Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 2376 insertions, 0 deletions

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
new file mode 100644
index 0000000000..c1ece4a08f
--- /dev/null
+++ b/fs/xfs/xfs_buf.c
@@ -0,0 +1,2376 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2000-2006 Silicon Graphics, Inc.
+ * All Rights Reserved.
+ */
+#include "xfs.h"
+#include <linux/backing-dev.h>
+#include <linux/dax.h>
+
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_trace.h"
+#include "xfs_log.h"
+#include "xfs_log_recover.h"
+#include "xfs_log_priv.h"
+#include "xfs_trans.h"
+#include "xfs_buf_item.h"
+#include "xfs_errortag.h"
+#include "xfs_error.h"
+#include "xfs_ag.h"
+
+struct kmem_cache *xfs_buf_cache;
+
+/*
+ * 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_drain_rele
+ *	lru_lock
+ *	  b_lock (trylock due to inversion)
+ *
+ * xfs_buftarg_isolate
+ *	lru_lock
+ *	  b_lock (trylock due to inversion)
+ */
+
+static int __xfs_buf_submit(struct xfs_buf *bp, bool wait);
+
+static inline int
+xfs_buf_submit(
+	struct xfs_buf		*bp)
+{
+	return __xfs_buf_submit(bp, !(bp->b_flags & XBF_ASYNC));
+}
+
+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);
+}
+
+/*
+ * 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_buftarg_drain()), 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;
+	}
+}
+
+static int
+_xfs_buf_alloc(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_buf		*bp;
+	int			error;
+	int			i;
+
+	*bpp = NULL;
+	bp = kmem_cache_zalloc(xfs_buf_cache, GFP_NOFS | __GFP_NOFAIL);
+
+	/*
+	 * 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_mount = target->bt_mount;
+	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_cache_free(xfs_buf_cache, bp);
+		return error;
+	}
+
+	bp->b_rhash_key = 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;
+	}
+
+	atomic_set(&bp->b_pin_count, 0);
+	init_waitqueue_head(&bp->b_waiters);
+
+	XFS_STATS_INC(bp->b_mount, xb_create);
+	trace_xfs_buf_init(bp, _RET_IP_);
+
+	*bpp = bp;
+	return 0;
+}
+
+static void
+xfs_buf_free_pages(
+	struct xfs_buf	*bp)
+{
+	uint		i;
+
+	ASSERT(bp->b_flags & _XBF_PAGES);
+
+	if (xfs_buf_is_vmapped(bp))
+		vm_unmap_ram(bp->b_addr, bp->b_page_count);
+
+	for (i = 0; i < bp->b_page_count; i++) {
+		if (bp->b_pages[i])
+			__free_page(bp->b_pages[i]);
+	}
+	mm_account_reclaimed_pages(bp->b_page_count);
+
+	if (bp->b_pages != bp->b_page_array)
+		kmem_free(bp->b_pages);
+	bp->b_pages = NULL;
+	bp->b_flags &= ~_XBF_PAGES;
+}
+
+static void
+xfs_buf_free_callback(
+	struct callback_head	*cb)
+{
+	struct xfs_buf		*bp = container_of(cb, struct xfs_buf, b_rcu);
+
+	xfs_buf_free_maps(bp);
+	kmem_cache_free(xfs_buf_cache, bp);
+}
+
+static void
+xfs_buf_free(
+	struct xfs_buf		*bp)
+{
+	trace_xfs_buf_free(bp, _RET_IP_);
+
+	ASSERT(list_empty(&bp->b_lru));
+
+	if (bp->b_flags & _XBF_PAGES)
+		xfs_buf_free_pages(bp);
+	else if (bp->b_flags & _XBF_KMEM)
+		kmem_free(bp->b_addr);
+
+	call_rcu(&bp->b_rcu, xfs_buf_free_callback);
+}
+
+static int
+xfs_buf_alloc_kmem(
+	struct xfs_buf	*bp,
+	xfs_buf_flags_t	flags)
+{
+	xfs_km_flags_t	kmflag_mask = KM_NOFS;
+	size_t		size = BBTOB(bp->b_length);
+
+	/* Assure zeroed buffer for non-read cases. */
+	if (!(flags & XBF_READ))
+		kmflag_mask |= KM_ZERO;
+
+	bp->b_addr = kmem_alloc(size, kmflag_mask);
+	if (!bp->b_addr)
+		return -ENOMEM;
+
+	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;
+		return -ENOMEM;
+	}
+	bp->b_offset = offset_in_page(bp->b_addr);
+	bp->b_pages = bp->b_page_array;
+	bp->b_pages[0] = kmem_to_page(bp->b_addr);
+	bp->b_page_count = 1;
+	bp->b_flags |= _XBF_KMEM;
+	return 0;
+}
+
+static int
+xfs_buf_alloc_pages(
+	struct xfs_buf	*bp,
+	xfs_buf_flags_t	flags)
+{
+	gfp_t		gfp_mask = __GFP_NOWARN;
+	long		filled = 0;
+
+	if (flags & XBF_READ_AHEAD)
+		gfp_mask |= __GFP_NORETRY;
+	else
+		gfp_mask |= GFP_NOFS;
+
+	/* Make sure that we have a page list */
+	bp->b_page_count = DIV_ROUND_UP(BBTOB(bp->b_length), PAGE_SIZE);
+	if (bp->b_page_count <= XB_PAGES) {
+		bp->b_pages = bp->b_page_array;
+	} else {
+		bp->b_pages = kzalloc(sizeof(struct page *) * bp->b_page_count,
+					gfp_mask);
+		if (!bp->b_pages)
+			return -ENOMEM;
+	}
+	bp->b_flags |= _XBF_PAGES;
+
+	/* Assure zeroed buffer for non-read cases. */
+	if (!(flags & XBF_READ))
+		gfp_mask |= __GFP_ZERO;
+
+	/*
+	 * Bulk filling of pages can take multiple calls. Not filling the entire
+	 * array is not an allocation failure, so don't back off if we get at
+	 * least one extra page.
