+}
+
+/*
+ *	Frees b_pages if it was allocated.
+ */
+STATIC void
+_xfs_buf_free_pages(
+	xfs_buf_t	*bp)
+{
+	if (bp->b_pages != bp->b_page_array) {
+		kmem_free(bp->b_pages);
+		bp->b_pages = NULL;
+	}
+}
+
+/*
+ *	Releases the specified buffer.
+ *
+ * 	The modification state of any associated pages is left unchanged.
+ * 	The buffer must not be on any hash - use xfs_buf_rele instead for
+ * 	hashed and refcounted buffers
+ */
+void
+xfs_buf_free(
+	xfs_buf_t		*bp)
+{
+	trace_xfs_buf_free(bp, _RET_IP_);
+
+	ASSERT(list_empty(&bp->b_lru));
+
+	if (bp->b_flags & _XBF_PAGES) {
+		uint		i;
+
+		if (xfs_buf_is_vmapped(bp))
+			vm_unmap_ram(bp->b_addr - bp->b_offset,
+					bp->b_page_count);
+
+		for (i = 0; i < bp->b_page_count; i++) {
+			struct page	*page = bp->b_pages[i];
+
+			__free_page(page);
+		}
+	} else if (bp->b_flags & _XBF_KMEM)
+		kmem_free(bp->b_addr);
+	_xfs_buf_free_pages(bp);
+	xfs_buf_free_maps(bp);
+	kmem_zone_free(xfs_buf_zone, bp);
+}
+
+/*
+ * Allocates all the pages for buffer in question and builds it's page list.
+ */
+STATIC int
+xfs_buf_allocate_memory(
+	xfs_buf_t		*bp,
+	uint			flags)
+{
+	size_t			size;
+	size_t			nbytes, offset;
+	gfp_t			gfp_mask = xb_to_gfp(flags);
+	unsigned short		page_count, i;
+	xfs_off_t		start, end;
+	int			error;
+
+	/*
+	 * for buffers that are contained within a single page, just allocate
+	 * the memory from the heap - there's no need for the complexity of
+	 * page arrays to keep allocation down to order 0.
+	 */
+	size = BBTOB(bp->b_length);
+	if (size < PAGE_SIZE) {
+		bp->b_addr = kmem_alloc(size, KM_NOFS);
+		if (!bp->b_addr) {
+			/* low memory - use alloc_page loop instead */
+			goto use_alloc_page;
+		}
+
+		if (((unsigned long)(bp->b_addr + size - 1) & PAGE_MASK) !=
+		    ((unsigned long)bp->b_addr & PAGE_MASK)) {
+			/* b_addr spans two pages - use alloc_page instead */
+			kmem_free(bp->b_addr);
+			bp->b_addr = NULL;
+			goto use_alloc_page;
+		}
+		bp->b_offset = offset_in_page(bp->b_addr);
+		bp->b_pages = bp->b_page_array;
+		bp->b_pages[0] = virt_to_page(bp->b_addr);
+		bp->b_page_count = 1;
+		bp->b_flags |= _XBF_KMEM;
+		return 0;
+	}
+
+use_alloc_page:
+	start = BBTOB(bp->b_maps[0].bm_bn) >> PAGE_SHIFT;
+	end = (BBTOB(bp->b_maps[0].bm_bn + bp->b_length) + PAGE_SIZE - 1)
+								>> PAGE_SHIFT;
+	page_count = end - start;
+	error = _xfs_buf_get_pages(bp, page_count);
+	if (unlikely(error))
+		return error;
+
+	offset = bp->b_offset;
+	bp->b_flags |= _XBF_PAGES;
+
+	for (i = 0; i < bp->b_page_count; i++) {
+		struct page	*page;
+		uint		retries = 0;
+retry:
+		page = alloc_page(gfp_mask);
+		if (unlikely(page == NULL)) {
+			if (flags & XBF_READ_AHEAD) {
+				bp->b_page_count = i;
+				error = -ENOMEM;
+				goto out_free_pages;
+			}
+
+			/*
+			 * This could deadlock.
+			 *
+			 * But until all the XFS lowlevel code is revamped to
+			 * handle buffer allocation failures we can't do much.
+			 */
+			if (!(++retries % 100))
+				xfs_err(NULL,
+		"%s(%u) possible memory allocation deadlock in %s (mode:0x%x)",
+					current->comm, current->pid,
+					__func__, gfp_mask);
+
+			XFS_STATS_INC(bp->b_target->bt_mount, xb_page_retries);
+			congestion_wait(BLK_RW_ASYNC, HZ/50);
+			goto retry;
+		}
+
+		XFS_STATS_INC(bp->b_target->bt_mount, xb_page_found);
+
+		nbytes = min_t(size_t, size, PAGE_SIZE - offset);
+		size -= nbytes;
+		bp->b_pages[i] = page;
+		offset = 0;
+	}
+	return 0;
+
+out_free_pages:
+	for (i = 0; i < bp->b_page_count; i++)
+		__free_page(bp->b_pages[i]);
+	bp->b_flags &= ~_XBF_PAGES;
+	return error;
+}
+
+/*
+ *	Map buffer into kernel address-space if necessary.
+ */
+STATIC int
+_xfs_buf_map_pages(
+	xfs_buf_t		*bp,
+	uint			flags)
+{
+	ASSERT(bp->b_flags & _XBF_PAGES);
+	if (bp->b_page_count == 1) {
+		/* A single page buffer is always mappable */
+		bp->b_addr = page_address(bp->b_pages[0]) + bp->b_offset;
+	} else if (flags & XBF_UNMAPPED) {
+		bp->b_addr = NULL;
+	} else {
+		int retried = 0;
+		unsigned nofs_flag;
+
+		/*
+		 * vm_map_ram() will allocate auxillary structures (e.g.
+		 * pagetables) with GFP_KERNEL, yet we are likely to be under
+		 * GFP_NOFS context here. Hence we need to tell memory reclaim
+		 * that we are in such a context via PF_MEMALLOC_NOFS to prevent
+		 * memory reclaim re-entering the filesystem here and
+		 * potentially deadlocking.
+		 */
+		nofs_flag = memalloc_nofs_save();
+		do {
+			bp->b_addr = vm_map_ram(bp->b_pages, bp->b_page_count,
+						-1, PAGE_KERNEL);
+			if (bp->b_addr)
+				break;
+			vm_unmap_aliases();
+		} while (retried++ <= 1);
+		memalloc_nofs_restore(nofs_flag);
+
+		if (!bp->b_addr)
+			return -ENOMEM;
+		bp->b_addr += bp->b_offset;
+	}
+
+	return 0;
+}
+
+/*
+ *	Finding and Reading Buffers
+ */
+static int
+_xfs_buf_obj_cmp(
+	struct rhashtable_compare_arg	*arg,
+	const void			*obj)
+{
+	const struct xfs_buf_map	*map = arg->key;
+	const struct xfs_buf		*bp = obj;
+
+	/*
+	 * The key hashing in the lookup path depends on the key being the
+	 * first element of the compare_arg, make sure to assert this.
+	 */
+	BUILD_BUG_ON(offsetof(struct xfs_buf_map, bm_bn) != 0);
+
+	if (bp->b_bn != map->bm_bn)
+		return 1;
+
+	if (unlikely(bp->b_length != map->bm_len)) {
+		/*
+		 * found a block number match. If the range doesn't
+		 * match, the only way this is allowed is if the buffer
+		 * in the cache is stale and the transaction that made
+		 * it stale has not yet committed. i.e. we are
+		 * reallocating a busy extent. Skip this buffer and
+		 * continue searching for an exact match.
