xfs_filestream.c

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/*
 * Copyright (c) 2006-2007 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_bmap_btree.h"
#include "xfs_inum.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_ag.h"
#include "xfs_log.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_mount.h"
#include "xfs_bmap.h"
#include "xfs_alloc.h"
#include "xfs_utils.h"
#include "xfs_mru_cache.h"
#include "xfs_filestream.h"
#include "xfs_trace.h"

#ifdef XFS_FILESTREAMS_TRACE

ktrace_t *xfs_filestreams_trace_buf;

STATIC void
xfs_filestreams_trace(
    xfs_mount_t *mp,    /* mount point */
    int     type,   /* type of trace */
    const char  *func,  /* source function */
    int     line,   /* source line number */
    __psunsigned_t  arg0,
    __psunsigned_t  arg1,
    __psunsigned_t  arg2,
    __psunsigned_t  arg3,
    __psunsigned_t  arg4,
    __psunsigned_t  arg5)
{
    ktrace_enter(xfs_filestreams_trace_buf,
        (void *)(__psint_t)(type | (line << 16)),
        (void *)func,
        (void *)(__psunsigned_t)current_pid(),
        (void *)mp,
        (void *)(__psunsigned_t)arg0,
        (void *)(__psunsigned_t)arg1,
        (void *)(__psunsigned_t)arg2,
        (void *)(__psunsigned_t)arg3,
        (void *)(__psunsigned_t)arg4,
        (void *)(__psunsigned_t)arg5,
        NULL, NULL, NULL, NULL, NULL, NULL);
}

#define TRACE0(mp,t)            TRACE6(mp,t,0,0,0,0,0,0)
#define TRACE1(mp,t,a0)         TRACE6(mp,t,a0,0,0,0,0,0)
#define TRACE2(mp,t,a0,a1)      TRACE6(mp,t,a0,a1,0,0,0,0)
#define TRACE3(mp,t,a0,a1,a2)       TRACE6(mp,t,a0,a1,a2,0,0,0)
#define TRACE4(mp,t,a0,a1,a2,a3)    TRACE6(mp,t,a0,a1,a2,a3,0,0)
#define TRACE5(mp,t,a0,a1,a2,a3,a4) TRACE6(mp,t,a0,a1,a2,a3,a4,0)
#define TRACE6(mp,t,a0,a1,a2,a3,a4,a5) \
    xfs_filestreams_trace(mp, t, __func__, __LINE__, \
                (__psunsigned_t)a0, (__psunsigned_t)a1, \
                (__psunsigned_t)a2, (__psunsigned_t)a3, \
                (__psunsigned_t)a4, (__psunsigned_t)a5)

#define TRACE_AG_SCAN(mp, ag, ag2) \
        TRACE2(mp, XFS_FSTRM_KTRACE_AGSCAN, ag, ag2);
#define TRACE_AG_PICK1(mp, max_ag, maxfree) \
        TRACE2(mp, XFS_FSTRM_KTRACE_AGPICK1, max_ag, maxfree);
#define TRACE_AG_PICK2(mp, ag, ag2, cnt, free, scan, flag) \
        TRACE6(mp, XFS_FSTRM_KTRACE_AGPICK2, ag, ag2, \
             cnt, free, scan, flag)
#define TRACE_UPDATE(mp, ip, ag, cnt, ag2, cnt2) \
        TRACE5(mp, XFS_FSTRM_KTRACE_UPDATE, ip, ag, cnt, ag2, cnt2)
#define TRACE_FREE(mp, ip, pip, ag, cnt) \
        TRACE4(mp, XFS_FSTRM_KTRACE_FREE, ip, pip, ag, cnt)
#define TRACE_LOOKUP(mp, ip, pip, ag, cnt) \
        TRACE4(mp, XFS_FSTRM_KTRACE_ITEM_LOOKUP, ip, pip, ag, cnt)
#define TRACE_ASSOCIATE(mp, ip, pip, ag, cnt) \
        TRACE4(mp, XFS_FSTRM_KTRACE_ASSOCIATE, ip, pip, ag, cnt)
#define TRACE_MOVEAG(mp, ip, pip, oag, ocnt, nag, ncnt) \
        TRACE6(mp, XFS_FSTRM_KTRACE_MOVEAG, ip, pip, oag, ocnt, nag, ncnt)
#define TRACE_ORPHAN(mp, ip, ag) \
        TRACE2(mp, XFS_FSTRM_KTRACE_ORPHAN, ip, ag);


