xfs: don't leak EFSBADCRC to userspace

[deliverable/linux.git] / fs / xfs / xfs_mount.c

/*
 * Copyright (c) 2000-2005 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_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_bit.h"
#include "xfs_inum.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_da_format.h"
#include "xfs_inode.h"
#include "xfs_dir2.h"
#include "xfs_ialloc.h"
#include "xfs_alloc.h"
#include "xfs_rtalloc.h"
#include "xfs_bmap.h"
#include "xfs_trans.h"
#include "xfs_trans_priv.h"
#include "xfs_log.h"
#include "xfs_error.h"
#include "xfs_quota.h"
#include "xfs_fsops.h"
#include "xfs_trace.h"
#include "xfs_icache.h"
#include "xfs_dinode.h"


#ifdef HAVE_PERCPU_SB
STATIC void     xfs_icsb_balance_counter(xfs_mount_t *, xfs_sb_field_t,
                                                int);
STATIC void     xfs_icsb_balance_counter_locked(xfs_mount_t *, xfs_sb_field_t,
                                                int);
STATIC void     xfs_icsb_disable_counter(xfs_mount_t *, xfs_sb_field_t);
#else

#define xfs_icsb_balance_counter(mp, a, b)              do { } while (0)
#define xfs_icsb_balance_counter_locked(mp, a, b)       do { } while (0)
#endif

static DEFINE_MUTEX(xfs_uuid_table_mutex);
static int xfs_uuid_table_size;
static uuid_t *xfs_uuid_table;

/*
 * See if the UUID is unique among mounted XFS filesystems.
 * Mount fails if UUID is nil or a FS with the same UUID is already mounted.
 */
STATIC int
xfs_uuid_mount(
        struct xfs_mount        *mp)
{
        uuid_t                  *uuid = &mp->m_sb.sb_uuid;
        int                     hole, i;

        if (mp->m_flags & XFS_MOUNT_NOUUID)
                return 0;

        if (uuid_is_nil(uuid)) {
                xfs_warn(mp, "Filesystem has nil UUID - can't mount");
                return XFS_ERROR(EINVAL);
        }

        mutex_lock(&xfs_uuid_table_mutex);
        for (i = 0, hole = -1; i < xfs_uuid_table_size; i++) {
                if (uuid_is_nil(&xfs_uuid_table[i])) {
                        hole = i;
                        continue;
                }
                if (uuid_equal(uuid, &xfs_uuid_table[i]))
                        goto out_duplicate;
        }

        if (hole < 0) {
                xfs_uuid_table = kmem_realloc(xfs_uuid_table,
                        (xfs_uuid_table_size + 1) * sizeof(*xfs_uuid_table),
                        xfs_uuid_table_size  * sizeof(*xfs_uuid_table),
                        KM_SLEEP);
                hole = xfs_uuid_table_size++;
        }
        xfs_uuid_table[hole] = *uuid;
        mutex_unlock(&xfs_uuid_table_mutex);

        return 0;

 out_duplicate:
        mutex_unlock(&xfs_uuid_table_mutex);
        xfs_warn(mp, "Filesystem has duplicate UUID %pU - can't mount", uuid);
        return XFS_ERROR(EINVAL);
}

STATIC void
xfs_uuid_unmount(
        struct xfs_mount        *mp)
{
        uuid_t                  *uuid = &mp->m_sb.sb_uuid;
        int                     i;

        if (mp->m_flags & XFS_MOUNT_NOUUID)
                return;

        mutex_lock(&xfs_uuid_table_mutex);
        for (i = 0; i < xfs_uuid_table_size; i++) {
                if (uuid_is_nil(&xfs_uuid_table[i]))
                        continue;
                if (!uuid_equal(uuid, &xfs_uuid_table[i]))
                        continue;
                memset(&xfs_uuid_table[i], 0, sizeof(uuid_t));
                break;
        }
        ASSERT(i < xfs_uuid_table_size);
        mutex_unlock(&xfs_uuid_table_mutex);
}


STATIC void
__xfs_free_perag(
        struct rcu_head *head)
{
        struct xfs_perag *pag = container_of(head, struct xfs_perag, rcu_head);

