// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2000-2006 Silicon Graphics, Inc.
 * All Rights Reserved.
 */
#include "xfs_platform.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"
#include "xfs_buf_mem.h"
#include "xfs_notify_failure.h"

struct kmem_cache *xfs_buf_cache;

/*
 * Locking orders
 *
 * xfs_buf_stale:
 *      b_sema (caller holds)
 *        b_lock
 *          lru_lock
 *
 * xfs_buf_rele:
 *      b_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 void xfs_buf_submit(struct xfs_buf *bp);
static int xfs_buf_iowait(struct xfs_buf *bp);

static inline bool xfs_buf_is_uncached(struct xfs_buf *bp)
{
        return bp->b_rhash_key == XFS_BUF_DADDR_NULL;
}

/*
 * 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;

        spin_lock(&bp->b_lock);
        atomic_set(&bp->b_lru_ref, 0);
        if (!(bp->b_state & XFS_BSTATE_DISPOSE) &&
            (list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru)))
                bp->b_hold--;

        ASSERT(bp->b_hold >= 1);
        spin_unlock(&bp->b_lock);
}

static void
xfs_buf_free_callback(
        struct callback_head    *cb)
{
        struct xfs_buf          *bp = container_of(cb, struct xfs_buf, b_rcu);

        if (bp->b_maps != &bp->__b_map)
                kfree(bp->b_maps);
        kmem_cache_free(xfs_buf_cache, bp);
}

static void
xfs_buf_free(
        struct xfs_buf          *bp)
{
        unsigned int            size = BBTOB(bp->b_length);

        might_sleep();
        trace_xfs_buf_free(bp, _RET_IP_);

        ASSERT(list_empty(&bp->b_lru));

        if (!xfs_buftarg_is_mem(bp->b_target) && size >= PAGE_SIZE)
                mm_account_reclaimed_pages(howmany(size, PAGE_SHIFT));

        if (is_vmalloc_addr(bp->b_addr))
                vfree(bp->b_addr);
        else if (bp->b_flags & _XBF_KMEM)
                kfree(bp->b_addr);
        else
                folio_put(virt_to_folio(bp->b_addr));

        call_rcu(&bp->b_rcu, xfs_buf_free_callback);
}

static int
xfs_buf_alloc_kmem(
        struct xfs_buf          *bp,
        size_t                  size,
        gfp_t                   gfp_mask)
{
        ASSERT(is_power_of_2(size));
        ASSERT(size < PAGE_SIZE);

        bp->b_addr = kmalloc(size, gfp_mask | __GFP_NOFAIL);
        if (!bp->b_addr)
                return -ENOMEM;

        /*
         * Slab guarantees that we get back naturally aligned allocations for
         * power of two sizes.  Keep this check as the canary in the coal mine
         * if anything changes in slab.
         */
        if (WARN_ON_ONCE(!IS_ALIGNED((unsigned long)bp->b_addr, size))) {
                kfree(bp->b_addr);
                bp->b_addr = NULL;
                return -ENOMEM;
        }
        bp->b_flags |= _XBF_KMEM;
        trace_xfs_buf_backing_kmem(bp, _RET_IP_);
        return 0;
}

/*
 * Allocate backing memory for a buffer.
 *
 * For tmpfs-backed buffers used by in-memory btrees this directly maps the
 * tmpfs page cache folios.
 *
 * For real file system buffers there are three different kinds backing memory:
 *
 * The first type backs the buffer by a kmalloc allocation.  This is done for
 * less than PAGE_SIZE allocations to avoid wasting memory.
 *
 * The second type is a single folio buffer - this may be a high order folio or
 * just a single page sized folio, but either way they get treated the same way
 * by the rest of the code - the buffer memory spans a single contiguous memory
 * region that we don't have to map and unmap to access the data directly.
 *
 * The third type of buffer is the vmalloc()d buffer. This provides the buffer
 * with the required contiguous memory region but backed by discontiguous
 * physical pages.
 */
static int
xfs_buf_alloc_backing_mem(
        struct xfs_buf  *bp,
        xfs_buf_flags_t flags)
{
        size_t          size = BBTOB(bp->b_length);
        gfp_t           gfp_mask = GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOWARN;
        struct folio    *folio;

        if (xfs_buftarg_is_mem(bp->b_target))
                return xmbuf_map_backing_mem(bp);