#else
#define TRACE_AG_SCAN(mp, ag, ag2)
#define TRACE_AG_PICK1(mp, max_ag, maxfree)
#define TRACE_AG_PICK2(mp, ag, ag2, cnt, free, scan, flag)
#define TRACE_UPDATE(mp, ip, ag, cnt, ag2, cnt2)
#define TRACE_FREE(mp, ip, pip, ag, cnt)
#define TRACE_LOOKUP(mp, ip, pip, ag, cnt)
#define TRACE_ASSOCIATE(mp, ip, pip, ag, cnt)
#define TRACE_MOVEAG(mp, ip, pip, oag, ocnt, nag, ncnt)
#define TRACE_ORPHAN(mp, ip, ag)
#endif

static kmem_zone_t *item_zone;

/*
 * Structure for associating a file or a directory with an allocation group.
 * The parent directory pointer is only needed for files, but since there will
 * generally be vastly more files than directories in the cache, using the same
 * data structure simplifies the code with very little memory overhead.
 */
typedef struct fstrm_item
{
    xfs_agnumber_t  ag; /* AG currently in use for the file/directory. */
    xfs_inode_t *ip;    /* inode self-pointer. */
    xfs_inode_t *pip;   /* Parent directory inode pointer. */
} fstrm_item_t;

/*
 * Allocation group filestream associations are tracked with per-ag atomic
 * counters.  These counters allow _xfs_filestream_pick_ag() to tell whether a
 * particular AG already has active filestreams associated with it. The mount
 * point's m_peraglock is used to protect these counters from per-ag array
 * re-allocation during a growfs operation.  When xfs_growfs_data_private() is
 * about to reallocate the array, it calls xfs_filestream_flush() with the
 * m_peraglock held in write mode.
 *
 * Since xfs_mru_cache_flush() guarantees that all the free functions for all
 * the cache elements have finished executing before it returns, it's safe for
 * the free functions to use the atomic counters without m_peraglock protection.
 * This allows the implementation of xfs_fstrm_free_func() to be agnostic about
 * whether it was called with the m_peraglock held in read mode, write mode or
 * not held at all.  The race condition this addresses is the following:
 *
 *  - The work queue scheduler fires and pulls a filestream directory cache
 *    element off the LRU end of the cache for deletion, then gets pre-empted.
 *  - A growfs operation grabs the m_peraglock in write mode, flushes all the
 *    remaining items from the cache and reallocates the mount point's per-ag
 *    array, resetting all the counters to zero.
 *  - The work queue thread resumes and calls the free function for the element
 *    it started cleaning up earlier.  In the process it decrements the
 *    filestreams counter for an AG that now has no references.
 *
 * With a shrinkfs feature, the above scenario could panic the system.
 *
 * All other uses of the following macros should be protected by either the
 * m_peraglock held in read mode, or the cache's internal locking exposed by the
 * interval between a call to xfs_mru_cache_lookup() and a call to
 * xfs_mru_cache_done().  In addition, the m_peraglock must be held in read mode
 * when new elements are added to the cache.
 *
 * Combined, these locking rules ensure that no associations will ever exist in
 * the cache that reference per-ag array elements that have since been
 * reallocated.
 */
static int
xfs_filestream_peek_ag(
    xfs_mount_t *mp,
    xfs_agnumber_t  agno)
{
    struct xfs_perag *pag;
    int     ret;

    pag = xfs_perag_get(mp, agno);
    ret = atomic_read(&pag->pagf_fstrms);
    xfs_perag_put(pag);
    return ret;
}

static int
xfs_filestream_get_ag(
    xfs_mount_t *mp,
    xfs_agnumber_t  agno)
{
    struct xfs_perag *pag;
    int     ret;

    pag = xfs_perag_get(mp, agno);
    ret = atomic_inc_return(&pag->pagf_fstrms);
    xfs_perag_put(pag);
    return ret;
}

static void
xfs_filestream_put_ag(
    xfs_mount_t *mp,
    xfs_agnumber_t  agno)
{
    struct xfs_perag *pag;

    pag = xfs_perag_get(mp, agno);
    atomic_dec(&pag->pagf_fstrms);
    xfs_perag_put(pag);
}