        ASSERT(atomic_read(&pag->pag_ref) == 0);
        kmem_free(pag);
}

/*
 * Free up the per-ag resources associated with the mount structure.
 */
STATIC void
xfs_free_perag(
        xfs_mount_t     *mp)
{
        xfs_agnumber_t  agno;
        struct xfs_perag *pag;

        for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
                spin_lock(&mp->m_perag_lock);
                pag = radix_tree_delete(&mp->m_perag_tree, agno);
                spin_unlock(&mp->m_perag_lock);
                ASSERT(pag);
                ASSERT(atomic_read(&pag->pag_ref) == 0);
                call_rcu(&pag->rcu_head, __xfs_free_perag);
        }
}

/*
 * Check size of device based on the (data/realtime) block count.
 * Note: this check is used by the growfs code as well as mount.
 */
int
xfs_sb_validate_fsb_count(
        xfs_sb_t        *sbp,
        __uint64_t      nblocks)
{
        ASSERT(PAGE_SHIFT >= sbp->sb_blocklog);
        ASSERT(sbp->sb_blocklog >= BBSHIFT);

#if XFS_BIG_BLKNOS     /* Limited by ULONG_MAX of page cache index */
        if (nblocks >> (PAGE_CACHE_SHIFT - sbp->sb_blocklog) > ULONG_MAX)
                return EFBIG;
#else                  /* Limited by UINT_MAX of sectors */
        if (nblocks << (sbp->sb_blocklog - BBSHIFT) > UINT_MAX)
                return EFBIG;
#endif
        return 0;
}

int
xfs_initialize_perag(
        xfs_mount_t     *mp,
        xfs_agnumber_t  agcount,
        xfs_agnumber_t  *maxagi)
{
        xfs_agnumber_t  index;
        xfs_agnumber_t  first_initialised = 0;
        xfs_perag_t     *pag;
        xfs_agino_t     agino;
        xfs_ino_t       ino;
        xfs_sb_t        *sbp = &mp->m_sb;
        int             error = -ENOMEM;

        /*
         * Walk the current per-ag tree so we don't try to initialise AGs
         * that already exist (growfs case). Allocate and insert all the
         * AGs we don't find ready for initialisation.
         */
        for (index = 0; index < agcount; index++) {
                pag = xfs_perag_get(mp, index);
                if (pag) {
                        xfs_perag_put(pag);
                        continue;
                }
                if (!first_initialised)
                        first_initialised = index;

                pag = kmem_zalloc(sizeof(*pag), KM_MAYFAIL);
                if (!pag)
                        goto out_unwind;
                pag->pag_agno = index;
                pag->pag_mount = mp;
                spin_lock_init(&pag->pag_ici_lock);
                mutex_init(&pag->pag_ici_reclaim_lock);
                INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC);
                spin_lock_init(&pag->pag_buf_lock);
                pag->pag_buf_tree = RB_ROOT;

                if (radix_tree_preload(GFP_NOFS))
                        goto out_unwind;

                spin_lock(&mp->m_perag_lock);
                if (radix_tree_insert(&mp->m_perag_tree, index, pag)) {
                        BUG();
                        spin_unlock(&mp->m_perag_lock);
                        radix_tree_preload_end();
                        error = -EEXIST;
                        goto out_unwind;
                }
                spin_unlock(&mp->m_perag_lock);
                radix_tree_preload_end();
        }

        /*
         * If we mount with the inode64 option, or no inode overflows
         * the legacy 32-bit address space clear the inode32 option.
         */
        agino = XFS_OFFBNO_TO_AGINO(mp, sbp->sb_agblocks - 1, 0);
        ino = XFS_AGINO_TO_INO(mp, agcount - 1, agino);

        if ((mp->m_flags & XFS_MOUNT_SMALL_INUMS) && ino > XFS_MAXINUMBER_32)
                mp->m_flags |= XFS_MOUNT_32BITINODES;
        else
                mp->m_flags &= ~XFS_MOUNT_32BITINODES;

        if (mp->m_flags & XFS_MOUNT_32BITINODES)
                index = xfs_set_inode32(mp);
        else
                index = xfs_set_inode64(mp);

        if (maxagi)
                *maxagi = index;
        return 0;

out_unwind:
        kmem_free(pag);
        for (; index > first_initialised; index--) {
                pag = radix_tree_delete(&mp->m_perag_tree, index);
                kmem_free(pag);
        }
        return error;
}