        /* Assure zeroed buffer for non-read cases. */
        if (!(flags & XBF_READ))
                gfp_mask |= __GFP_ZERO;

        if (flags & XBF_READ_AHEAD)
                gfp_mask |= __GFP_NORETRY;

        /*
         * For buffers smaller than PAGE_SIZE use a kmalloc allocation if that
         * is properly aligned.  The slab allocator now guarantees an aligned
         * allocation for all power of two sizes, which matches most of the
         * smaller than PAGE_SIZE buffers used by XFS.
         */
        if (size < PAGE_SIZE && is_power_of_2(size))
                return xfs_buf_alloc_kmem(bp, size, gfp_mask);

        /*
         * Don't bother with the retry loop for single PAGE allocations: vmalloc
         * won't do any better.
         */
        if (size <= PAGE_SIZE)
                gfp_mask |= __GFP_NOFAIL;

        /*
         * Optimistically attempt a single high order folio allocation for
         * larger than PAGE_SIZE buffers.
         *
         * Allocating a high order folio makes the assumption that buffers are a
         * power-of-2 size, matching the power-of-2 folios sizes available.
         *
         * The exception here are user xattr data buffers, which can be arbitrarily
         * sized up to 64kB plus structure metadata, skip straight to the vmalloc
         * path for them instead of wasting memory here.
         */
        if (size > PAGE_SIZE) {
                if (!is_power_of_2(size))
                        goto fallback;
                gfp_mask &= ~__GFP_DIRECT_RECLAIM;
                gfp_mask |= __GFP_NORETRY;
        }
        folio = folio_alloc(gfp_mask, get_order(size));
        if (!folio) {
                if (size <= PAGE_SIZE)
                        return -ENOMEM;
                trace_xfs_buf_backing_fallback(bp, _RET_IP_);
                goto fallback;
        }
        bp->b_addr = folio_address(folio);
        trace_xfs_buf_backing_folio(bp, _RET_IP_);
        return 0;

fallback:
        for (;;) {
                bp->b_addr = __vmalloc(size, gfp_mask);
                if (bp->b_addr)
                        break;
                if (flags & XBF_READ_AHEAD)
                        return -ENOMEM;
                XFS_STATS_INC(bp->b_mount, xb_page_retries);
                memalloc_retry_wait(gfp_mask);
        }

        trace_xfs_buf_backing_vmalloc(bp, _RET_IP_);
        return 0;
}

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_KERNEL | __GFP_NOLOCKDEP | __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_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD);

        /*
         * A new buffer is held and locked by the owner.  This ensures that the
         * buffer is owned by the caller and racing RCU lookups right after
         * inserting into the hash table are safe (and will have to wait for
         * the unlock to do anything non-trivial).
         */
        bp->b_hold = 1;
        sema_init(&bp->b_sema, 0); /* held, no waiters */

        spin_lock_init(&bp->b_lock);
        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);
        bp->b_target = target;
        bp->b_mount = target->bt_mount;
        bp->b_flags = flags;
        bp->b_rhash_key = map[0].bm_bn;
        bp->b_length = 0;
        bp->b_map_count = nmaps;
        if (nmaps == 1)
                bp->b_maps = &bp->__b_map;
        else
                bp->b_maps = kzalloc_objs(struct xfs_buf_map, nmaps,
                                          GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOFAIL);
        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_);

        error = xfs_buf_alloc_backing_mem(bp, flags);
        if (error) {
                xfs_buf_free(bp);
                return error;
        }