/*
 * Scan the AGs starting at startag looking for an AG that isn't in use and has
 * at least minlen blocks free.
 */
static int
_xfs_filestream_pick_ag(
    xfs_mount_t *mp,
    xfs_agnumber_t  startag,
    xfs_agnumber_t  *agp,
    int     flags,
    xfs_extlen_t    minlen)
{
    int     streams, max_streams;
    int     err, trylock, nscan;
    xfs_extlen_t    longest, free, minfree, maxfree = 0;
    xfs_agnumber_t  ag, max_ag = NULLAGNUMBER;
    struct xfs_perag *pag;

    /* 2% of an AG's blocks must be free for it to be chosen. */
    minfree = mp->m_sb.sb_agblocks / 50;

    ag = startag;
    *agp = NULLAGNUMBER;

    /* For the first pass, don't sleep trying to init the per-AG. */
    trylock = XFS_ALLOC_FLAG_TRYLOCK;

    for (nscan = 0; 1; nscan++) {
        pag = xfs_perag_get(mp, ag);
        TRACE_AG_SCAN(mp, ag, atomic_read(&pag->pagf_fstrms));

        if (!pag->pagf_init) {
            err = xfs_alloc_pagf_init(mp, NULL, ag, trylock);
            if (err && !trylock) {
                xfs_perag_put(pag);
                return err;
            }
        }

        /* Might fail sometimes during the 1st pass with trylock set. */
        if (!pag->pagf_init)
            goto next_ag;

        /* Keep track of the AG with the most free blocks. */
        if (pag->pagf_freeblks > maxfree) {
            maxfree = pag->pagf_freeblks;
            max_streams = atomic_read(&pag->pagf_fstrms);
            max_ag = ag;
        }

        /*
         * The AG reference count does two things: it enforces mutual
         * exclusion when examining the suitability of an AG in this
         * loop, and it guards against two filestreams being established
         * in the same AG as each other.
         */
        if (xfs_filestream_get_ag(mp, ag) > 1) {
            xfs_filestream_put_ag(mp, ag);
            goto next_ag;
        }

        longest = xfs_alloc_longest_free_extent(mp, pag);
        if (((minlen && longest >= minlen) ||
             (!minlen && pag->pagf_freeblks >= minfree)) &&
            (!pag->pagf_metadata || !(flags & XFS_PICK_USERDATA) ||
             (flags & XFS_PICK_LOWSPACE))) {

            /* Break out, retaining the reference on the AG. */
            free = pag->pagf_freeblks;
            streams = atomic_read(&pag->pagf_fstrms);
            xfs_perag_put(pag);
            *agp = ag;
            break;
        }

        /* Drop the reference on this AG, it's not usable. */
        xfs_filestream_put_ag(mp, ag);
next_ag:
        xfs_perag_put(pag);
        /* Move to the next AG, wrapping to AG 0 if necessary. */
        if (++ag >= mp->m_sb.sb_agcount)
            ag = 0;

        /* If a full pass of the AGs hasn't been done yet, continue. */
        if (ag != startag)
            continue;

        /* Allow sleeping in xfs_alloc_pagf_init() on the 2nd pass. */
        if (trylock != 0) {
            trylock = 0;
            continue;
        }

        /* Finally, if lowspace wasn't set, set it for the 3rd pass. */
        if (!(flags & XFS_PICK_LOWSPACE)) {
            flags |= XFS_PICK_LOWSPACE;
            continue;
        }

        /*
         * Take the AG with the most free space, regardless of whether
         * it's already in use by another filestream.
         */
        if (max_ag != NULLAGNUMBER) {
            xfs_filestream_get_ag(mp, max_ag);
            TRACE_AG_PICK1(mp, max_ag, maxfree);
            streams = max_streams;
            free = maxfree;
            *agp = max_ag;
            break;
        }