+	 */
+	for (;;) {
+		long	last = filled;
+
+		filled = alloc_pages_bulk_array(gfp_mask, bp->b_page_count,
+						bp->b_pages);
+		if (filled == bp->b_page_count) {
+			XFS_STATS_INC(bp->b_mount, xb_page_found);
+			break;
+		}
+
+		if (filled != last)
+			continue;
+
+		if (flags & XBF_READ_AHEAD) {
+			xfs_buf_free_pages(bp);
+			return -ENOMEM;
+		}
+
+		XFS_STATS_INC(bp->b_mount, xb_page_retries);
+		memalloc_retry_wait(gfp_mask);
+	}
+	return 0;
+}
+
+/*
+ *	Map buffer into kernel address-space if necessary.
+ */
+STATIC int
+_xfs_buf_map_pages(
+	struct xfs_buf		*bp,
+	xfs_buf_flags_t		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]);
+	} else if (flags & XBF_UNMAPPED) {
+		bp->b_addr = NULL;
+	} else {
+		int retried = 0;
+		unsigned nofs_flag;
+
+		/*
+		 * vm_map_ram() will allocate auxiliary 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);
+			if (bp->b_addr)
+				break;
+			vm_unmap_aliases();
+		} while (retried++ <= 1);
+		memalloc_nofs_restore(nofs_flag);
+
+		if (!bp->b_addr)
+			return -ENOMEM;
+	}
+
+	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_rhash_key != 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.
+		 */
+		if (!(map->bm_flags & XBM_LIVESCAN))
+			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_rhash_key),
+	.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);
+}
+
+static int
+xfs_buf_map_verify(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*map)
+{
+	xfs_daddr_t		eofs;
+
+	/* Check for IOs smaller than the sector size / not sector aligned */
+	ASSERT(!(BBTOB(map->bm_len) < btp->bt_meta_sectorsize));
+	ASSERT(!(BBTOB(map->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 (map->bm_bn < 0 || map->bm_bn >= eofs) {
+		xfs_alert(btp->bt_mount,
+			  "%s: daddr 0x%llx out of range, EOFS 0x%llx",
+			  __func__, map->bm_bn, eofs);
+		WARN_ON(1);
+		return -EFSCORRUPTED;
+	}
+	return 0;
+}
+
+static int
+xfs_buf_find_lock(
+	struct xfs_buf          *bp,
+	xfs_buf_flags_t		flags)
+{
+	if (flags & XBF_TRYLOCK) {
+		if (!xfs_buf_trylock(bp)) {
+			XFS_STATS_INC(bp->b_mount, xb_busy_locked);
+			return -EAGAIN;
+		}
+	} else {
+		xfs_buf_lock(bp);
+		XFS_STATS_INC(bp->b_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) {
+		if (flags & XBF_LIVESCAN) {
+			xfs_buf_unlock(bp);
+			return -ENOENT;
+		}
+		ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
+		bp->b_flags &= _XBF_KMEM | _XBF_PAGES;
+		bp->b_ops = NULL;
+	}
+	return 0;
+}
+
+static inline int
+xfs_buf_lookup(
+	struct xfs_perag	*pag,
+	struct xfs_buf_map	*map,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_buf          *bp;
+	int			error;
+
+	rcu_read_lock();
+	bp = rhashtable_lookup(&pag->pag_buf_hash, map, xfs_buf_hash_params);
+	if (!bp || !atomic_inc_not_zero(&bp->b_hold)) {
+		rcu_read_unlock();
+		return -ENOENT;
+	}
+	rcu_read_unlock();
+
+	error = xfs_buf_find_lock(bp, flags);
+	if (error) {
+		xfs_buf_rele(bp);
+		return error;
+	}
+
+	trace_xfs_buf_find(bp, flags, _RET_IP_);
+	*bpp = bp;
+	return 0;
+}
+
+/*
+ * Insert the new_bp into the hash table. This consumes the perag reference
+ * taken for the lookup regardless of the result of the insert.