        *bpp = bp;
        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.
                 *
                 * Note: If we're scanning for incore buffers to stale, don't
                 * complain if we find non-stale buffers.
                 */
                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_cache_init(
        struct xfs_buf_cache    *bch)
{
        return rhashtable_init(&bch->bc_hash, &xfs_buf_hash_params);
}

void
xfs_buf_cache_destroy(
        struct xfs_buf_cache    *bch)
{
        rhashtable_destroy(&bch->bc_hash);
}

static int
xfs_buf_map_verify(
        struct xfs_buftarg      *btp,
        struct xfs_buf_map      *map)
{
        /* 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.
         */
        if (map->bm_bn < 0 || map->bm_bn >= btp->bt_nr_sectors) {
                xfs_alert(btp->bt_mount,
                          "%s: daddr 0x%llx out of range, EOFS 0x%llx",
                          __func__, map->bm_bn, btp->bt_nr_sectors);
                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;
                bp->b_ops = NULL;
        }
        return 0;
}

static bool
xfs_buf_try_hold(
        struct xfs_buf          *bp)
{
        spin_lock(&bp->b_lock);
        if (bp->b_hold == 0) {
                spin_unlock(&bp->b_lock);
                return false;
        }
        bp->b_hold++;
        spin_unlock(&bp->b_lock);
        return true;
}

static inline int
xfs_buf_lookup(
        struct xfs_buf_cache    *bch,
        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(&bch->bc_hash, map, xfs_buf_hash_params);
        if (!bp || !xfs_buf_try_hold(bp)) {
                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_buf_cache    *bch,
        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;

        /* The new buffer keeps the perag reference until it is freed. */
        new_bp->b_pag = pag;

        rcu_read_lock();
        bp = rhashtable_lookup_get_insert_fast(&bch->bc_hash,
                        &new_bp->b_rhash_head, xfs_buf_hash_params);
        if (IS_ERR(bp)) {
                rcu_read_unlock();
                error = PTR_ERR(bp);
                goto out_free_buf;
        }
        if (bp && xfs_buf_try_hold(bp)) {
                /* found an existing buffer */
                rcu_read_unlock();
                error = xfs_buf_find_lock(bp, flags);
                if (error)
                        xfs_buf_rele(bp);
                else
                        *bpp = bp;
                goto out_free_buf;
        }
        rcu_read_unlock();

        *bpp = new_bp;
        return 0;

out_free_buf:
        xfs_buf_free(new_bp);
out_drop_pag:
        if (pag)
                xfs_perag_put(pag);
        return error;
}

static inline struct xfs_perag *
xfs_buftarg_get_pag(
        struct xfs_buftarg              *btp,
        const struct xfs_buf_map        *map)
{
        struct xfs_mount                *mp = btp->bt_mount;

        if (xfs_buftarg_is_mem(btp))
                return NULL;
        return xfs_perag_get(mp, xfs_daddr_to_agno(mp, map->bm_bn));
}

static inline struct xfs_buf_cache *
xfs_buftarg_buf_cache(
        struct xfs_buftarg              *btp,
        struct xfs_perag                *pag)
{
        if (pag)
                return &pag->pag_bcache;
        return btp->bt_cache;
}

/*
 * 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_buf_cache    *bch;
        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_buftarg_get_pag(btp, &cmap);
        bch = xfs_buftarg_buf_cache(btp, pag);

        error = xfs_buf_lookup(bch, &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, bch, pag, &cmap, map, nmaps,
                                flags, &bp);
                if (error)
                        return error;
        } else {
                XFS_STATS_INC(btp->bt_mount, xb_get_locked);
                if (pag)
                        xfs_perag_put(pag);
        }

        /*
         * 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:
        if (pag)
                xfs_perag_put(pag);
        return error;
}

int
_xfs_buf_read(
        struct xfs_buf          *bp)
{
        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 |= XBF_READ;
        xfs_buf_submit(bp);
        return xfs_buf_iowait(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;