        /* take AG 0 if none matched */
        TRACE_AG_PICK1(mp, max_ag, maxfree);
        *agp = 0;
        return 0;
    }

    TRACE_AG_PICK2(mp, startag, *agp, streams, free, nscan, flags);

    return 0;
}

/*
 * Set the allocation group number for a file or a directory, updating inode
 * references and per-AG references as appropriate.
 */
static int
_xfs_filestream_update_ag(
    xfs_inode_t *ip,
    xfs_inode_t *pip,
    xfs_agnumber_t  ag)
{
    int     err = 0;
    xfs_mount_t *mp;
    xfs_mru_cache_t *cache;
    fstrm_item_t    *item;
    xfs_agnumber_t  old_ag;
    xfs_inode_t *old_pip;

    /*
     * Either ip is a regular file and pip is a directory, or ip is a
     * directory and pip is NULL.
     */
    ASSERT(ip && ((S_ISREG(ip->i_d.di_mode) && pip &&
                   S_ISDIR(pip->i_d.di_mode)) ||
                  (S_ISDIR(ip->i_d.di_mode) && !pip)));

    mp = ip->i_mount;
    cache = mp->m_filestream;

    item = xfs_mru_cache_lookup(cache, ip->i_ino);
    if (item) {
        ASSERT(item->ip == ip);
        old_ag = item->ag;
        item->ag = ag;
        old_pip = item->pip;
        item->pip = pip;
        xfs_mru_cache_done(cache);

        /*
         * If the AG has changed, drop the old ref and take a new one,
         * effectively transferring the reference from old to new AG.
         */
        if (ag != old_ag) {
            xfs_filestream_put_ag(mp, old_ag);
            xfs_filestream_get_ag(mp, ag);
        }

        /*
         * If ip is a file and its pip has changed, drop the old ref and
         * take a new one.
         */
        if (pip && pip != old_pip) {
            IRELE(old_pip);
            IHOLD(pip);
        }

        TRACE_UPDATE(mp, ip, old_ag, xfs_filestream_peek_ag(mp, old_ag),
                ag, xfs_filestream_peek_ag(mp, ag));
        return 0;
    }

    item = kmem_zone_zalloc(item_zone, KM_MAYFAIL);
    if (!item)
        return ENOMEM;

    item->ag = ag;
    item->ip = ip;
    item->pip = pip;

    err = xfs_mru_cache_insert(cache, ip->i_ino, item);
    if (err) {
        kmem_zone_free(item_zone, item);
        return err;
    }

    /* Take a reference on the AG. */
    xfs_filestream_get_ag(mp, ag);

    /*
     * Take a reference on the inode itself regardless of whether it's a
     * regular file or a directory.
     */
    IHOLD(ip);

    /*
     * In the case of a regular file, take a reference on the parent inode
     * as well to ensure it remains in-core.
     */
    if (pip)
        IHOLD(pip);

    TRACE_UPDATE(mp, ip, ag, xfs_filestream_peek_ag(mp, ag),
            ag, xfs_filestream_peek_ag(mp, ag));

    return 0;
}

/* xfs_fstrm_free_func(): callback for freeing cached stream items. */
STATIC void
xfs_fstrm_free_func(
    unsigned long   ino,
    void        *data)
{
    fstrm_item_t    *item  = (fstrm_item_t *)data;
    xfs_inode_t *ip = item->ip;

    ASSERT(ip->i_ino == ino);

    xfs_iflags_clear(ip, XFS_IFILESTREAM);

    /* Drop the reference taken on the AG when the item was added. */
    xfs_filestream_put_ag(ip->i_mount, item->ag);

    TRACE_FREE(ip->i_mount, ip, item->pip, item->ag,
        xfs_filestream_peek_ag(ip->i_mount, item->ag));

    /*
     * _xfs_filestream_update_ag() always takes a reference on the inode
     * itself, whether it's a file or a directory.  Release it here.
     * This can result in the inode being freed and so we must
     * not hold any inode locks when freeing filesstreams objects
     * otherwise we can deadlock here.
     */
    IRELE(ip);