+ */
+static int
+xfs_buf_find_insert(
+	struct xfs_buftarg	*btp,
+	struct xfs_perag	*pag,
+	struct xfs_buf_map	*cmap,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_buf		*new_bp;
+	struct xfs_buf		*bp;
+	int			error;
+
+	error = _xfs_buf_alloc(btp, map, nmaps, flags, &new_bp);
+	if (error)
+		goto out_drop_pag;
+
+	/*
+	 * For buffers that fit entirely within a single page, first attempt to
+	 * allocate the memory from the heap to minimise memory usage. If we
+	 * can't get heap memory for these small buffers, we fall back to using
+	 * the page allocator.
+	 */
+	if (BBTOB(new_bp->b_length) >= PAGE_SIZE ||
+	    xfs_buf_alloc_kmem(new_bp, flags) < 0) {
+		error = xfs_buf_alloc_pages(new_bp, flags);
+		if (error)
+			goto out_free_buf;
+	}
+
+	spin_lock(&pag->pag_buf_lock);
+	bp = rhashtable_lookup_get_insert_fast(&pag->pag_buf_hash,
+			&new_bp->b_rhash_head, xfs_buf_hash_params);
+	if (IS_ERR(bp)) {
+		error = PTR_ERR(bp);
+		spin_unlock(&pag->pag_buf_lock);
+		goto out_free_buf;
+	}
+	if (bp) {
+		/* found an existing buffer */
+		atomic_inc(&bp->b_hold);
+		spin_unlock(&pag->pag_buf_lock);
+		error = xfs_buf_find_lock(bp, flags);
+		if (error)
+			xfs_buf_rele(bp);
+		else
+			*bpp = bp;
+		goto out_free_buf;
+	}
+
+	/* The new buffer keeps the perag reference until it is freed. */
+	new_bp->b_pag = pag;
+	spin_unlock(&pag->pag_buf_lock);
+	*bpp = new_bp;
+	return 0;
+
+out_free_buf:
+	xfs_buf_free(new_bp);
+out_drop_pag:
+	xfs_perag_put(pag);
+	return error;
+}
+
+/*
+ * 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.
+ */
+int
+xfs_buf_get_map(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_perag	*pag;
+	struct xfs_buf		*bp = NULL;
+	struct xfs_buf_map	cmap = { .bm_bn = map[0].bm_bn };
+	int			error;
+	int			i;
+
+	if (flags & XBF_LIVESCAN)
+		cmap.bm_flags |= XBM_LIVESCAN;
+	for (i = 0; i < nmaps; i++)
+		cmap.bm_len += map[i].bm_len;
+
+	error = xfs_buf_map_verify(btp, &cmap);
+	if (error)
+		return error;
+
+	pag = xfs_perag_get(btp->bt_mount,
+			    xfs_daddr_to_agno(btp->bt_mount, cmap.bm_bn));
+
+	error = xfs_buf_lookup(pag, &cmap, flags, &bp);
+	if (error && error != -ENOENT)
+		goto out_put_perag;
+
+	/* cache hits always outnumber misses by at least 10:1 */
+	if (unlikely(!bp)) {
+		XFS_STATS_INC(btp->bt_mount, xb_miss_locked);
+
+		if (flags & XBF_INCORE)
+			goto out_put_perag;
+
+		/* xfs_buf_find_insert() consumes the perag reference. */
+		error = xfs_buf_find_insert(btp, pag, &cmap, map, nmaps,
+				flags, &bp);
+		if (error)
+			return error;
+	} else {
+		XFS_STATS_INC(btp->bt_mount, xb_get_locked);
+		xfs_perag_put(pag);
+	}
+
+	/* We do not hold a perag reference anymore. */
+	if (!bp->b_addr) {
+		error = _xfs_buf_map_pages(bp, flags);
+		if (unlikely(error)) {
+			xfs_warn_ratelimited(btp->bt_mount,
+				"%s: failed to map %u pages", __func__,
+				bp->b_page_count);
+			xfs_buf_relse(bp);
+			return error;
+		}
+	}
+
+	/*
+	 * 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(btp->bt_mount, xb_get);
+	trace_xfs_buf_get(bp, flags, _RET_IP_);
+	*bpp = bp;
+	return 0;
+
+out_put_perag:
+	xfs_perag_put(pag);
+	return error;
+}
+
+int
+_xfs_buf_read(
+	struct xfs_buf		*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 | XBF_DONE);
+	bp->b_flags |= flags & (XBF_READ | XBF_ASYNC | XBF_READ_AHEAD);
+
+	return xfs_buf_submit(bp);
+}
+
+/*
+ * Reverify a buffer found in cache without an attached ->b_ops.