+		 */
+		ASSERT(bp->b_flags & XBF_STALE);
+		return 1;
+	}
+	return 0;
+}
+
+static const struct rhashtable_params xfs_buf_hash_params = {
+	.min_size		= 32,	/* empty AGs have minimal footprint */
+	.nelem_hint		= 16,
+	.key_len		= sizeof(xfs_daddr_t),
+	.key_offset		= offsetof(struct xfs_buf, b_bn),
+	.head_offset		= offsetof(struct xfs_buf, b_rhash_head),
+	.automatic_shrinking	= true,
+	.obj_cmpfn		= _xfs_buf_obj_cmp,
+};
+
+int
+xfs_buf_hash_init(
+	struct xfs_perag	*pag)
+{
+	spin_lock_init(&pag->pag_buf_lock);
+	return rhashtable_init(&pag->pag_buf_hash, &xfs_buf_hash_params);
+}
+
+void
+xfs_buf_hash_destroy(
+	struct xfs_perag	*pag)
+{
+	rhashtable_destroy(&pag->pag_buf_hash);
+}
+
+/*
+ * Look up a buffer in the buffer cache and return it referenced and locked
+ * in @found_bp.
+ *
+ * If @new_bp is supplied and we have a lookup miss, insert @new_bp into the
+ * cache.
+ *
+ * If XBF_TRYLOCK is set in @flags, only try to lock the buffer and return
+ * -EAGAIN if we fail to lock it.
+ *
+ * Return values are:
+ *	-EFSCORRUPTED if have been supplied with an invalid address
+ *	-EAGAIN on trylock failure
+ *	-ENOENT if we fail to find a match and @new_bp was NULL
+ *	0, with @found_bp:
+ *		- @new_bp if we inserted it into the cache
+ *		- the buffer we found and locked.
+ */
+static int
+xfs_buf_find(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		*new_bp,
+	struct xfs_buf		**found_bp)
+{
+	struct xfs_perag	*pag;
+	xfs_buf_t		*bp;
+	struct xfs_buf_map	cmap = { .bm_bn = map[0].bm_bn };
+	xfs_daddr_t		eofs;
+	int			i;
+
+	*found_bp = NULL;
+
+	for (i = 0; i < nmaps; i++)
+		cmap.bm_len += map[i].bm_len;
+
+	/* Check for IOs smaller than the sector size / not sector aligned */
+	ASSERT(!(BBTOB(cmap.bm_len) < btp->bt_meta_sectorsize));
+	ASSERT(!(BBTOB(cmap.bm_bn) & (xfs_off_t)btp->bt_meta_sectormask));
+
+	/*
+	 * Corrupted block numbers can get through to here, unfortunately, so we
+	 * have to check that the buffer falls within the filesystem bounds.
+	 */
+	eofs = XFS_FSB_TO_BB(btp->bt_mount, btp->bt_mount->m_sb.sb_dblocks);
+	if (cmap.bm_bn < 0 || cmap.bm_bn >= eofs) {
+		xfs_alert(btp->bt_mount,
+			  "%s: daddr 0x%llx out of range, EOFS 0x%llx",
+			  __func__, cmap.bm_bn, eofs);
+		WARN_ON(1);
+		return -EFSCORRUPTED;
+	}
+
+	pag = xfs_perag_get(btp->bt_mount,
+			    xfs_daddr_to_agno(btp->bt_mount, cmap.bm_bn));
+
+	spin_lock(&pag->pag_buf_lock);
+	bp = rhashtable_lookup_fast(&pag->pag_buf_hash, &cmap,
+				    xfs_buf_hash_params);
+	if (bp) {
+		atomic_inc(&bp->b_hold);
+		goto found;
+	}
+
+	/* No match found */
+	if (!new_bp) {
+		XFS_STATS_INC(btp->bt_mount, xb_miss_locked);
+		spin_unlock(&pag->pag_buf_lock);
+		xfs_perag_put(pag);
+		return -ENOENT;
+	}
+
+	/* the buffer keeps the perag reference until it is freed */
+	new_bp->b_pag = pag;
+	rhashtable_insert_fast(&pag->pag_buf_hash, &new_bp->b_rhash_head,
+			       xfs_buf_hash_params);
+	spin_unlock(&pag->pag_buf_lock);
+	*found_bp = new_bp;
+	return 0;
+
+found:
+	spin_unlock(&pag->pag_buf_lock);
+	xfs_perag_put(pag);
+
+	if (!xfs_buf_trylock(bp)) {
+		if (flags & XBF_TRYLOCK) {
+			xfs_buf_rele(bp);
+			XFS_STATS_INC(btp->bt_mount, xb_busy_locked);
+			return -EAGAIN;
+		}
+		xfs_buf_lock(bp);
+		XFS_STATS_INC(btp->bt_mount, xb_get_locked_waited);
+	}
+
+	/*
+	 * if the buffer is stale, clear all the external state associated with
+	 * it. We need to keep flags such as how we allocated the buffer memory
+	 * intact here.
+	 */
+	if (bp->b_flags & XBF_STALE) {
+		ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
+		ASSERT(bp->b_iodone == NULL);
+		bp->b_flags &= _XBF_KMEM | _XBF_PAGES;
+		bp->b_ops = NULL;
+	}
+
+	trace_xfs_buf_find(bp, flags, _RET_IP_);
+	XFS_STATS_INC(btp->bt_mount, xb_get_locked);
+	*found_bp = bp;
+	return 0;
+}
+
+struct xfs_buf *
+xfs_buf_incore(
+	struct xfs_buftarg	*target,
+	xfs_daddr_t		blkno,
+	size_t			numblks,
+	xfs_buf_flags_t		flags)
+{
+	struct xfs_buf		*bp;
+	int			error;
+	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
+
+	error = xfs_buf_find(target, &map, 1, flags, NULL, &bp);
+	if (error)
+		return NULL;
+	return bp;
+}
+
+/*
+ * Assembles a buffer covering the specified range. The code is optimised for
+ * cache hits, as metadata intensive workloads will see 3 orders of magnitude
+ * more hits than misses.
+ */
+struct xfs_buf *
+xfs_buf_get_map(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags)
+{
+	struct xfs_buf		*bp;
+	struct xfs_buf		*new_bp;
+	int			error = 0;
+
+	error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp);
+
+	switch (error) {
+	case 0:
+		/* cache hit */
+		goto found;
+	case -EAGAIN:
+		/* cache hit, trylock failure, caller handles failure */
+		ASSERT(flags & XBF_TRYLOCK);
+		return NULL;
+	case -ENOENT:
+		/* cache miss, go for insert */
+		break;
+	case -EFSCORRUPTED:
+	default:
+		/*
+		 * None of the higher layers understand failure types
+		 * yet, so return NULL to signal a fatal lookup error.
+		 */
+		return NULL;
+	}
+
+	new_bp = _xfs_buf_alloc(target, map, nmaps, flags);
+	if (unlikely(!new_bp))
+		return NULL;
+
+	error = xfs_buf_allocate_memory(new_bp, flags);
+	if (error) {
+		xfs_buf_free(new_bp);
+		return NULL;
+	}
+
+	error = xfs_buf_find(target, map, nmaps, flags, new_bp, &bp);
+	if (error) {
+		xfs_buf_free(new_bp);
+		return NULL;
+	}
+
+	if (bp != new_bp)
+		xfs_buf_free(new_bp);
+
+found:
+	if (!bp->b_addr) {
+		error = _xfs_buf_map_pages(bp, flags);
+		if (unlikely(error)) {
+			xfs_warn(target->bt_mount,
+				"%s: failed to map pagesn", __func__);
+			xfs_buf_relse(bp);
+			return NULL;
+		}
+	}
+
+	/*
+	 * Clear b_error if this is a lookup from a caller that doesn't expect
+	 * valid data to be found in the buffer.