    /*
     * In the case of a regular file, _xfs_filestream_update_ag() also
     * takes a ref on the parent inode to keep it in-core.  Release that
     * too.
     */
    if (item->pip)
        IRELE(item->pip);

    /* Finally, free the memory allocated for the item. */
    kmem_zone_free(item_zone, item);
}

/*
 * xfs_filestream_init() is called at xfs initialisation time to set up the
 * memory zone that will be used for filestream data structure allocation.
 */
int
xfs_filestream_init(void)
{
    item_zone = kmem_zone_init(sizeof(fstrm_item_t), "fstrm_item");
    if (!item_zone)
        return -ENOMEM;

    return 0;
}

/*
 * xfs_filestream_uninit() is called at xfs termination time to destroy the
 * memory zone that was used for filestream data structure allocation.
 */
void
xfs_filestream_uninit(void)
{
    kmem_zone_destroy(item_zone);
}

/*
 * xfs_filestream_mount() is called when a file system is mounted with the
 * filestream option.  It is responsible for allocating the data structures
 * needed to track the new file system's file streams.
 */
int
xfs_filestream_mount(
    xfs_mount_t *mp)
{
    int     err;
    unsigned int    lifetime, grp_count;

    /*
     * The filestream timer tunable is currently fixed within the range of
     * one second to four minutes, with five seconds being the default.  The
     * group count is somewhat arbitrary, but it'd be nice to adhere to the
     * timer tunable to within about 10 percent.  This requires at least 10
     * groups.
     */
    lifetime  = xfs_fstrm_centisecs * 10;
    grp_count = 10;

    err = xfs_mru_cache_create(&mp->m_filestream, lifetime, grp_count,
                         xfs_fstrm_free_func);

    return err;
}

/*
 * xfs_filestream_unmount() is called when a file system that was mounted with
 * the filestream option is unmounted.  It drains the data structures created
 * to track the file system's file streams and frees all the memory that was
 * allocated.
 */
void
xfs_filestream_unmount(
    xfs_mount_t *mp)
{
    xfs_mru_cache_destroy(mp->m_filestream);
}

/*
 * Return the AG of the filestream the file or directory belongs to, or
 * NULLAGNUMBER otherwise.
 */
xfs_agnumber_t
xfs_filestream_lookup_ag(
    xfs_inode_t *ip)
{
    xfs_mru_cache_t *cache;
    fstrm_item_t    *item;
    xfs_agnumber_t  ag;
    int     ref;

    if (!S_ISREG(ip->i_d.di_mode) && !S_ISDIR(ip->i_d.di_mode)) {
        ASSERT(0);
        return NULLAGNUMBER;
    }

    cache = ip->i_mount->m_filestream;
    item = xfs_mru_cache_lookup(cache, ip->i_ino);
    if (!item) {
        TRACE_LOOKUP(ip->i_mount, ip, NULL, NULLAGNUMBER, 0);
        return NULLAGNUMBER;
    }

    ASSERT(ip == item->ip);
    ag = item->ag;
    ref = xfs_filestream_peek_ag(ip->i_mount, ag);
    xfs_mru_cache_done(cache);

    TRACE_LOOKUP(ip->i_mount, ip, item->pip, ag, ref);
    return ag;
}

/*
 * xfs_filestream_associate() should only be called to associate a regular file
 * with its parent directory.  Calling it with a child directory isn't
 * appropriate because filestreams don't apply to entire directory hierarchies.
 * Creating a file in a child directory of an existing filestream directory
 * starts a new filestream with its own allocation group association.
 *
 * Returns < 0 on error, 0 if successful association occurred, > 0 if
 * we failed to get an association because of locking issues.
 */
int
xfs_filestream_associate(
    xfs_inode_t *pip,
    xfs_inode_t *ip)
{
    xfs_mount_t *mp;
    xfs_mru_cache_t *cache;
    fstrm_item_t    *item;
    xfs_agnumber_t  ag, rotorstep, startag;
    int     err = 0;

    ASSERT(S_ISDIR(pip->i_d.di_mode));
    ASSERT(S_ISREG(ip->i_d.di_mode));
    if (!S_ISDIR(pip->i_d.di_mode) || !S_ISREG(ip->i_d.di_mode))
        return -EINVAL;

    mp = pip->i_mount;
    cache = mp->m_filestream;