/*
 * xfs_readsb
 *
 * Does the initial read of the superblock.
 */
int
xfs_readsb(
        struct xfs_mount *mp,
        int             flags)
{
        unsigned int    sector_size;
        struct xfs_buf  *bp;
        struct xfs_sb   *sbp = &mp->m_sb;
        int             error;
        int             loud = !(flags & XFS_MFSI_QUIET);

        ASSERT(mp->m_sb_bp == NULL);
        ASSERT(mp->m_ddev_targp != NULL);

        /*
         * Allocate a (locked) buffer to hold the superblock.
         * This will be kept around at all times to optimize
         * access to the superblock.
         */
        sector_size = xfs_getsize_buftarg(mp->m_ddev_targp);

reread:
        bp = xfs_buf_read_uncached(mp->m_ddev_targp, XFS_SB_DADDR,
                                   BTOBB(sector_size), 0,
                                   loud ? &xfs_sb_buf_ops
                                        : &xfs_sb_quiet_buf_ops);
        if (!bp) {
                if (loud)
                        xfs_warn(mp, "SB buffer read failed");
                return EIO;
        }
        if (bp->b_error) {
                error = bp->b_error;
                if (loud)
                        xfs_warn(mp, "SB validate failed with error %d.", error);
                /* bad CRC means corrupted metadata */
                if (error == EFSBADCRC)
                        error = EFSCORRUPTED;
                goto release_buf;
        }

        /*
         * Initialize the mount structure from the superblock.
         */
        xfs_sb_from_disk(&mp->m_sb, XFS_BUF_TO_SBP(bp));
        xfs_sb_quota_from_disk(&mp->m_sb);

        /*
         * We must be able to do sector-sized and sector-aligned IO.
         */
        if (sector_size > sbp->sb_sectsize) {
                if (loud)
                        xfs_warn(mp, "device supports %u byte sectors (not %u)",
                                sector_size, sbp->sb_sectsize);
                error = ENOSYS;
                goto release_buf;
        }

        /*
         * If device sector size is smaller than the superblock size,
         * re-read the superblock so the buffer is correctly sized.
         */
        if (sector_size < sbp->sb_sectsize) {
                xfs_buf_relse(bp);
                sector_size = sbp->sb_sectsize;
                goto reread;
        }

        /* Initialize per-cpu counters */
        xfs_icsb_reinit_counters(mp);

        /* no need to be quiet anymore, so reset the buf ops */
        bp->b_ops = &xfs_sb_buf_ops;

        mp->m_sb_bp = bp;
        xfs_buf_unlock(bp);
        return 0;

release_buf:
        xfs_buf_relse(bp);
        return error;
}

/*
 * Update alignment values based on mount options and sb values
 */
STATIC int
xfs_update_alignment(xfs_mount_t *mp)
{
        xfs_sb_t        *sbp = &(mp->m_sb);

        if (mp->m_dalign) {
                /*
                 * If stripe unit and stripe width are not multiples
                 * of the fs blocksize turn off alignment.
                 */
                if ((BBTOB(mp->m_dalign) & mp->m_blockmask) ||
                    (BBTOB(mp->m_swidth) & mp->m_blockmask)) {
                        xfs_warn(mp,
                "alignment check failed: sunit/swidth vs. blocksize(%d)",
                                sbp->sb_blocksize);
                        return XFS_ERROR(EINVAL);
                } else {
                        /*
                         * Convert the stripe unit and width to FSBs.
                         */
                        mp->m_dalign = XFS_BB_TO_FSBT(mp, mp->m_dalign);
                        if (mp->m_dalign && (sbp->sb_agblocks % mp->m_dalign)) {
                                xfs_warn(mp,
                        "alignment check failed: sunit/swidth vs. agsize(%d)",
                                         sbp->sb_agblocks);
                                return XFS_ERROR(EINVAL);
                        } else if (mp->m_dalign) {
                                mp->m_swidth = XFS_BB_TO_FSBT(mp, mp->m_swidth);
                        } else {
                                xfs_warn(mp,
                        "alignment check failed: sunit(%d) less than bsize(%d)",
                                         mp->m_dalign, sbp->sb_blocksize);
                                return XFS_ERROR(EINVAL);
                        }
                }