+	 */
+	if (!(flags & XBF_READ))
+		xfs_buf_ioerror(bp, 0);
+
+	XFS_STATS_INC(target->bt_mount, xb_get);
+	trace_xfs_buf_get(bp, flags, _RET_IP_);
+	return bp;
+}
+
+STATIC int
+_xfs_buf_read(
+	xfs_buf_t		*bp,
+	xfs_buf_flags_t		flags)
+{
+	ASSERT(!(flags & XBF_WRITE));
+	ASSERT(bp->b_maps[0].bm_bn != XFS_BUF_DADDR_NULL);
+
+	bp->b_flags &= ~(XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD);
+	bp->b_flags |= flags & (XBF_READ | XBF_ASYNC | XBF_READ_AHEAD);
+
+	return xfs_buf_submit(bp);
+}
+
+xfs_buf_t *
+xfs_buf_read_map(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	const struct xfs_buf_ops *ops)
+{
+	struct xfs_buf		*bp;
+
+	flags |= XBF_READ;
+
+	bp = xfs_buf_get_map(target, map, nmaps, flags);
+	if (bp) {
+		trace_xfs_buf_read(bp, flags, _RET_IP_);
+
+		if (!(bp->b_flags & XBF_DONE)) {
+			XFS_STATS_INC(target->bt_mount, xb_get_read);
+			bp->b_ops = ops;
+			_xfs_buf_read(bp, flags);
+		} else if (flags & XBF_ASYNC) {
+			/*
+			 * Read ahead call which is already satisfied,
+			 * drop the buffer
+			 */
+			xfs_buf_relse(bp);
+			return NULL;
+		} else {
+			/* We do not want read in the flags */
+			bp->b_flags &= ~XBF_READ;
+		}
+	}
+
+	return bp;
+}
+
+/*
+ *	If we are not low on memory then do the readahead in a deadlock
+ *	safe manner.
+ */
+void
+xfs_buf_readahead_map(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	const struct xfs_buf_ops *ops)
+{
+	if (bdi_read_congested(target->bt_bdev->bd_bdi))
+		return;
+
+	xfs_buf_read_map(target, map, nmaps,
+		     XBF_TRYLOCK|XBF_ASYNC|XBF_READ_AHEAD, ops);
+}
+
+/*
+ * Read an uncached buffer from disk. Allocates and returns a locked
+ * buffer containing the disk contents or nothing.
+ */
+int
+xfs_buf_read_uncached(
+	struct xfs_buftarg	*target,
+	xfs_daddr_t		daddr,
+	size_t			numblks,
+	int			flags,
+	struct xfs_buf		**bpp,
+	const struct xfs_buf_ops *ops)
+{
+	struct xfs_buf		*bp;
+
+	*bpp = NULL;
+
+	bp = xfs_buf_get_uncached(target, numblks, flags);
+	if (!bp)
+		return -ENOMEM;
+
+	/* set up the buffer for a read IO */
+	ASSERT(bp->b_map_count == 1);
+	bp->b_bn = XFS_BUF_DADDR_NULL;  /* always null for uncached buffers */
+	bp->b_maps[0].bm_bn = daddr;
+	bp->b_flags |= XBF_READ;
+	bp->b_ops = ops;
+
+	xfs_buf_submit(bp);
+	if (bp->b_error) {
+		int	error = bp->b_error;
+		xfs_buf_relse(bp);
+		return error;
+	}
+
+	*bpp = bp;
+	return 0;
+}
+
+/*
+ * Return a buffer allocated as an empty buffer and associated to external
+ * memory via xfs_buf_associate_memory() back to it's empty state.
+ */
+void
+xfs_buf_set_empty(
+	struct xfs_buf		*bp,
+	size_t			numblks)
+{
+	if (bp->b_pages)
+		_xfs_buf_free_pages(bp);
+
+	bp->b_pages = NULL;
+	bp->b_page_count = 0;
+	bp->b_addr = NULL;
+	bp->b_length = numblks;
+	bp->b_io_length = numblks;
+
+	ASSERT(bp->b_map_count == 1);
+	bp->b_bn = XFS_BUF_DADDR_NULL;
+	bp->b_maps[0].bm_bn = XFS_BUF_DADDR_NULL;
+	bp->b_maps[0].bm_len = bp->b_length;
+}
+
+static inline struct page *
+mem_to_page(
+	void			*addr)
+{
+	if ((!is_vmalloc_addr(addr))) {
+		return virt_to_page(addr);
+	} else {
+		return vmalloc_to_page(addr);
+	}
+}
+
+int
+xfs_buf_associate_memory(
+	xfs_buf_t		*bp,
+	void			*mem,
+	size_t			len)
+{
+	int			rval;
+	int			i = 0;
+	unsigned long		pageaddr;
+	unsigned long		offset;
+	size_t			buflen;
+	int			page_count;
+
+	pageaddr = (unsigned long)mem & PAGE_MASK;
+	offset = (unsigned long)mem - pageaddr;
+	buflen = PAGE_ALIGN(len + offset);
+	page_count = buflen >> PAGE_SHIFT;
+
+	/* Free any previous set of page pointers */
+	if (bp->b_pages)
+		_xfs_buf_free_pages(bp);
+
+	bp->b_pages = NULL;
+	bp->b_addr = mem;
+
+	rval = _xfs_buf_get_pages(bp, page_count);
+	if (rval)
+		return rval;
+
+	bp->b_offset = offset;
+
+	for (i = 0; i < bp->b_page_count; i++) {
+		bp->b_pages[i] = mem_to_page((void *)pageaddr);
+		pageaddr += PAGE_SIZE;
+	}
+
+	bp->b_io_length = BTOBB(len);
+	bp->b_length = BTOBB(buflen);
+
+	return 0;
+}
+
+xfs_buf_t *
+xfs_buf_get_uncached(
+	struct xfs_buftarg	*target,
+	size_t			numblks,
+	int			flags)
+{
+	unsigned long		page_count;
+	int			error, i;
+	struct xfs_buf		*bp;
+	DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
+
+	/* flags might contain irrelevant bits, pass only what we care about */
+	bp = _xfs_buf_alloc(target, &map, 1, flags & XBF_NO_IOACCT);
+	if (unlikely(bp == NULL))
+		goto fail;
+
+	page_count = PAGE_ALIGN(numblks << BBSHIFT) >> PAGE_SHIFT;
+	error = _xfs_buf_get_pages(bp, page_count);
+	if (error)
+		goto fail_free_buf;
+
+	for (i = 0; i < page_count; i++) {
+		bp->b_pages[i] = alloc_page(xb_to_gfp(flags));
+		if (!bp->b_pages[i])
+			goto fail_free_mem;
+	}
+	bp->b_flags |= _XBF_PAGES;
+
+	error = _xfs_buf_map_pages(bp, 0);
+	if (unlikely(error)) {
+		xfs_warn(target->bt_mount,
+			"%s: failed to map pages", __func__);
+		goto fail_free_mem;
+	}
+
+	trace_xfs_buf_get_uncached(bp, _RET_IP_);
+	return bp;
+
+ fail_free_mem:
+	while (--i >= 0)
+		__free_page(bp->b_pages[i]);
+	_xfs_buf_free_pages(bp);
+ fail_free_buf:
+	xfs_buf_free_maps(bp);
+	kmem_zone_free(xfs_buf_zone, bp);
+ fail:
+	return NULL;
+}
+
+/*
+ *	Increment reference count on buffer, to hold the buffer concurrently
+ *	with another thread which may release (free) the buffer asynchronously.
+ *	Must hold the buffer already to call this function.
+ */
+void
+xfs_buf_hold(
+	xfs_buf_t		*bp)
+{
+	trace_xfs_buf_hold(bp, _RET_IP_);
+	atomic_inc(&bp->b_hold);
+}
+
+/*
+ * Release a hold on the specified buffer. If the hold count is 1, the buffer is
+ * placed on LRU or freed (depending on b_lru_ref).