    /*
     * We have a problem, Houston.
     *
     * Taking the iolock here violates inode locking order - we already
     * hold the ilock. Hence if we block getting this lock we may never
     * wake. Unfortunately, that means if we can't get the lock, we're
     * screwed in terms of getting a stream association - we can't spin
     * waiting for the lock because someone else is waiting on the lock we
     * hold and we cannot drop that as we are in a transaction here.
     *
     * Lucky for us, this inversion is not a problem because it's a
     * directory inode that we are trying to lock here.
     *
     * So, if we can't get the iolock without sleeping then just give up
     */
    if (!xfs_ilock_nowait(pip, XFS_IOLOCK_EXCL))
        return 1;

    /* If the parent directory is already in the cache, use its AG. */
    item = xfs_mru_cache_lookup(cache, pip->i_ino);
    if (item) {
        ASSERT(item->ip == pip);
        ag = item->ag;
        xfs_mru_cache_done(cache);

        TRACE_LOOKUP(mp, pip, pip, ag, xfs_filestream_peek_ag(mp, ag));
        err = _xfs_filestream_update_ag(ip, pip, ag);

        goto exit;
    }

    /*
     * Set the starting AG using the rotor for inode32, otherwise
     * use the directory inode's AG.
     */
    if (mp->m_flags & XFS_MOUNT_32BITINODES) {
        rotorstep = xfs_rotorstep;
        startag = (mp->m_agfrotor / rotorstep) % mp->m_sb.sb_agcount;
        mp->m_agfrotor = (mp->m_agfrotor + 1) %
                         (mp->m_sb.sb_agcount * rotorstep);
    } else
        startag = XFS_INO_TO_AGNO(mp, pip->i_ino);

    /* Pick a new AG for the parent inode starting at startag. */
    err = _xfs_filestream_pick_ag(mp, startag, &ag, 0, 0);
    if (err || ag == NULLAGNUMBER)
        goto exit_did_pick;

    /* Associate the parent inode with the AG. */
    err = _xfs_filestream_update_ag(pip, NULL, ag);
    if (err)
        goto exit_did_pick;

    /* Associate the file inode with the AG. */
    err = _xfs_filestream_update_ag(ip, pip, ag);
    if (err)
        goto exit_did_pick;

    TRACE_ASSOCIATE(mp, ip, pip, ag, xfs_filestream_peek_ag(mp, ag));

exit_did_pick:
    /*
     * If _xfs_filestream_pick_ag() returned a valid AG, remove the
     * reference it took on it, since the file and directory will have taken
     * their own now if they were successfully cached.
     */
    if (ag != NULLAGNUMBER)
        xfs_filestream_put_ag(mp, ag);

exit:
    xfs_iunlock(pip, XFS_IOLOCK_EXCL);
    return -err;
}

/*
 * Pick a new allocation group for the current file and its file stream.  This
 * function is called by xfs_bmap_filestreams() with the mount point's per-ag
 * lock held.
 */
int
xfs_filestream_new_ag(
    xfs_bmalloca_t  *ap,
    xfs_agnumber_t  *agp)
{
    int     flags, err;
    xfs_inode_t *ip, *pip = NULL;
    xfs_mount_t *mp;
    xfs_mru_cache_t *cache;
    xfs_extlen_t    minlen;
    fstrm_item_t    *dir, *file;
    xfs_agnumber_t  ag = NULLAGNUMBER;

    ip = ap->ip;
    mp = ip->i_mount;
    cache = mp->m_filestream;
    minlen = ap->length;
    *agp = NULLAGNUMBER;

    /*
     * Look for the file in the cache, removing it if it's found.  Doing
     * this allows it to be held across the dir lookup that follows.
     */
    file = xfs_mru_cache_remove(cache, ip->i_ino);
    if (file) {
        ASSERT(ip == file->ip);

        /* Save the file's parent inode and old AG number for later. */
        pip = file->pip;
        ag = file->ag;