        ASSERT(!(flags & (XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD)));

        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);
        } else {
                /* Buffer already read; all we need to do is check it. */
                error = xfs_buf_reverify(bp, ops);

                /* 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)
{
        const xfs_buf_flags_t   flags = XBF_READ | XBF_ASYNC | XBF_READ_AHEAD;
        struct xfs_buf          *bp;

        /*
         * Currently we don't have a good means or justification for performing
         * xmbuf_map_page asynchronously, so we don't do readahead.
         */
        if (xfs_buftarg_is_mem(target))
                return;

        if (xfs_buf_get_map(target, map, nmaps, flags | XBF_TRYLOCK, &bp))
                return;
        trace_xfs_buf_readahead(bp, 0, _RET_IP_);

        if (bp->b_flags & XBF_DONE) {
                xfs_buf_reverify(bp, ops);
                xfs_buf_relse(bp);
                return;
        }
        XFS_STATS_INC(target->bt_mount, xb_get_read);
        bp->b_ops = ops;
        bp->b_flags &= ~(XBF_WRITE | XBF_DONE);
        bp->b_flags |= flags;
        percpu_counter_inc(&target->bt_readahead_count);
        xfs_buf_submit(bp);
}

/*
 * 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,
        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, &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);
        error = xfs_buf_iowait(bp);
        if (error) {
                xfs_buf_relse(bp);
                return error;
        }

        *bpp = bp;
        return 0;
}

int
xfs_buf_get_uncached(
        struct xfs_buftarg      *target,
        size_t                  numblks,
        struct xfs_buf          **bpp)
{
        int                     error;
        DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);

        error = xfs_buf_alloc(target, &map, 1, 0, bpp);
        if (!error)
                trace_xfs_buf_get_uncached(*bpp, _RET_IP_);
        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_);

        spin_lock(&bp->b_lock);
        bp->b_hold++;
        spin_unlock(&bp->b_lock);
}

static void
xfs_buf_rele_uncached(
        struct xfs_buf          *bp)
{
        ASSERT(list_empty(&bp->b_lru));

        spin_lock(&bp->b_lock);
        if (--bp->b_hold) {
                spin_unlock(&bp->b_lock);
                return;
        }
        spin_unlock(&bp->b_lock);
        xfs_buf_free(bp);
}

static void
xfs_buf_rele_cached(
        struct xfs_buf          *bp)
{
        struct xfs_buftarg      *btp = bp->b_target;
        struct xfs_perag        *pag = bp->b_pag;
        struct xfs_buf_cache    *bch = xfs_buftarg_buf_cache(btp, pag);
        bool                    freebuf = false;

        trace_xfs_buf_rele(bp, _RET_IP_);

        spin_lock(&bp->b_lock);
        ASSERT(bp->b_hold >= 1);
        if (bp->b_hold > 1) {
                bp->b_hold--;
                goto out_unlock;
        }

        /* we are asked to drop the last reference */
        if (atomic_read(&bp->b_lru_ref)) {
                /*
                 * If the buffer is added to the LRU, keep the reference to the
                 * buffer for the LRU and clear the (now stale) dispose list
                 * state flag, else drop the reference.
                 */
                if (list_lru_add_obj(&btp->bt_lru, &bp->b_lru))
                        bp->b_state &= ~XFS_BSTATE_DISPOSE;
                else
                        bp->b_hold--;
        } else {
                bp->b_hold--;
                /*
                 * 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_obj(&btp->bt_lru, &bp->b_lru);
                } else {
                        ASSERT(list_empty(&bp->b_lru));
                }

                ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
                rhashtable_remove_fast(&bch->bc_hash, &bp->b_rhash_head,
                                xfs_buf_hash_params);
                if (pag)
                        xfs_perag_put(pag);
                freebuf = true;
        }

out_unlock:
        spin_unlock(&bp->b_lock);

        if (freebuf)
                xfs_buf_free(bp);
}

/*
 * Release a hold on the specified buffer.
 */
void
xfs_buf_rele(
        struct xfs_buf          *bp)
{
        trace_xfs_buf_rele(bp, _RET_IP_);
        if (xfs_buf_is_uncached(bp))
                xfs_buf_rele_uncached(bp);
        else
                xfs_buf_rele_cached(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;
        struct xfs_log_item     *lip;

        /*
         * 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. */
        list_for_each_entry(lip, &bp->b_li_list, li_bio_list) {
                set_bit(XFS_LI_FAILED, &lip->li_flags);
                clear_bit(XFS_LI_FLUSHING, &lip->li_flags);
        }

        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);
        reinit_completion(&bp->b_iowait);
        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;
}

/* returns false if the caller needs to resubmit the I/O, else true */
static bool
__xfs_buf_ioend(
        struct xfs_buf  *bp)
{
        trace_xfs_buf_iodone(bp, _RET_IP_);

        if (bp->b_flags & XBF_READ) {
                if (!bp->b_error && is_vmalloc_addr(bp->b_addr))
                        invalidate_kernel_vmap_range(bp->b_addr,
                                roundup(BBTOB(bp->b_length), PAGE_SIZE));
                if (!bp->b_error && bp->b_ops)
                        bp->b_ops->verify_read(bp);
                if (!bp->b_error)
                        bp->b_flags |= XBF_DONE;
                if (bp->b_flags & XBF_READ_AHEAD)
                        percpu_counter_dec(&bp->b_target->bt_readahead_count);
        } 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 false;

                /* 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_iodone)
                        bp->b_iodone(bp);
        }

        bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD |
                         _XBF_LOGRECOVERY);
        return true;
}

static void
xfs_buf_ioend(
        struct xfs_buf  *bp)
{
        if (!__xfs_buf_ioend(bp))
                return;
        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);

        if (__xfs_buf_ioend(bp))
                xfs_buf_relse(bp);
}

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);

        xfs_buf_submit(bp);
        error = xfs_buf_iowait(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 = bio->bi_private;

        if (bio->bi_status)
                xfs_buf_ioerror(bp, blk_status_to_errno(bio->bi_status));
        else if ((bp->b_flags & XBF_WRITE) && (bp->b_flags & XBF_ASYNC) &&
                 XFS_TEST_ERROR(bp->b_mount, XFS_ERRTAG_BUF_IOERROR))
                xfs_buf_ioerror(bp, -EIO);

        if (bp->b_flags & XBF_ASYNC) {
                INIT_WORK(&bp->b_ioend_work, xfs_buf_ioend_work);
                queue_work(bp->b_mount->m_buf_workqueue, &bp->b_ioend_work);
        } else {
                complete(&bp->b_iowait);
        }

        bio_put(bio);
}

static inline blk_opf_t
xfs_buf_bio_op(
        struct xfs_buf          *bp)
{
        blk_opf_t               op;

        if (bp->b_flags & XBF_WRITE) {
                op = REQ_OP_WRITE;
        } else {
                op = REQ_OP_READ;
                if (bp->b_flags & XBF_READ_AHEAD)
                        op |= REQ_RAHEAD;
        }

        return op | REQ_META;
}

static void
xfs_buf_submit_bio(
        struct xfs_buf          *bp)
{
        unsigned int            len = BBTOB(bp->b_length);
        unsigned int            nr_vecs = bio_add_max_vecs(bp->b_addr, len);
        unsigned int            map = 0;
        struct blk_plug         plug;
        struct bio              *bio;

        bio = bio_alloc(bp->b_target->bt_bdev, nr_vecs, xfs_buf_bio_op(bp),
                        GFP_NOIO);
        if (is_vmalloc_addr(bp->b_addr))
                bio_add_vmalloc(bio, bp->b_addr, len);
        else
                bio_add_virt_nofail(bio, bp->b_addr, len);
        bio->bi_private = bp;
        bio->bi_end_io = xfs_buf_bio_end_io;