+ */
+void
+xfs_buf_rele(
+	xfs_buf_t		*bp)
+{
+	struct xfs_perag	*pag = bp->b_pag;
+	bool			release;
+	bool			freebuf = false;
+
+	trace_xfs_buf_rele(bp, _RET_IP_);
+
+	if (!pag) {
+		ASSERT(list_empty(&bp->b_lru));
+		if (atomic_dec_and_test(&bp->b_hold)) {
+			xfs_buf_ioacct_dec(bp);
+			xfs_buf_free(bp);
+		}
+		return;
+	}
+
+	ASSERT(atomic_read(&bp->b_hold) > 0);
+
+	/*
+	 * We grab the b_lock here first to serialise racing xfs_buf_rele()
+	 * calls. The pag_buf_lock being taken on the last reference only
+	 * serialises against racing lookups in xfs_buf_find(). IOWs, the second
+	 * to last reference we drop here is not serialised against the last
+	 * reference until we take bp->b_lock. Hence if we don't grab b_lock
+	 * first, the last "release" reference can win the race to the lock and
+	 * free the buffer before the second-to-last reference is processed,
+	 * leading to a use-after-free scenario.
+	 */
+	spin_lock(&bp->b_lock);
+	release = atomic_dec_and_lock(&bp->b_hold, &pag->pag_buf_lock);
+	if (!release) {
+		/*
+		 * Drop the in-flight state if the buffer is already on the LRU
+		 * and it holds the only reference. This is racy because we
+		 * haven't acquired the pag lock, but the use of _XBF_IN_FLIGHT
+		 * ensures the decrement occurs only once per-buf.
+		 */
+		if ((atomic_read(&bp->b_hold) == 1) && !list_empty(&bp->b_lru))
+			__xfs_buf_ioacct_dec(bp);
+		goto out_unlock;
+	}
+
+	/* the last reference has been dropped ... */
+	__xfs_buf_ioacct_dec(bp);
+	if (!(bp->b_flags & XBF_STALE) && atomic_read(&bp->b_lru_ref)) {
+		/*
+		 * If the buffer is added to the LRU take a new reference to the
+		 * buffer for the LRU and clear the (now stale) dispose list
+		 * state flag
+		 */
+		if (list_lru_add(&bp->b_target->bt_lru, &bp->b_lru)) {
+			bp->b_state &= ~XFS_BSTATE_DISPOSE;
+			atomic_inc(&bp->b_hold);
+		}
+		spin_unlock(&pag->pag_buf_lock);
+	} else {
+		/*
+		 * most of the time buffers will already be removed from the
+		 * LRU, so optimise that case by checking for the
+		 * XFS_BSTATE_DISPOSE flag indicating the last list the buffer
+		 * was on was the disposal list
+		 */
+		if (!(bp->b_state & XFS_BSTATE_DISPOSE)) {
+			list_lru_del(&bp->b_target->bt_lru, &bp->b_lru);
+		} else {
+			ASSERT(list_empty(&bp->b_lru));
+		}
+
+		ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
+		rhashtable_remove_fast(&pag->pag_buf_hash, &bp->b_rhash_head,
+				       xfs_buf_hash_params);
+		spin_unlock(&pag->pag_buf_lock);
+		xfs_perag_put(pag);
+		freebuf = true;
+	}
+
+out_unlock:
+	spin_unlock(&bp->b_lock);
+
+	if (freebuf)
+		xfs_buf_free(bp);
+}
+
+
+/*
+ *	Lock a buffer object, if it is not already locked.
+ *
+ *	If we come across a stale, pinned, locked buffer, we know that we are
+ *	being asked to lock a buffer that has been reallocated. Because it is
+ *	pinned, we know that the log has not been pushed to disk and hence it
+ *	will still be locked.  Rather than continuing to have trylock attempts
+ *	fail until someone else pushes the log, push it ourselves before
+ *	returning.  This means that the xfsaild will not get stuck trying
+ *	to push on stale inode buffers.
+ */
+int
+xfs_buf_trylock(
+	struct xfs_buf		*bp)
+{
+	int			locked;
+
+	locked = down_trylock(&bp->b_sema) == 0;
+	if (locked)
+		trace_xfs_buf_trylock(bp, _RET_IP_);
+	else
+		trace_xfs_buf_trylock_fail(bp, _RET_IP_);
+	return locked;
+}
+
+/*
+ *	Lock a buffer object.
+ *
+ *	If we come across a stale, pinned, locked buffer, we know that we
+ *	are being asked to lock a buffer that has been reallocated. Because
+ *	it is pinned, we know that the log has not been pushed to disk and
+ *	hence it will still be locked. Rather than sleeping until someone
+ *	else pushes the log, push it ourselves before trying to get the lock.
+ */
+void
+xfs_buf_lock(
+	struct xfs_buf		*bp)
+{
+	trace_xfs_buf_lock(bp, _RET_IP_);
+
+	if (atomic_read(&bp->b_pin_count) && (bp->b_flags & XBF_STALE))
+		xfs_log_force(bp->b_target->bt_mount, 0);
+	down(&bp->b_sema);
+
+	trace_xfs_buf_lock_done(bp, _RET_IP_);
+}
+
+void
+xfs_buf_unlock(
+	struct xfs_buf		*bp)
+{
+	ASSERT(xfs_buf_islocked(bp));
+
+	up(&bp->b_sema);
+	trace_xfs_buf_unlock(bp, _RET_IP_);
+}
+
+STATIC void
+xfs_buf_wait_unpin(
+	xfs_buf_t		*bp)
+{
+	DECLARE_WAITQUEUE	(wait, current);
+
+	if (atomic_read(&bp->b_pin_count) == 0)
+		return;
+
+	add_wait_queue(&bp->b_waiters, &wait);
+	for (;;) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (atomic_read(&bp->b_pin_count) == 0)
+			break;
+		io_schedule();
+	}
+	remove_wait_queue(&bp->b_waiters, &wait);
+	set_current_state(TASK_RUNNING);
+}
+
+/*
+ *	Buffer Utility Routines
+ */
+
+void
+xfs_buf_ioend(
+	struct xfs_buf	*bp)
+{
+	bool		read = bp->b_flags & XBF_READ;
+
+	trace_xfs_buf_iodone(bp, _RET_IP_);
+
+	bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD);
+
+	/*
+	 * Pull in IO completion errors now. We are guaranteed to be running
+	 * single threaded, so we don't need the lock to read b_io_error.
+	 */
+	if (!bp->b_error && bp->b_io_error)
+		xfs_buf_ioerror(bp, bp->b_io_error);
+
+	/* Only validate buffers that were read without errors */
+	if (read && !bp->b_error && bp->b_ops) {
+		ASSERT(!bp->b_iodone);
+		bp->b_ops->verify_read(bp);
+	}
+
+	if (!bp->b_error) {
+		bp->b_flags &= ~XBF_WRITE_FAIL;
+		bp->b_flags |= XBF_DONE;
+	}
+
+	if (bp->b_iodone)
+		(*(bp->b_iodone))(bp);
+	else if (bp->b_flags & XBF_ASYNC)
+		xfs_buf_relse(bp);
+	else
+		complete(&bp->b_iowait);
+}
+
+static void
+xfs_buf_ioend_work(
+	struct work_struct	*work)
+{
+	struct xfs_buf		*bp =
+		container_of(work, xfs_buf_t, b_ioend_work);
+
+	xfs_buf_ioend(bp);
+}
+
+static void
+xfs_buf_ioend_async(
+	struct xfs_buf	*bp)
+{
+	INIT_WORK(&bp->b_ioend_work, xfs_buf_ioend_work);
+	queue_work(bp->b_ioend_wq, &bp->b_ioend_work);
+}
+
+void
+__xfs_buf_ioerror(
+	xfs_buf_t		*bp,
+	int			error,
+	xfs_failaddr_t		failaddr)
+{
+	ASSERT(error <= 0 && error >= -1000);
+	bp->b_error = error;
+	trace_xfs_buf_ioerror(bp, error, failaddr);
+}
+
+void
+xfs_buf_ioerror_alert(
+	struct xfs_buf		*bp,
+	const char		*func)
+{
+	xfs_alert(bp->b_target->bt_mount,
+"metadata I/O error in \"%s\" at daddr 0x%llx len %d error %d",
+			func, (uint64_t)XFS_BUF_ADDR(bp), bp->b_length,
+			-bp->b_error);
+}
+
+int
+xfs_bwrite(
+	struct xfs_buf		*bp)
+{
+	int			error;
+
+	ASSERT(xfs_buf_islocked(bp));
+
+	bp->b_flags |= XBF_WRITE;
+	bp->b_flags &= ~(XBF_ASYNC | XBF_READ | _XBF_DELWRI_Q |
+			 XBF_DONE);
+
+	error = xfs_buf_submit(bp);
+	if (error) {
+		xfs_force_shutdown(bp->b_target->bt_mount,
+				   SHUTDOWN_META_IO_ERROR);
+	}
+	return error;
+}
+
+static void
+xfs_buf_bio_end_io(
+	struct bio		*bio)
+{
+	struct xfs_buf		*bp = (struct xfs_buf *)bio->bi_private;
+
+	/*
+	 * don't overwrite existing errors - otherwise we can lose errors on
+	 * buffers that require multiple bios to complete.