        /* Look for the file's directory in the cache. */
        dir = xfs_mru_cache_lookup(cache, pip->i_ino);
        if (dir) {
            ASSERT(pip == dir->ip);

            /*
             * If the directory has already moved on to a new AG,
             * use that AG as the new AG for the file. Don't
             * forget to twiddle the AG refcounts to match the
             * movement.
             */
            if (dir->ag != file->ag) {
                xfs_filestream_put_ag(mp, file->ag);
                xfs_filestream_get_ag(mp, dir->ag);
                *agp = file->ag = dir->ag;
            }

            xfs_mru_cache_done(cache);
        }

        /*
         * Put the file back in the cache.  If this fails, the free
         * function needs to be called to tidy up in the same way as if
         * the item had simply expired from the cache.
         */
        err = xfs_mru_cache_insert(cache, ip->i_ino, file);
        if (err) {
            xfs_fstrm_free_func(ip->i_ino, file);
            return err;
        }

        /*
         * If the file's AG was moved to the directory's new AG, there's
         * nothing more to be done.
         */
        if (*agp != NULLAGNUMBER) {
            TRACE_MOVEAG(mp, ip, pip,
                    ag, xfs_filestream_peek_ag(mp, ag),
                    *agp, xfs_filestream_peek_ag(mp, *agp));
            return 0;
        }
    }

    /*
     * If the file's parent directory is known, take its iolock in exclusive
     * mode to prevent two sibling files from racing each other to migrate
     * themselves and their parent to different AGs.
     *
     * Note that we lock the parent directory iolock inside the child
     * iolock here.  That's fine as we never hold both parent and child
     * iolock in any other place.  This is different from the ilock,
     * which requires locking of the child after the parent for namespace
     * operations.
     */
    if (pip)
        xfs_ilock(pip, XFS_IOLOCK_EXCL | XFS_IOLOCK_PARENT);

    /*
     * A new AG needs to be found for the file.  If the file's parent
     * directory is also known, it will be moved to the new AG as well to
     * ensure that files created inside it in future use the new AG.
     */
    ag = (ag == NULLAGNUMBER) ? 0 : (ag + 1) % mp->m_sb.sb_agcount;
    flags = (ap->userdata ? XFS_PICK_USERDATA : 0) |
            (ap->flist->xbf_low ? XFS_PICK_LOWSPACE : 0);

    err = _xfs_filestream_pick_ag(mp, ag, agp, flags, minlen);
    if (err || *agp == NULLAGNUMBER)
        goto exit;

    /*
     * If the file wasn't found in the file cache, then its parent directory
     * inode isn't known.  For this to have happened, the file must either
     * be pre-existing, or it was created long enough ago that its cache
     * entry has expired.  This isn't the sort of usage that the filestreams
     * allocator is trying to optimise, so there's no point trying to track
     * its new AG somehow in the filestream data structures.
     */
    if (!pip) {
        TRACE_ORPHAN(mp, ip, *agp);
        goto exit;
    }

    /* Associate the parent inode with the AG. */
    err = _xfs_filestream_update_ag(pip, NULL, *agp);
    if (err)
        goto exit;

    /* Associate the file inode with the AG. */
    err = _xfs_filestream_update_ag(ip, pip, *agp);
    if (err)
        goto exit;

    TRACE_MOVEAG(mp, ip, pip, NULLAGNUMBER, 0,
            *agp, xfs_filestream_peek_ag(mp, *agp));

exit:
    /*
     * If _xfs_filestream_pick_ag() returned a valid AG, remove the
     * reference it took on it, since the file and directory will have taken
     * their own now if they were successfully cached.
     */
    if (*agp != NULLAGNUMBER)
        xfs_filestream_put_ag(mp, *agp);
    else
        *agp = 0;

    if (pip)
        xfs_iunlock(pip, XFS_IOLOCK_EXCL);

    return err;
}

/*
 * Remove an association between an inode and a filestream object.
 * Typically this is done on last close of an unlinked file.
 */
void
xfs_filestream_deassociate(
    xfs_inode_t *ip)
{
    xfs_mru_cache_t *cache = ip->i_mount->m_filestream;

    xfs_mru_cache_delete(cache, ip->i_ino);
}