                /*
                 * Update superblock with new values
                 * and log changes
                 */
                if (xfs_sb_version_hasdalign(sbp)) {
                        if (sbp->sb_unit != mp->m_dalign) {
                                sbp->sb_unit = mp->m_dalign;
                                mp->m_update_flags |= XFS_SB_UNIT;
                        }
                        if (sbp->sb_width != mp->m_swidth) {
                                sbp->sb_width = mp->m_swidth;
                                mp->m_update_flags |= XFS_SB_WIDTH;
                        }
                } else {
                        xfs_warn(mp,
        "cannot change alignment: superblock does not support data alignment");
                        return XFS_ERROR(EINVAL);
                }
        } else if ((mp->m_flags & XFS_MOUNT_NOALIGN) != XFS_MOUNT_NOALIGN &&
                    xfs_sb_version_hasdalign(&mp->m_sb)) {
                        mp->m_dalign = sbp->sb_unit;
                        mp->m_swidth = sbp->sb_width;
        }

        return 0;
}

/*
 * Set the maximum inode count for this filesystem
 */
STATIC void
xfs_set_maxicount(xfs_mount_t *mp)
{
        xfs_sb_t        *sbp = &(mp->m_sb);
        __uint64_t      icount;

        if (sbp->sb_imax_pct) {
                /*
                 * Make sure the maximum inode count is a multiple
                 * of the units we allocate inodes in.
                 */
                icount = sbp->sb_dblocks * sbp->sb_imax_pct;
                do_div(icount, 100);
                do_div(icount, mp->m_ialloc_blks);
                mp->m_maxicount = (icount * mp->m_ialloc_blks)  <<
                                   sbp->sb_inopblog;
        } else {
                mp->m_maxicount = 0;
        }
}

/*
 * Set the default minimum read and write sizes unless
 * already specified in a mount option.
 * We use smaller I/O sizes when the file system
 * is being used for NFS service (wsync mount option).
 */
STATIC void
xfs_set_rw_sizes(xfs_mount_t *mp)
{
        xfs_sb_t        *sbp = &(mp->m_sb);
        int             readio_log, writeio_log;

        if (!(mp->m_flags & XFS_MOUNT_DFLT_IOSIZE)) {
                if (mp->m_flags & XFS_MOUNT_WSYNC) {
                        readio_log = XFS_WSYNC_READIO_LOG;
                        writeio_log = XFS_WSYNC_WRITEIO_LOG;
                } else {
                        readio_log = XFS_READIO_LOG_LARGE;
                        writeio_log = XFS_WRITEIO_LOG_LARGE;
                }
        } else {
                readio_log = mp->m_readio_log;
                writeio_log = mp->m_writeio_log;
        }

        if (sbp->sb_blocklog > readio_log) {
                mp->m_readio_log = sbp->sb_blocklog;
        } else {
                mp->m_readio_log = readio_log;
        }
        mp->m_readio_blocks = 1 << (mp->m_readio_log - sbp->sb_blocklog);
        if (sbp->sb_blocklog > writeio_log) {
                mp->m_writeio_log = sbp->sb_blocklog;
        } else {
                mp->m_writeio_log = writeio_log;
        }
        mp->m_writeio_blocks = 1 << (mp->m_writeio_log - sbp->sb_blocklog);
}

/*
 * precalculate the low space thresholds for dynamic speculative preallocation.
 */
void
xfs_set_low_space_thresholds(
        struct xfs_mount        *mp)
{
        int i;

        for (i = 0; i < XFS_LOWSP_MAX; i++) {
                __uint64_t space = mp->m_sb.sb_dblocks;

                do_div(space, 100);
                mp->m_low_space[i] = space * (i + 1);
        }
}