+	 */
+	if (bio->bi_status) {
+		int error = blk_status_to_errno(bio->bi_status);
+
+		cmpxchg(&bp->b_io_error, 0, error);
+	}
+
+	if (!bp->b_error && xfs_buf_is_vmapped(bp) && (bp->b_flags & XBF_READ))
+		invalidate_kernel_vmap_range(bp->b_addr, xfs_buf_vmap_len(bp));
+
+	if (atomic_dec_and_test(&bp->b_io_remaining) == 1)
+		xfs_buf_ioend_async(bp);
+	bio_put(bio);
+}
+
+static void
+xfs_buf_ioapply_map(
+	struct xfs_buf	*bp,
+	int		map,
+	int		*buf_offset,
+	int		*count,
+	int		op,
+	int		op_flags)
+{
+	int		page_index;
+	int		total_nr_pages = bp->b_page_count;
+	int		nr_pages;
+	struct bio	*bio;
+	sector_t	sector =  bp->b_maps[map].bm_bn;
+	int		size;
+	int		offset;
+
+	/* skip the pages in the buffer before the start offset */
+	page_index = 0;
+	offset = *buf_offset;
+	while (offset >= PAGE_SIZE) {
+		page_index++;
+		offset -= PAGE_SIZE;
+	}
+
+	/*
+	 * Limit the IO size to the length of the current vector, and update the
+	 * remaining IO count for the next time around.
+	 */
+	size = min_t(int, BBTOB(bp->b_maps[map].bm_len), *count);
+	*count -= size;
+	*buf_offset += size;
+
+next_chunk:
+	atomic_inc(&bp->b_io_remaining);
+	nr_pages = min(total_nr_pages, BIO_MAX_PAGES);
+
+	bio = bio_alloc(GFP_NOIO, nr_pages);
+	bio_set_dev(bio, bp->b_target->bt_bdev);
+	bio->bi_iter.bi_sector = sector;
+	bio->bi_end_io = xfs_buf_bio_end_io;
+	bio->bi_private = bp;
+	bio_set_op_attrs(bio, op, op_flags);
+
+	for (; size && nr_pages; nr_pages--, page_index++) {
+		int	rbytes, nbytes = PAGE_SIZE - offset;
+
+		if (nbytes > size)
+			nbytes = size;
+
+		rbytes = bio_add_page(bio, bp->b_pages[page_index], nbytes,
+				      offset);
+		if (rbytes < nbytes)
+			break;
+
+		offset = 0;
+		sector += BTOBB(nbytes);
+		size -= nbytes;
+		total_nr_pages--;
+	}
+
+	if (likely(bio->bi_iter.bi_size)) {
+		if (xfs_buf_is_vmapped(bp)) {
+			flush_kernel_vmap_range(bp->b_addr,
+						xfs_buf_vmap_len(bp));
+		}
+		submit_bio(bio);
+		if (size)
+			goto next_chunk;
+	} else {
+		/*
+		 * This is guaranteed not to be the last io reference count
+		 * because the caller (xfs_buf_submit) holds a count itself.
+		 */
+		atomic_dec(&bp->b_io_remaining);
+		xfs_buf_ioerror(bp, -EIO);
+		bio_put(bio);
+	}
+
+}
+
+STATIC void
+_xfs_buf_ioapply(
+	struct xfs_buf	*bp)
+{
+	struct blk_plug	plug;
+	int		op;
+	int		op_flags = 0;
+	int		offset;
+	int		size;
+	int		i;
+
+	/*
+	 * Make sure we capture only current IO errors rather than stale errors
+	 * left over from previous use of the buffer (e.g. failed readahead).
+	 */
+	bp->b_error = 0;
+
+	/*
+	 * Initialize the I/O completion workqueue if we haven't yet or the
+	 * submitter has not opted to specify a custom one.
+	 */
+	if (!bp->b_ioend_wq)
+		bp->b_ioend_wq = bp->b_target->bt_mount->m_buf_workqueue;
+
+	if (bp->b_flags & XBF_WRITE) {
+		op = REQ_OP_WRITE;
+		if (bp->b_flags & XBF_SYNCIO)
+			op_flags = REQ_SYNC;
+		if (bp->b_flags & XBF_FUA)
+			op_flags |= REQ_FUA;
+		if (bp->b_flags & XBF_FLUSH)
+			op_flags |= REQ_PREFLUSH;
+
+		/*
+		 * Run the write verifier callback function if it exists. If
+		 * this function fails it will mark the buffer with an error and
+		 * the IO should not be dispatched.
+		 */
+		if (bp->b_ops) {
+			bp->b_ops->verify_write(bp);
+			if (bp->b_error) {
+				xfs_force_shutdown(bp->b_target->bt_mount,
+						   SHUTDOWN_CORRUPT_INCORE);
+				return;
+			}
+		} else if (bp->b_bn != XFS_BUF_DADDR_NULL) {
+			struct xfs_mount *mp = bp->b_target->bt_mount;
+
+			/*
+			 * non-crc filesystems don't attach verifiers during
+			 * log recovery, so don't warn for such filesystems.
+			 */
+			if (xfs_sb_version_hascrc(&mp->m_sb)) {
+				xfs_warn(mp,
+					"%s: no buf ops on daddr 0x%llx len %d",
+					__func__, bp->b_bn, bp->b_length);
+				xfs_hex_dump(bp->b_addr,
+						XFS_CORRUPTION_DUMP_LEN);
+				dump_stack();
+			}
+		}
+	} else if (bp->b_flags & XBF_READ_AHEAD) {
+		op = REQ_OP_READ;
+		op_flags = REQ_RAHEAD;
+	} else {
+		op = REQ_OP_READ;
+	}
+
+	/* we only use the buffer cache for meta-data */
+	op_flags |= REQ_META;
+
+	/*
+	 * Walk all the vectors issuing IO on them. Set up the initial offset
+	 * into the buffer and the desired IO size before we start -
+	 * _xfs_buf_ioapply_vec() will modify them appropriately for each
+	 * subsequent call.
+	 */
+	offset = bp->b_offset;
+	size = BBTOB(bp->b_io_length);
+	blk_start_plug(&plug);
+	for (i = 0; i < bp->b_map_count; i++) {
+		xfs_buf_ioapply_map(bp, i, &offset, &size, op, op_flags);
+		if (bp->b_error)
+			break;
+		if (size <= 0)
+			break;	/* all done */
+	}
+	blk_finish_plug(&plug);
+}
+
+/*
+ * Wait for I/O completion of a sync buffer and return the I/O error code.