+ *
+ * If the caller passed an ops structure and the buffer doesn't have ops
+ * assigned, set the ops and use it to verify the contents. If verification
+ * fails, clear XBF_DONE. We assume the buffer has no recorded errors and is
+ * already in XBF_DONE state on entry.
+ *
+ * Under normal operations, every in-core buffer is verified on read I/O
+ * completion. There are two scenarios that can lead to in-core buffers without
+ * an assigned ->b_ops. The first is during log recovery of buffers on a V4
+ * filesystem, though these buffers are purged at the end of recovery. The
+ * other is online repair, which intentionally reads with a NULL buffer ops to
+ * run several verifiers across an in-core buffer in order to establish buffer
+ * type.  If repair can't establish that, the buffer will be left in memory
+ * with NULL buffer ops.
+ */
+int
+xfs_buf_reverify(
+	struct xfs_buf		*bp,
+	const struct xfs_buf_ops *ops)
+{
+	ASSERT(bp->b_flags & XBF_DONE);
+	ASSERT(bp->b_error == 0);
+
+	if (!ops || bp->b_ops)
+		return 0;
+
+	bp->b_ops = ops;
+	bp->b_ops->verify_read(bp);
+	if (bp->b_error)
+		bp->b_flags &= ~XBF_DONE;
+	return bp->b_error;
+}
+
+int
+xfs_buf_read_map(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp,
+	const struct xfs_buf_ops *ops,
+	xfs_failaddr_t		fa)
+{
+	struct xfs_buf		*bp;
+	int			error;
+
+	flags |= XBF_READ;
+	*bpp = NULL;
+
+	error = xfs_buf_get_map(target, map, nmaps, flags, &bp);
+	if (error)
+		return error;
+
+	trace_xfs_buf_read(bp, flags, _RET_IP_);
+
+	if (!(bp->b_flags & XBF_DONE)) {
+		/* Initiate the buffer read and wait. */
+		XFS_STATS_INC(target->bt_mount, xb_get_read);
+		bp->b_ops = ops;
+		error = _xfs_buf_read(bp, flags);
+
+		/* Readahead iodone already dropped the buffer, so exit. */
+		if (flags & XBF_ASYNC)
+			return 0;
+	} else {
+		/* Buffer already read; all we need to do is check it. */
+		error = xfs_buf_reverify(bp, ops);
+
+		/* Readahead already finished; drop the buffer and exit. */
+		if (flags & XBF_ASYNC) {
+			xfs_buf_relse(bp);
+			return 0;
+		}
+
+		/* We do not want read in the flags */
+		bp->b_flags &= ~XBF_READ;
+		ASSERT(bp->b_ops != NULL || ops == NULL);
+	}
+
+	/*
+	 * If we've had a read error, then the contents of the buffer are
+	 * invalid and should not be used. To ensure that a followup read tries
+	 * to pull the buffer from disk again, we clear the XBF_DONE flag and
+	 * mark the buffer stale. This ensures that anyone who has a current
+	 * reference to the buffer will interpret it's contents correctly and
+	 * future cache lookups will also treat it as an empty, uninitialised
+	 * buffer.
+	 */
+	if (error) {
+		/*
+		 * Check against log shutdown for error reporting because
+		 * metadata writeback may require a read first and we need to
+		 * report errors in metadata writeback until the log is shut
+		 * down. High level transaction read functions already check
+		 * against mount shutdown, anyway, so we only need to be
+		 * concerned about low level IO interactions here.
+		 */
+		if (!xlog_is_shutdown(target->bt_mount->m_log))
+			xfs_buf_ioerror_alert(bp, fa);
+
+		bp->b_flags &= ~XBF_DONE;
+		xfs_buf_stale(bp);
+		xfs_buf_relse(bp);
+
+		/* bad CRC means corrupted metadata */
+		if (error == -EFSBADCRC)
+			error = -EFSCORRUPTED;
+		return error;
+	}
+
+	*bpp = bp;
+	return 0;
+}
+
+/*
+ *	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)
+{
+	struct xfs_buf		*bp;
+
+	xfs_buf_read_map(target, map, nmaps,
+		     XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD, &bp, ops,
+		     __this_address);
+}
+
+/*
+ * Read an uncached buffer from disk. Allocates and returns a locked
+ * buffer containing the disk contents or nothing. Uncached buffers always have
+ * a cache index of XFS_BUF_DADDR_NULL so we can easily determine if the buffer
+ * is cached or uncached during fault diagnosis.