        /*
         * If there is more than one map segment, split out a new bio for each
         * map except of the last one.  The last map is handled by the
         * remainder of the original bio outside the loop.
         */
        blk_start_plug(&plug);
        for (map = 0; map < bp->b_map_count - 1; map++) {
                struct bio      *split;

                split = bio_split(bio, bp->b_maps[map].bm_len, GFP_NOFS,
                                &fs_bio_set);
                split->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
                bio_chain(split, bio);
                submit_bio(split);
        }
        bio->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
        submit_bio(bio);
        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));

        do {
                trace_xfs_buf_iowait(bp, _RET_IP_);
                wait_for_completion(&bp->b_iowait);
                trace_xfs_buf_iowait_done(bp, _RET_IP_);
        } while (!__xfs_buf_ioend(bp));

        return bp->b_error;
}

/*
 * Run the write verifier callback function if it exists. If this fails, mark
 * the buffer with an error and do not dispatch the I/O.
 */
static bool
xfs_buf_verify_write(
        struct xfs_buf          *bp)
{
        if (bp->b_ops) {
                bp->b_ops->verify_write(bp);
                if (bp->b_error)
                        return false;
        } else if (bp->b_rhash_key != XFS_BUF_DADDR_NULL) {
                /*
                 * Non-crc filesystems don't attach verifiers during log
                 * recovery, so don't warn for such filesystems.
                 */
                if (xfs_has_crc(bp->b_mount)) {
                        xfs_warn(bp->b_mount,
                                "%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();
                }
        }

        return true;
}

/*
 * 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 void
xfs_buf_submit(
        struct xfs_buf  *bp)
{
        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;
        }

        if (bp->b_flags & XBF_WRITE)
                xfs_buf_wait_unpin(bp);

        /*
         * 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) && !xfs_buf_verify_write(bp)) {
                xfs_force_shutdown(bp->b_mount, SHUTDOWN_CORRUPT_INCORE);
                xfs_buf_ioend(bp);
                return;
        }

        /* In-memory targets are directly mapped, no I/O required. */
        if (xfs_buftarg_is_mem(bp->b_target)) {
                xfs_buf_ioend(bp);
                return;
        }

        xfs_buf_submit_bio(bp);
}

/*
 * 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,
        void                    *arg)

{
        struct xfs_buf          *bp = container_of(item, struct xfs_buf, b_lru);
        struct list_head        *dispose = arg;

        if (!spin_trylock(&bp->b_lock))
                return LRU_SKIP;
        if (bp->b_hold > 1) {
                /* need to wait, so skip it this pass */
                spin_unlock(&bp->b_lock);
                trace_xfs_buf_drain_buftarg(bp, _RET_IP_);
                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 for all in-flight readahead 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_readahead_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,
        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 = shrink->private_data;
        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 = shrink->private_data;
        return list_lru_shrink_count(&btp->bt_lru, sc);
}

void
xfs_destroy_buftarg(
        struct xfs_buftarg      *btp)
{
        shrinker_free(btp->bt_shrinker);
        ASSERT(percpu_counter_sum(&btp->bt_readahead_count) == 0);
        percpu_counter_destroy(&btp->bt_readahead_count);
        list_lru_destroy(&btp->bt_lru);
}

void
xfs_free_buftarg(
        struct xfs_buftarg      *btp)
{
        xfs_destroy_buftarg(btp);
        fs_put_dax(btp->bt_daxdev, btp->bt_mount);
        /* the main block device is closed by kill_block_super */
        if (btp->bt_bdev != btp->bt_mount->m_super->s_bdev)
                bdev_fput(btp->bt_file);
        kfree(btp);
}