+ */
+static int
+xfs_buf_iowait(
+	struct xfs_buf	*bp)
+{
+	ASSERT(!(bp->b_flags & XBF_ASYNC));
+
+	trace_xfs_buf_iowait(bp, _RET_IP_);
+	wait_for_completion(&bp->b_iowait);
+	trace_xfs_buf_iowait_done(bp, _RET_IP_);
+
+	return bp->b_error;
+}
+
+/*
+ * Buffer I/O submission path, read or write. Asynchronous submission transfers
+ * the buffer lock ownership and the current reference to the IO. It is not
+ * safe to reference the buffer after a call to this function unless the caller
+ * holds an additional reference itself.
+ */
+int
+__xfs_buf_submit(
+	struct xfs_buf	*bp,
+	bool		wait)
+{
+	int		error = 0;
+
+	trace_xfs_buf_submit(bp, _RET_IP_);
+
+	ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
+
+	/* on shutdown we stale and complete the buffer immediately */
+	if (XFS_FORCED_SHUTDOWN(bp->b_target->bt_mount)) {
+		xfs_buf_ioerror(bp, -EIO);
+		bp->b_flags &= ~XBF_DONE;
+		xfs_buf_stale(bp);
+		xfs_buf_ioend(bp);
+		return -EIO;
+	}
+
+	/*
+	 * Grab a reference so the buffer does not go away underneath us. For
+	 * async buffers, I/O completion drops the callers reference, which
+	 * could occur before submission returns.
+	 */
+	xfs_buf_hold(bp);
+
+	if (bp->b_flags & XBF_WRITE)
+		xfs_buf_wait_unpin(bp);
+
+	/* clear the internal error state to avoid spurious errors */
+	bp->b_io_error = 0;
+
+	/*
+	 * Set the count to 1 initially, this will stop an I/O completion
+	 * callout which happens before we have started all the I/O from calling
+	 * xfs_buf_ioend too early.
+	 */
+	atomic_set(&bp->b_io_remaining, 1);
+	if (bp->b_flags & XBF_ASYNC)
+		xfs_buf_ioacct_inc(bp);
+	_xfs_buf_ioapply(bp);
+
+	/*
+	 * If _xfs_buf_ioapply failed, we can get back here with only the IO
+	 * reference we took above. If we drop it to zero, run completion so
+	 * that we don't return to the caller with completion still pending.
+	 */
+	if (atomic_dec_and_test(&bp->b_io_remaining) == 1) {
+		if (bp->b_error || !(bp->b_flags & XBF_ASYNC))
+			xfs_buf_ioend(bp);
+		else
+			xfs_buf_ioend_async(bp);
+	}
+
+	if (wait)
+		error = xfs_buf_iowait(bp);
+
+	/*
+	 * Release the hold that keeps the buffer referenced for the entire
+	 * I/O. Note that if the buffer is async, it is not safe to reference
+	 * after this release.
+	 */
+	xfs_buf_rele(bp);
+	return error;
+}
+
+void *
+xfs_buf_offset(
+	struct xfs_buf		*bp,
+	size_t			offset)
+{
+	struct page		*page;
+
+	if (bp->b_addr)
+		return bp->b_addr + offset;
+
+	offset += bp->b_offset;
+	page = bp->b_pages[offset >> PAGE_SHIFT];
+	return page_address(page) + (offset & (PAGE_SIZE-1));
+}
+
+/*
+ *	Move data into or out of a buffer.
+ */
+void
+xfs_buf_iomove(
+	xfs_buf_t		*bp,	/* buffer to process		*/
+	size_t			boff,	/* starting buffer offset	*/
+	size_t			bsize,	/* length to copy		*/
+	void			*data,	/* data address			*/
+	xfs_buf_rw_t		mode)	/* read/write/zero flag		*/
+{
+	size_t			bend;
+
+	bend = boff + bsize;
+	while (boff < bend) {
+		struct page	*page;
+		int		page_index, page_offset, csize;
+
+		page_index = (boff + bp->b_offset) >> PAGE_SHIFT;
+		page_offset = (boff + bp->b_offset) & ~PAGE_MASK;
+		page = bp->b_pages[page_index];
+		csize = min_t(size_t, PAGE_SIZE - page_offset,
+				      BBTOB(bp->b_io_length) - boff);
+
+		ASSERT((csize + page_offset) <= PAGE_SIZE);
+
+		switch (mode) {
+		case XBRW_ZERO:
+			memset(page_address(page) + page_offset, 0, csize);
+			break;
+		case XBRW_READ:
+			memcpy(data, page_address(page) + page_offset, csize);
+			break;
+		case XBRW_WRITE:
+			memcpy(page_address(page) + page_offset, data, csize);
+		}
+
+		boff += csize;
+		data += csize;
+	}
+}
+
+/*
+ *	Handling of buffer targets (buftargs).
+ */
+
+/*
+ * Wait for any bufs with callbacks that have been submitted but have not yet
+ * returned. These buffers will have an elevated hold count, so wait on those
+ * while freeing all the buffers only held by the LRU.
+ */
+static enum lru_status
+xfs_buftarg_wait_rele(
+	struct list_head	*item,
+	struct list_lru_one	*lru,
+	spinlock_t		*lru_lock,
+	void			*arg)
+
+{
+	struct xfs_buf		*bp = container_of(item, struct xfs_buf, b_lru);
+	struct list_head	*dispose = arg;
+
+	if (atomic_read(&bp->b_hold) > 1) {
+		/* need to wait, so skip it this pass */
+		trace_xfs_buf_wait_buftarg(bp, _RET_IP_);
+		return LRU_SKIP;
+	}
+	if (!spin_trylock(&bp->b_lock))
+		return LRU_SKIP;
+
+	/*
+	 * clear the LRU reference count so the buffer doesn't get
+	 * ignored in xfs_buf_rele().
+	 */
+	atomic_set(&bp->b_lru_ref, 0);
+	bp->b_state |= XFS_BSTATE_DISPOSE;
+	list_lru_isolate_move(lru, item, dispose);
+	spin_unlock(&bp->b_lock);
+	return LRU_REMOVED;
+}
+
+void
+xfs_wait_buftarg(
+	struct xfs_buftarg	*btp)
+{
+	LIST_HEAD(dispose);
+	int loop = 0;
+
+	/*
+	 * First wait on the buftarg I/O count for all in-flight buffers to be
+	 * released. This is critical as new buffers do not make the LRU until
+	 * they are released.
+	 *
+	 * Next, flush the buffer workqueue to ensure all completion processing
+	 * has finished. Just waiting on buffer locks is not sufficient for
+	 * async IO as the reference count held over IO is not released until
+	 * after the buffer lock is dropped. Hence we need to ensure here that
+	 * all reference counts have been dropped before we start walking the
+	 * LRU list.
+	 */
+	while (percpu_counter_sum(&btp->bt_io_count))
+		delay(100);
+	flush_workqueue(btp->bt_mount->m_buf_workqueue);
+
+	/* loop until there is nothing left on the lru list. */
+	while (list_lru_count(&btp->bt_lru)) {
+		list_lru_walk(&btp->bt_lru, xfs_buftarg_wait_rele,
+			      &dispose, LONG_MAX);
+
+		while (!list_empty(&dispose)) {
+			struct xfs_buf *bp;
+			bp = list_first_entry(&dispose, struct xfs_buf, b_lru);
+			list_del_init(&bp->b_lru);
+			if (bp->b_flags & XBF_WRITE_FAIL) {
+				xfs_alert(btp->bt_mount,
+"Corruption Alert: Buffer at daddr 0x%llx had permanent write failures!",
+					(long long)bp->b_bn);
+				xfs_alert(btp->bt_mount,
+"Please run xfs_repair to determine the extent of the problem.");
+			}
+			xfs_buf_rele(bp);
+		}
+		if (loop++ != 0)
+			delay(100);
+	}
+}
+
+static enum lru_status
+xfs_buftarg_isolate(
+	struct list_head	*item,
+	struct list_lru_one	*lru,
+	spinlock_t		*lru_lock,
+	void			*arg)
+{
+	struct xfs_buf		*bp = container_of(item, struct xfs_buf, b_lru);
+	struct list_head	*dispose = arg;
+
+	/*
+	 * we are inverting the lru lock/bp->b_lock here, so use a trylock.