+ */
+int
+xfs_buf_read_uncached(
+	struct xfs_buftarg	*target,
+	xfs_daddr_t		daddr,
+	size_t			numblks,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp,
+	const struct xfs_buf_ops *ops)
+{
+	struct xfs_buf		*bp;
+	int			error;
+
+	*bpp = NULL;
+
+	error = xfs_buf_get_uncached(target, numblks, flags, &bp);
+	if (error)
+		return error;
+
+	/* set up the buffer for a read IO */
+	ASSERT(bp->b_map_count == 1);
+	bp->b_rhash_key = XFS_BUF_DADDR_NULL;
+	bp->b_maps[0].bm_bn = daddr;
+	bp->b_flags |= XBF_READ;
+	bp->b_ops = ops;
+
+	xfs_buf_submit(bp);
+	if (bp->b_error) {
+		error = bp->b_error;
+		xfs_buf_relse(bp);
+		return error;
+	}
+
+	*bpp = bp;
+	return 0;
+}
+
+int
+xfs_buf_get_uncached(
+	struct xfs_buftarg	*target,
+	size_t			numblks,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	int			error;
+	struct xfs_buf		*bp;
+	DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
+
+	*bpp = NULL;
+
+	/* flags might contain irrelevant bits, pass only what we care about */
+	error = _xfs_buf_alloc(target, &map, 1, flags & XBF_NO_IOACCT, &bp);
+	if (error)
+		return error;
+
+	error = xfs_buf_alloc_pages(bp, flags);
+	if (error)
+		goto fail_free_buf;
+
+	error = _xfs_buf_map_pages(bp, 0);
+	if (unlikely(error)) {
+		xfs_warn(target->bt_mount,
+			"%s: failed to map pages", __func__);
+		goto fail_free_buf;
+	}
+
+	trace_xfs_buf_get_uncached(bp, _RET_IP_);
+	*bpp = bp;
+	return 0;
+
+fail_free_buf:
+	xfs_buf_free(bp);
+	return error;
+}
+
+/*
+ *	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(
+	struct xfs_buf		*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(
+	struct xfs_buf		*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_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(
+	struct xfs_buf		*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);
+}
+
+static void
+xfs_buf_ioerror_alert_ratelimited(
+	struct xfs_buf		*bp)
+{
+	static unsigned long	lasttime;
+	static struct xfs_buftarg *lasttarg;
+
+	if (bp->b_target != lasttarg ||
+	    time_after(jiffies, (lasttime + 5*HZ))) {
+		lasttime = jiffies;
+		xfs_buf_ioerror_alert(bp, __this_address);
+	}
+	lasttarg = bp->b_target;
+}
+
+/*
+ * Account for this latest trip around the retry handler, and decide if
+ * we've failed enough times to constitute a permanent failure.
+ */
+static bool
+xfs_buf_ioerror_permanent(
+	struct xfs_buf		*bp,
+	struct xfs_error_cfg	*cfg)
+{
+	struct xfs_mount	*mp = bp->b_mount;
+
+	if (cfg->max_retries != XFS_ERR_RETRY_FOREVER &&
+	    ++bp->b_retries > cfg->max_retries)
+		return true;
+	if (cfg->retry_timeout != XFS_ERR_RETRY_FOREVER &&
+	    time_after(jiffies, cfg->retry_timeout + bp->b_first_retry_time))
+		return true;
+
+	/* At unmount we may treat errors differently */
+	if (xfs_is_unmounting(mp) && mp->m_fail_unmount)
+		return true;
+
+	return false;
+}
+
+/*
+ * On a sync write or shutdown we just want to stale the buffer and let the
+ * caller handle the error in bp->b_error appropriately.
+ *
+ * If the write was asynchronous then no one will be looking for the error.  If
+ * this is the first failure of this type, clear the error state and write the
+ * buffer out again. This means we always retry an async write failure at least
+ * once, but we also need to set the buffer up to behave correctly now for
+ * repeated failures.
+ *
+ * If we get repeated async write failures, then we take action according to the
+ * error configuration we have been set up to use.
+ *
+ * Returns true if this function took care of error handling and the caller must
+ * not touch the buffer again.  Return false if the caller should proceed with
+ * normal I/O completion handling.
+ */
+static bool
+xfs_buf_ioend_handle_error(
+	struct xfs_buf		*bp)
+{
+	struct xfs_mount	*mp = bp->b_mount;
+	struct xfs_error_cfg	*cfg;
+
+	/*
+	 * If we've already shutdown the journal because of I/O errors, there's
+	 * no point in giving this a retry.