/*
 * Configure this buffer target for hardware-assisted atomic writes if the
 * underlying block device supports is congruent with the filesystem geometry.
 */
static inline void
xfs_configure_buftarg_atomic_writes(
        struct xfs_buftarg      *btp)
{
        struct xfs_mount        *mp = btp->bt_mount;
        unsigned int            min_bytes, max_bytes;

        min_bytes = bdev_atomic_write_unit_min_bytes(btp->bt_bdev);
        max_bytes = bdev_atomic_write_unit_max_bytes(btp->bt_bdev);

        /*
         * Ignore atomic write geometry that is nonsense or doesn't even cover
         * a single fsblock.
         */
        if (min_bytes > max_bytes ||
            min_bytes > mp->m_sb.sb_blocksize ||
            max_bytes < mp->m_sb.sb_blocksize) {
                min_bytes = 0;
                max_bytes = 0;
        }

        btp->bt_awu_min = min_bytes;
        btp->bt_awu_max = max_bytes;
}

/* Configure a buffer target that abstracts a block device. */
int
xfs_configure_buftarg(
        struct xfs_buftarg      *btp,
        unsigned int            sectorsize,
        xfs_rfsblock_t          nr_blocks)
{
        struct xfs_mount        *mp = btp->bt_mount;

        if (btp->bt_bdev) {
                int             error;

                error = bdev_validate_blocksize(btp->bt_bdev, sectorsize);
                if (error) {
                        xfs_warn(mp,
                                "Cannot use blocksize %u on device %pg, err %d",
                                sectorsize, btp->bt_bdev, error);
                        return -EINVAL;
                }

                if (bdev_can_atomic_write(btp->bt_bdev))
                        xfs_configure_buftarg_atomic_writes(btp);
        }

        btp->bt_meta_sectorsize = sectorsize;
        btp->bt_meta_sectormask = sectorsize - 1;
        /* m_blkbb_log is not set up yet */
        btp->bt_nr_sectors = nr_blocks << (mp->m_sb.sb_blocklog - BBSHIFT);
        return 0;
}

int
xfs_init_buftarg(
        struct xfs_buftarg              *btp,
        size_t                          logical_sectorsize,
        const char                      *descr)
{
        /* The maximum size of the buftarg is only known once the sb is read. */
        btp->bt_nr_sectors = XFS_BUF_DADDR_MAX;

        /* Set up device logical sector size mask */
        btp->bt_logical_sectorsize = logical_sectorsize;
        btp->bt_logical_sectormask = logical_sectorsize - 1;

        /*
         * 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 (list_lru_init(&btp->bt_lru))
                return -ENOMEM;
        if (percpu_counter_init(&btp->bt_readahead_count, 0, GFP_KERNEL))
                goto out_destroy_lru;

        btp->bt_shrinker =
                shrinker_alloc(SHRINKER_NUMA_AWARE, "xfs-buf:%s", descr);
        if (!btp->bt_shrinker)
                goto out_destroy_io_count;
        btp->bt_shrinker->count_objects = xfs_buftarg_shrink_count;
        btp->bt_shrinker->scan_objects = xfs_buftarg_shrink_scan;
        btp->bt_shrinker->private_data = btp;
        shrinker_register(btp->bt_shrinker);
        return 0;

out_destroy_io_count:
        percpu_counter_destroy(&btp->bt_readahead_count);
out_destroy_lru:
        list_lru_destroy(&btp->bt_lru);
        return -ENOMEM;
}

struct xfs_buftarg *
xfs_alloc_buftarg(
        struct xfs_mount        *mp,
        struct file             *bdev_file)
{
        struct xfs_buftarg      *btp;
        const struct dax_holder_operations *ops = NULL;
        int                     error;


#if defined(CONFIG_FS_DAX) && defined(CONFIG_MEMORY_FAILURE)
        ops = &xfs_dax_holder_operations;
#endif
        btp = kzalloc_obj(*btp, GFP_KERNEL | __GFP_NOFAIL);

        btp->bt_mount = mp;
        btp->bt_file = bdev_file;
        btp->bt_bdev = file_bdev(bdev_file);
        btp->bt_dev = btp->bt_bdev->bd_dev;
        btp->bt_daxdev = fs_dax_get_by_bdev(btp->bt_bdev, &btp->bt_dax_part_off,
                                            mp, ops);