+	 * If we fail to get the lock, just skip it.
+	 */
+	if (!spin_trylock(&bp->b_lock))
+		return LRU_SKIP;
+	/*
+	 * Decrement the b_lru_ref count unless the value is already
+	 * zero. If the value is already zero, we need to reclaim the
+	 * buffer, otherwise it gets another trip through the LRU.
+	 */
+	if (atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
+		spin_unlock(&bp->b_lock);
+		return LRU_ROTATE;
+	}
+
+	bp->b_state |= XFS_BSTATE_DISPOSE;
+	list_lru_isolate_move(lru, item, dispose);
+	spin_unlock(&bp->b_lock);
+	return LRU_REMOVED;
+}
+
+static unsigned long
+xfs_buftarg_shrink_scan(
+	struct shrinker		*shrink,
+	struct shrink_control	*sc)
+{
+	struct xfs_buftarg	*btp = container_of(shrink,
+					struct xfs_buftarg, bt_shrinker);
+	LIST_HEAD(dispose);
+	unsigned long		freed;
+
+	freed = list_lru_shrink_walk(&btp->bt_lru, sc,
+				     xfs_buftarg_isolate, &dispose);
+
+	while (!list_empty(&dispose)) {
+		struct xfs_buf *bp;
+		bp = list_first_entry(&dispose, struct xfs_buf, b_lru);
+		list_del_init(&bp->b_lru);
+		xfs_buf_rele(bp);
+	}
+
+	return freed;
+}
+
+static unsigned long
+xfs_buftarg_shrink_count(
+	struct shrinker		*shrink,
+	struct shrink_control	*sc)
+{
+	struct xfs_buftarg	*btp = container_of(shrink,
+					struct xfs_buftarg, bt_shrinker);
+	return list_lru_shrink_count(&btp->bt_lru, sc);
+}
+
+void
+xfs_free_buftarg(
+	struct xfs_buftarg	*btp)
+{
+	unregister_shrinker(&btp->bt_shrinker);
+	ASSERT(percpu_counter_sum(&btp->bt_io_count) == 0);
+	percpu_counter_destroy(&btp->bt_io_count);
+	list_lru_destroy(&btp->bt_lru);
+
+	xfs_blkdev_issue_flush(btp);
+
+	kmem_free(btp);
+}
+
+int
+xfs_setsize_buftarg(
+	xfs_buftarg_t		*btp,
+	unsigned int		sectorsize)
+{
+	/* Set up metadata sector size info */
+	btp->bt_meta_sectorsize = sectorsize;
+	btp->bt_meta_sectormask = sectorsize - 1;
+
+	if (set_blocksize(btp->bt_bdev, sectorsize)) {
+		xfs_warn(btp->bt_mount,
+			"Cannot set_blocksize to %u on device %pg",
+			sectorsize, btp->bt_bdev);
+		return -EINVAL;
+	}
+
+	/* Set up device logical sector size mask */
+	btp->bt_logical_sectorsize = bdev_logical_block_size(btp->bt_bdev);
+	btp->bt_logical_sectormask = bdev_logical_block_size(btp->bt_bdev) - 1;
+
+	return 0;
+}
+
+/*
+ * When allocating the initial buffer target we have not yet
+ * read in the superblock, so don't know what sized sectors
+ * are being used at this early stage.  Play safe.
+ */
+STATIC int
+xfs_setsize_buftarg_early(
+	xfs_buftarg_t		*btp,
+	struct block_device	*bdev)
+{
+	return xfs_setsize_buftarg(btp, bdev_logical_block_size(bdev));
+}
+
+xfs_buftarg_t *
+xfs_alloc_buftarg(
+	struct xfs_mount	*mp,
+	struct block_device	*bdev,
+	struct dax_device	*dax_dev)
+{
+	xfs_buftarg_t		*btp;
+
+	btp = kmem_zalloc(sizeof(*btp), KM_SLEEP | KM_NOFS);
+
+	btp->bt_mount = mp;
+	btp->bt_dev =  bdev->bd_dev;
+	btp->bt_bdev = bdev;
+	btp->bt_daxdev = dax_dev;
+
+	if (xfs_setsize_buftarg_early(btp, bdev))
+		goto error_free;
+
+	if (list_lru_init(&btp->bt_lru))
+		goto error_free;
+
+	if (percpu_counter_init(&btp->bt_io_count, 0, GFP_KERNEL))
+		goto error_lru;
+
+	btp->bt_shrinker.count_objects = xfs_buftarg_shrink_count;
+	btp->bt_shrinker.scan_objects = xfs_buftarg_shrink_scan;
+	btp->bt_shrinker.seeks = DEFAULT_SEEKS;
+	btp->bt_shrinker.flags = SHRINKER_NUMA_AWARE;
+	if (register_shrinker(&btp->bt_shrinker))
+		goto error_pcpu;
+	return btp;
+
+error_pcpu:
+	percpu_counter_destroy(&btp->bt_io_count);
+error_lru:
+	list_lru_destroy(&btp->bt_lru);
+error_free:
+	kmem_free(btp);
+	return NULL;
+}
+
+/*
+ * Cancel a delayed write list.
+ *
+ * Remove each buffer from the list, clear the delwri queue flag and drop the
+ * associated buffer reference.
+ */
+void
+xfs_buf_delwri_cancel(
+	struct list_head	*list)
+{
+	struct xfs_buf		*bp;
+
+	while (!list_empty(list)) {
+		bp = list_first_entry(list, struct xfs_buf, b_list);
+
+		xfs_buf_lock(bp);
+		bp->b_flags &= ~_XBF_DELWRI_Q;
+		list_del_init(&bp->b_list);
+		xfs_buf_relse(bp);
+	}
+}
+
+/*
+ * Add a buffer to the delayed write list.
+ *
+ * This queues a buffer for writeout if it hasn't already been.  Note that
+ * neither this routine nor the buffer list submission functions perform
+ * any internal synchronization.  It is expected that the lists are thread-local
+ * to the callers.
+ *
+ * Returns true if we queued up the buffer, or false if it already had
+ * been on the buffer list.
+ */
+bool
+xfs_buf_delwri_queue(
+	struct xfs_buf		*bp,
+	struct list_head	*list)
+{
+	ASSERT(xfs_buf_islocked(bp));
+	ASSERT(!(bp->b_flags & XBF_READ));
+
+	/*
+	 * If the buffer is already marked delwri it already is queued up
+	 * by someone else for imediate writeout.  Just ignore it in that
+	 * case.
+	 */
+	if (bp->b_flags & _XBF_DELWRI_Q) {
+		trace_xfs_buf_delwri_queued(bp, _RET_IP_);
+		return false;
+	}
+
+	trace_xfs_buf_delwri_queue(bp, _RET_IP_);
+
+	/*
+	 * If a buffer gets written out synchronously or marked stale while it
+	 * is on a delwri list we lazily remove it. To do this, the other party
+	 * clears the  _XBF_DELWRI_Q flag but otherwise leaves the buffer alone.
+	 * It remains referenced and on the list.  In a rare corner case it
+	 * might get readded to a delwri list after the synchronous writeout, in
+	 * which case we need just need to re-add the flag here.