+	 */
+	if (xlog_is_shutdown(mp->m_log))
+		goto out_stale;
+
+	xfs_buf_ioerror_alert_ratelimited(bp);
+
+	/*
+	 * We're not going to bother about retrying this during recovery.
+	 * One strike!
+	 */
+	if (bp->b_flags & _XBF_LOGRECOVERY) {
+		xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
+		return false;
+	}
+
+	/*
+	 * Synchronous writes will have callers process the error.
+	 */
+	if (!(bp->b_flags & XBF_ASYNC))
+		goto out_stale;
+
+	trace_xfs_buf_iodone_async(bp, _RET_IP_);
+
+	cfg = xfs_error_get_cfg(mp, XFS_ERR_METADATA, bp->b_error);
+	if (bp->b_last_error != bp->b_error ||
+	    !(bp->b_flags & (XBF_STALE | XBF_WRITE_FAIL))) {
+		bp->b_last_error = bp->b_error;
+		if (cfg->retry_timeout != XFS_ERR_RETRY_FOREVER &&
+		    !bp->b_first_retry_time)
+			bp->b_first_retry_time = jiffies;
+		goto resubmit;
+	}
+
+	/*
+	 * Permanent error - we need to trigger a shutdown if we haven't already
+	 * to indicate that inconsistency will result from this action.
+	 */
+	if (xfs_buf_ioerror_permanent(bp, cfg)) {
+		xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
+		goto out_stale;
+	}
+
+	/* Still considered a transient error. Caller will schedule retries. */
+	if (bp->b_flags & _XBF_INODES)
+		xfs_buf_inode_io_fail(bp);
+	else if (bp->b_flags & _XBF_DQUOTS)
+		xfs_buf_dquot_io_fail(bp);
+	else
+		ASSERT(list_empty(&bp->b_li_list));
+	xfs_buf_ioerror(bp, 0);
+	xfs_buf_relse(bp);
+	return true;
+
+resubmit:
+	xfs_buf_ioerror(bp, 0);
+	bp->b_flags |= (XBF_DONE | XBF_WRITE_FAIL);
+	xfs_buf_submit(bp);
+	return true;
+out_stale:
+	xfs_buf_stale(bp);
+	bp->b_flags |= XBF_DONE;
+	bp->b_flags &= ~XBF_WRITE;
+	trace_xfs_buf_error_relse(bp, _RET_IP_);
+	return false;
+}
+
+static void
+xfs_buf_ioend(
+	struct xfs_buf	*bp)
+{
+	trace_xfs_buf_iodone(bp, _RET_IP_);
+
+	/*
+	 * 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);
+
+	if (bp->b_flags & XBF_READ) {
+		if (!bp->b_error && bp->b_ops)
+			bp->b_ops->verify_read(bp);
+		if (!bp->b_error)
+			bp->b_flags |= XBF_DONE;
+	} else {
+		if (!bp->b_error) {
+			bp->b_flags &= ~XBF_WRITE_FAIL;
+			bp->b_flags |= XBF_DONE;
+		}
+
+		if (unlikely(bp->b_error) && xfs_buf_ioend_handle_error(bp))
+			return;
+
+		/* clear the retry state */
+		bp->b_last_error = 0;
+		bp->b_retries = 0;
+		bp->b_first_retry_time = 0;
+
+		/*
+		 * Note that for things like remote attribute buffers, there may
+		 * not be a buffer log item here, so processing the buffer log
+		 * item must remain optional.
+		 */
+		if (bp->b_log_item)
+			xfs_buf_item_done(bp);
+
+		if (bp->b_flags & _XBF_INODES)
+			xfs_buf_inode_iodone(bp);
+		else if (bp->b_flags & _XBF_DQUOTS)
+			xfs_buf_dquot_iodone(bp);
+
+	}
+
+	bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD |
+			 _XBF_LOGRECOVERY);
+
+	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, struct xfs_buf, 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_mount->m_buf_workqueue, &bp->b_ioend_work);
+}
+
+void
+__xfs_buf_ioerror(
+	struct xfs_buf		*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,
+	xfs_failaddr_t		func)
+{
+	xfs_buf_alert_ratelimited(bp, "XFS: metadata IO error",
+		"metadata I/O error in \"%pS\" at daddr 0x%llx len %d error %d",
+				  func, (uint64_t)xfs_buf_daddr(bp),
+				  bp->b_length, -bp->b_error);
+}
+
+/*
+ * To simulate an I/O failure, the buffer must be locked and held with at least
+ * three references. The LRU reference is dropped by the stale call. The buf
+ * item reference is dropped via ioend processing. The third reference is owned
+ * by the caller and is dropped on I/O completion if the buffer is XBF_ASYNC.