        /*
         * Flush and invalidate all devices' pagecaches before reading any
         * metadata because XFS doesn't use the bdev pagecache.
         */
        error = sync_blockdev(btp->bt_bdev);
        if (error)
                goto error_free;

        /*
         * When allocating the buftargs we have not yet read the super block and
         * thus don't know the file system sector size yet.
         */
        btp->bt_meta_sectorsize = bdev_logical_block_size(btp->bt_bdev);
        btp->bt_meta_sectormask = btp->bt_meta_sectorsize - 1;

        error = xfs_init_buftarg(btp, btp->bt_meta_sectorsize,
                                mp->m_super->s_id);
        if (error)
                goto error_free;

        return btp;

error_free:
        kfree(btp);
        return ERR_PTR(error);
}

static inline void
xfs_buf_list_del(
        struct xfs_buf          *bp)
{
        list_del_init(&bp->b_list);
        wake_up_var(&bp->b_list);
}

/*
 * 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;
                xfs_buf_list_del(bp);
                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)) {
                xfs_buf_hold(bp);
                list_add_tail(&bp->b_list, list);
        }

        return true;
}

/*
 * Queue a buffer to this delwri list as part of a data integrity operation.
 * If the buffer is on any other delwri list, we'll wait for that to clear
 * so that the caller can submit the buffer for IO and wait for the result.
 * Callers must ensure the buffer is not already on the list.
 */
void
xfs_buf_delwri_queue_here(
        struct xfs_buf          *bp,
        struct list_head        *buffer_list)
{
        /*
         * We need this buffer to end up on the /caller's/ delwri list, not any
         * old list.  This can happen if the buffer is marked stale (which
         * clears DELWRI_Q) after the AIL queues the buffer to its list but
         * before the AIL has a chance to submit the list.
         */
        while (!list_empty(&bp->b_list)) {
                xfs_buf_unlock(bp);
                wait_var_event(&bp->b_list, list_empty(&bp->b_list));
                xfs_buf_lock(bp);
        }

        ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));

        xfs_buf_delwri_queue(bp, buffer_list);
}

/*
 * 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;
}

static bool
xfs_buf_delwri_submit_prep(
        struct xfs_buf          *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)) {
                xfs_buf_list_del(bp);
                xfs_buf_relse(bp);
                return false;
        }

        trace_xfs_buf_delwri_split(bp, _RET_IP_);
        bp->b_flags &= ~_XBF_DELWRI_Q;
        bp->b_flags |= XBF_WRITE;
        return true;
}

/*
 * 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)
{
        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 (!xfs_buf_trylock(bp))
                        continue;
                if (xfs_buf_ispinned(bp)) {
                        xfs_buf_unlock(bp);
                        pinned++;
                        continue;
                }
                if (!xfs_buf_delwri_submit_prep(bp))
                        continue;
                bp->b_flags |= XBF_ASYNC;
                xfs_buf_list_del(bp);
                xfs_buf_submit(bp);
        }
        blk_finish_plug(&plug);

        return pinned;
}

/*
 * 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, *n;
        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) {
                xfs_buf_lock(bp);
                if (!xfs_buf_delwri_submit_prep(bp))
                        continue;
                bp->b_flags &= ~XBF_ASYNC;
                list_move_tail(&bp->b_list, &wait_list);
                xfs_buf_submit(bp);
        }
        blk_finish_plug(&plug);

        /* Wait for IO to complete. */
        while (!list_empty(&wait_list)) {
                bp = list_first_entry(&wait_list, struct xfs_buf, b_list);

                xfs_buf_list_del(bp);

                /*
                 * 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;
}

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(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];
}