+	 */
+	bp->b_flags |= _XBF_DELWRI_Q;
+	if (list_empty(&bp->b_list)) {
+		atomic_inc(&bp->b_hold);
+		list_add_tail(&bp->b_list, list);
+	}
+
+	return true;
+}
+
+/*
+ * Compare function is more complex than it needs to be because
+ * the return value is only 32 bits and we are doing comparisons
+ * on 64 bit values
+ */
+static int
+xfs_buf_cmp(
+	void		*priv,
+	struct list_head *a,
+	struct list_head *b)
+{
+	struct xfs_buf	*ap = container_of(a, struct xfs_buf, b_list);
+	struct xfs_buf	*bp = container_of(b, struct xfs_buf, b_list);
+	xfs_daddr_t		diff;
+
+	diff = ap->b_maps[0].bm_bn - bp->b_maps[0].bm_bn;
+	if (diff < 0)
+		return -1;
+	if (diff > 0)
+		return 1;
+	return 0;
+}
+
+/*
+ * Submit buffers for write. If wait_list is specified, the buffers are
+ * submitted using sync I/O and placed on the wait list such that the caller can
+ * iowait each buffer. Otherwise async I/O is used and the buffers are released
+ * at I/O completion time. In either case, buffers remain locked until I/O
+ * completes and the buffer is released from the queue.
+ */
+static int
+xfs_buf_delwri_submit_buffers(
+	struct list_head	*buffer_list,
+	struct list_head	*wait_list)
+{
+	struct xfs_buf		*bp, *n;
+	LIST_HEAD		(submit_list);
+	int			pinned = 0;
+	struct blk_plug		plug;
+
+	list_sort(NULL, buffer_list, xfs_buf_cmp);
+
+	blk_start_plug(&plug);
+	list_for_each_entry_safe(bp, n, buffer_list, b_list) {
+		if (!wait_list) {
+			if (xfs_buf_ispinned(bp)) {
+				pinned++;
+				continue;
+			}
+			if (!xfs_buf_trylock(bp))
+				continue;
+		} else {
+			xfs_buf_lock(bp);
+		}
+
+		/*
+		 * Someone else might have written the buffer synchronously or
+		 * marked it stale in the meantime.  In that case only the
+		 * _XBF_DELWRI_Q flag got cleared, and we have to drop the
+		 * reference and remove it from the list here.
+		 */
+		if (!(bp->b_flags & _XBF_DELWRI_Q)) {
+			list_del_init(&bp->b_list);
+			xfs_buf_relse(bp);
+			continue;
+		}
+
+		trace_xfs_buf_delwri_split(bp, _RET_IP_);
+
+		/*
+		 * If we have a wait list, each buffer (and associated delwri
+		 * queue reference) transfers to it and is submitted
+		 * synchronously. Otherwise, drop the buffer from the delwri
+		 * queue and submit async.
+		 */
+		bp->b_flags &= ~_XBF_DELWRI_Q;
+		bp->b_flags |= XBF_WRITE;
+		if (wait_list) {
+			bp->b_flags &= ~XBF_ASYNC;
+			list_move_tail(&bp->b_list, wait_list);
+		} else {
+			bp->b_flags |= XBF_ASYNC;
+			list_del_init(&bp->b_list);
+		}
+		__xfs_buf_submit(bp, false);
+	}
+	blk_finish_plug(&plug);
+
+	return pinned;
+}
+
+/*
+ * Write out a buffer list asynchronously.
+ *
+ * This will take the @buffer_list, write all non-locked and non-pinned buffers
+ * out and not wait for I/O completion on any of the buffers.  This interface
+ * is only safely useable for callers that can track I/O completion by higher
+ * level means, e.g. AIL pushing as the @buffer_list is consumed in this
+ * function.
+ *
+ * Note: this function will skip buffers it would block on, and in doing so
+ * leaves them on @buffer_list so they can be retried on a later pass. As such,
+ * it is up to the caller to ensure that the buffer list is fully submitted or
+ * cancelled appropriately when they are finished with the list. Failure to
+ * cancel or resubmit the list until it is empty will result in leaked buffers
+ * at unmount time.
+ */
+int
+xfs_buf_delwri_submit_nowait(
+	struct list_head	*buffer_list)
+{
+	return xfs_buf_delwri_submit_buffers(buffer_list, NULL);
+}
+
+/*
+ * Write out a buffer list synchronously.
+ *
+ * This will take the @buffer_list, write all buffers out and wait for I/O
+ * completion on all of the buffers. @buffer_list is consumed by the function,
+ * so callers must have some other way of tracking buffers if they require such
+ * functionality.
+ */
+int
+xfs_buf_delwri_submit(
+	struct list_head	*buffer_list)
+{
+	LIST_HEAD		(wait_list);
+	int			error = 0, error2;
+	struct xfs_buf		*bp;
+
+	xfs_buf_delwri_submit_buffers(buffer_list, &wait_list);
+
+	/* Wait for IO to complete. */
+	while (!list_empty(&wait_list)) {
+		bp = list_first_entry(&wait_list, struct xfs_buf, b_list);
+
+		list_del_init(&bp->b_list);
+
+		/*
+		 * Wait on the locked buffer, check for errors and unlock and
+		 * release the delwri queue reference.
+		 */
+		error2 = xfs_buf_iowait(bp);
+		xfs_buf_relse(bp);
+		if (!error)
+			error = error2;
+	}
+
+	return error;
+}
+
+/*
+ * Push a single buffer on a delwri queue.
+ *
+ * The purpose of this function is to submit a single buffer of a delwri queue
+ * and return with the buffer still on the original queue. The waiting delwri
+ * buffer submission infrastructure guarantees transfer of the delwri queue
+ * buffer reference to a temporary wait list. We reuse this infrastructure to
+ * transfer the buffer back to the original queue.
+ *
+ * Note the buffer transitions from the queued state, to the submitted and wait
+ * listed state and back to the queued state during this call. The buffer
+ * locking and queue management logic between _delwri_pushbuf() and
+ * _delwri_queue() guarantee that the buffer cannot be queued to another list
+ * before returning.
+ */
+int
+xfs_buf_delwri_pushbuf(
+	struct xfs_buf		*bp,
+	struct list_head	*buffer_list)
+{
+	LIST_HEAD		(submit_list);
+	int			error;
+
+	ASSERT(bp->b_flags & _XBF_DELWRI_Q);
+
+	trace_xfs_buf_delwri_pushbuf(bp, _RET_IP_);
+
+	/*
+	 * Isolate the buffer to a new local list so we can submit it for I/O
+	 * independently from the rest of the original list.
+	 */
+	xfs_buf_lock(bp);
+	list_move(&bp->b_list, &submit_list);
+	xfs_buf_unlock(bp);
+
+	/*
+	 * Delwri submission clears the DELWRI_Q buffer flag and returns with
+	 * the buffer on the wait list with the original reference. Rather than
+	 * bounce the buffer from a local wait list back to the original list
+	 * after I/O completion, reuse the original list as the wait list.
+	 */
+	xfs_buf_delwri_submit_buffers(&submit_list, buffer_list);
+
+	/*
+	 * The buffer is now locked, under I/O and wait listed on the original
+	 * delwri queue. Wait for I/O completion, restore the DELWRI_Q flag and
+	 * return with the buffer unlocked and on the original queue.
+	 */
+	error = xfs_buf_iowait(bp);
+	bp->b_flags |= _XBF_DELWRI_Q;
+	xfs_buf_unlock(bp);
+
+	return error;
+}
+
+int __init
+xfs_buf_init(void)
+{
+	xfs_buf_zone = kmem_zone_init_flags(sizeof(xfs_buf_t), "xfs_buf",
+						KM_ZONE_HWALIGN, NULL);
+	if (!xfs_buf_zone)
+		goto out;
+
+	return 0;
+
+ out:
+	return -ENOMEM;
+}
+
+void
+xfs_buf_terminate(void)
+{
+	kmem_zone_destroy(xfs_buf_zone);
+}
+
+void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref)
+{
+	/*
+	 * Set the lru reference count to 0 based on the error injection tag.
+	 * This allows userspace to disrupt buffer caching for debug/testing
+	 * purposes.
+	 */
+	if (XFS_TEST_ERROR(false, bp->b_target->bt_mount,
+			   XFS_ERRTAG_BUF_LRU_REF))
+		lru_ref = 0;
+
+	atomic_set(&bp->b_lru_ref, lru_ref);
+}