+ */
+void
+xfs_buf_ioend_fail(
+	struct xfs_buf	*bp)
+{
+	bp->b_flags &= ~XBF_DONE;
+	xfs_buf_stale(bp);
+	xfs_buf_ioerror(bp, -EIO);
+	xfs_buf_ioend(bp);
+}
+
+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_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;
+
+	if (!bio->bi_status &&
+	    (bp->b_flags & XBF_WRITE) && (bp->b_flags & XBF_ASYNC) &&
+	    XFS_TEST_ERROR(false, bp->b_mount, XFS_ERRTAG_BUF_IOERROR))
+		bio->bi_status = BLK_STS_IOERR;
+
+	/*
+	 * 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,
+	blk_opf_t	op)
+{
+	int		page_index;
+	unsigned 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 = bio_max_segs(total_nr_pages);
+
+	bio = bio_alloc(bp->b_target->bt_bdev, nr_pages, op, GFP_NOIO);
+	bio->bi_iter.bi_sector = sector;
+	bio->bi_end_io = xfs_buf_bio_end_io;
+	bio->bi_private = bp;
+
+	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;
+	blk_opf_t	op;
+	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;
+
+	if (bp->b_flags & XBF_WRITE) {
+		op = REQ_OP_WRITE;
+
+		/*
+		 * 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_mount,
+						   SHUTDOWN_CORRUPT_INCORE);
+				return;
+			}
+		} else if (bp->b_rhash_key != XFS_BUF_DADDR_NULL) {
+			struct xfs_mount *mp = bp->b_mount;
+
+			/*
+			 * non-crc filesystems don't attach verifiers during
+			 * log recovery, so don't warn for such filesystems.
+			 */
+			if (xfs_has_crc(mp)) {
+				xfs_warn(mp,
+					"%s: no buf ops on daddr 0x%llx len %d",
+					__func__, xfs_buf_daddr(bp),
+					bp->b_length);
+				xfs_hex_dump(bp->b_addr,
+						XFS_CORRUPTION_DUMP_LEN);
+				dump_stack();
+			}
+		}
+	} else {
+		op = REQ_OP_READ;
+		if (bp->b_flags & XBF_READ_AHEAD)
+			op |= REQ_RAHEAD;
+	}
+
+	/* we only use the buffer cache for meta-data */
+	op |= 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_length);
+	blk_start_plug(&plug);
+	for (i = 0; i < bp->b_map_count; i++) {
+		xfs_buf_ioapply_map(bp, i, &offset, &size, op);
+		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.
+ */
+static 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 log shutdown we stale and complete the buffer immediately. We can
+	 * be called to read the superblock before the log has been set up, so
+	 * be careful checking the log state.
+	 *
+	 * Checking the mount shutdown state here can result in the log tail
+	 * moving inappropriately on disk as the log may not yet be shut down.
+	 * i.e. failing this buffer on mount shutdown can remove it from the AIL
+	 * and move the tail of the log forwards without having written this
+	 * buffer to disk. This corrupts the log tail state in memory, and
+	 * because the log may not be shut down yet, it can then be propagated
+	 * to disk before the log is shutdown. Hence we check log shutdown
+	 * state here rather than mount state to avoid corrupting the log tail
+	 * on shutdown.
+	 */
+	if (bp->b_mount->m_log &&
+	    xlog_is_shutdown(bp->b_mount->m_log)) {
+		xfs_buf_ioend_fail(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;
+
+	page = bp->b_pages[offset >> PAGE_SHIFT];
+	return page_address(page) + (offset & (PAGE_SIZE-1));
+}
+
+void
+xfs_buf_zero(
+	struct xfs_buf		*bp,
+	size_t			boff,
+	size_t			bsize)
+{
+	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_length) - boff);
+
+		ASSERT((csize + page_offset) <= PAGE_SIZE);
+
+		memset(page_address(page) + page_offset, 0, csize);
+
+		boff += csize;
+	}
+}
+
+/*
+ * Log a message about and stale a buffer that a caller has decided is corrupt.
+ *
+ * This function should be called for the kinds of metadata corruption that
+ * cannot be detect from a verifier, such as incorrect inter-block relationship
+ * data.  Do /not/ call this function from a verifier function.
+ *
+ * The buffer must be XBF_DONE prior to the call.  Afterwards, the buffer will
+ * be marked stale, but b_error will not be set.  The caller is responsible for
+ * releasing the buffer or fixing it.
+ */
+void
+__xfs_buf_mark_corrupt(
+	struct xfs_buf		*bp,
+	xfs_failaddr_t		fa)
+{
+	ASSERT(bp->b_flags & XBF_DONE);
+
+	xfs_buf_corruption_error(bp, fa);
+	xfs_buf_stale(bp);
+}
+
+/*
+ *	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_drain_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_drain_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;
+}
+
+/*
+ * Wait for outstanding I/O on the buftarg to complete.
+ */
+void
+xfs_buftarg_wait(
+	struct xfs_buftarg	*btp)
+{
+	/*
+	 * 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);
+}
+
+void
+xfs_buftarg_drain(
+	struct xfs_buftarg	*btp)
+{
+	LIST_HEAD(dispose);
+	int			loop = 0;
+	bool			write_fail = false;
+
+	xfs_buftarg_wait(btp);
+
+	/* 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_drain_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) {
+				write_fail = true;
+				xfs_buf_alert_ratelimited(bp,
+					"XFS: Corruption Alert",
+"Corruption Alert: Buffer at daddr 0x%llx had permanent write failures!",
+					(long long)xfs_buf_daddr(bp));
+			}
+			xfs_buf_rele(bp);
+		}
+		if (loop++ != 0)
+			delay(100);
+	}
+
+	/*
+	 * If one or more failed buffers were freed, that means dirty metadata
+	 * was thrown away. This should only ever happen after I/O completion
+	 * handling has elevated I/O error(s) to permanent failures and shuts
+	 * down the journal.
+	 */
+	if (write_fail) {
+		ASSERT(xlog_is_shutdown(btp->bt_mount->m_log));
+		xfs_alert(btp->bt_mount,
+	      "Please run xfs_repair to determine the extent of the problem.");
+	}
+}
+
+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)
+{
+	struct block_device	*bdev = btp->bt_bdev;
+
+	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);
+
+	fs_put_dax(btp->bt_daxdev, btp->bt_mount);
+	/* the main block device is closed by kill_block_super */
+	if (bdev != btp->bt_mount->m_super->s_bdev)
+		blkdev_put(bdev, btp->bt_mount->m_super);
+
+	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));
+}
+
+struct xfs_buftarg *
+xfs_alloc_buftarg(
+	struct xfs_mount	*mp,
+	struct block_device	*bdev)
+{
+	xfs_buftarg_t		*btp;
+	const struct dax_holder_operations *ops = NULL;
+
+#if defined(CONFIG_FS_DAX) && defined(CONFIG_MEMORY_FAILURE)
+	ops = &xfs_dax_holder_operations;
+#endif
+	btp = kmem_zalloc(sizeof(*btp), KM_NOFS);
+
+	btp->bt_mount = mp;
+	btp->bt_dev =  bdev->bd_dev;
+	btp->bt_bdev = bdev;
+	btp->bt_daxdev = fs_dax_get_by_bdev(bdev, &btp->bt_dax_part_off,
+					    mp, ops);
+
+	/*
+	 * Buffer IO error rate limiting. Limit it to no more than 10 messages
+	 * per 30 seconds so as to not spam logs too much on repeated errors.
+	 */
+	ratelimit_state_init(&btp->bt_ioerror_rl, 30 * HZ,
+			     DEFAULT_RATELIMIT_BURST);
+
+	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, "xfs-buf:%s",
+			      mp->m_super->s_id))
+		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,
+	const struct list_head	*a,
+	const 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;
+	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_trylock(bp))
+				continue;
+			if (xfs_buf_ispinned(bp)) {
+				xfs_buf_unlock(bp);
+				pinned++;
+				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;
+}
+
+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_mount, XFS_ERRTAG_BUF_LRU_REF))
+		lru_ref = 0;
+
+	atomic_set(&bp->b_lru_ref, lru_ref);
+}
+
+/*
+ * Verify an on-disk magic value against the magic value specified in the
+ * verifier structure. The verifier magic is in disk byte order so the caller is
+ * expected to pass the value directly from disk.
+ */
+bool
+xfs_verify_magic(
+	struct xfs_buf		*bp,
+	__be32			dmagic)
+{
+	struct xfs_mount	*mp = bp->b_mount;
+	int			idx;
+
+	idx = xfs_has_crc(mp);
+	if (WARN_ON(!bp->b_ops || !bp->b_ops->magic[idx]))
+		return false;
+	return dmagic == bp->b_ops->magic[idx];
+}
+/*
+ * Verify an on-disk magic value against the magic value specified in the
+ * verifier structure. The verifier magic is in disk byte order so the caller is
+ * expected to pass the value directly from disk.
+ */
+bool
+xfs_verify_magic16(
+	struct xfs_buf		*bp,
+	__be16			dmagic)
+{
+	struct xfs_mount	*mp = bp->b_mount;
+	int			idx;
+
+	idx = xfs_has_crc(mp);
+	if (WARN_ON(!bp->b_ops || !bp->b_ops->magic16[idx]))
+		return false;
+	return dmagic == bp->b_ops->magic16[idx];
+}