/*
 * Set whether we're using inode alignment.
 */
STATIC void
xfs_set_inoalignment(xfs_mount_t *mp)
{
        if (xfs_sb_version_hasalign(&mp->m_sb) &&
            mp->m_sb.sb_inoalignmt >=
            XFS_B_TO_FSBT(mp, mp->m_inode_cluster_size))
                mp->m_inoalign_mask = mp->m_sb.sb_inoalignmt - 1;
        else
                mp->m_inoalign_mask = 0;
        /*
         * If we are using stripe alignment, check whether
         * the stripe unit is a multiple of the inode alignment
         */
        if (mp->m_dalign && mp->m_inoalign_mask &&
            !(mp->m_dalign & mp->m_inoalign_mask))
                mp->m_sinoalign = mp->m_dalign;
        else
                mp->m_sinoalign = 0;
}

/*
 * Check that the data (and log if separate) is an ok size.
 */
STATIC int
xfs_check_sizes(xfs_mount_t *mp)
{
        xfs_buf_t       *bp;
        xfs_daddr_t     d;

        d = (xfs_daddr_t)XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks);
        if (XFS_BB_TO_FSB(mp, d) != mp->m_sb.sb_dblocks) {
                xfs_warn(mp, "filesystem size mismatch detected");
                return XFS_ERROR(EFBIG);
        }
        bp = xfs_buf_read_uncached(mp->m_ddev_targp,
                                        d - XFS_FSS_TO_BB(mp, 1),
                                        XFS_FSS_TO_BB(mp, 1), 0, NULL);
        if (!bp) {
                xfs_warn(mp, "last sector read failed");
                return EIO;
        }
        xfs_buf_relse(bp);

        if (mp->m_logdev_targp != mp->m_ddev_targp) {
                d = (xfs_daddr_t)XFS_FSB_TO_BB(mp, mp->m_sb.sb_logblocks);
                if (XFS_BB_TO_FSB(mp, d) != mp->m_sb.sb_logblocks) {
                        xfs_warn(mp, "log size mismatch detected");
                        return XFS_ERROR(EFBIG);
                }
                bp = xfs_buf_read_uncached(mp->m_logdev_targp,
                                        d - XFS_FSB_TO_BB(mp, 1),
                                        XFS_FSB_TO_BB(mp, 1), 0, NULL);
                if (!bp) {
                        xfs_warn(mp, "log device read failed");
                        return EIO;
                }
                xfs_buf_relse(bp);
        }
        return 0;
}

/*
 * Clear the quotaflags in memory and in the superblock.
 */
int
xfs_mount_reset_sbqflags(
        struct xfs_mount        *mp)
{
        int                     error;
        struct xfs_trans        *tp;

        mp->m_qflags = 0;

        /*
         * It is OK to look at sb_qflags here in mount path,
         * without m_sb_lock.
         */
        if (mp->m_sb.sb_qflags == 0)
                return 0;
        spin_lock(&mp->m_sb_lock);
        mp->m_sb.sb_qflags = 0;
        spin_unlock(&mp->m_sb_lock);

        /*
         * If the fs is readonly, let the incore superblock run
         * with quotas off but don't flush the update out to disk
         */
        if (mp->m_flags & XFS_MOUNT_RDONLY)
                return 0;

        tp = xfs_trans_alloc(mp, XFS_TRANS_QM_SBCHANGE);
        error = xfs_trans_reserve(tp, &M_RES(mp)->tr_qm_sbchange, 0, 0);
        if (error) {
                xfs_trans_cancel(tp, 0);
                xfs_alert(mp, "%s: Superblock update failed!", __func__);
                return error;
        }

        xfs_mod_sb(tp, XFS_SB_QFLAGS);
        return xfs_trans_commit(tp, 0);
}

__uint64_t
xfs_default_resblks(xfs_mount_t *mp)
{
        __uint64_t resblks;

        /*
         * We default to 5% or 8192 fsbs of space reserved, whichever is
         * smaller.  This is intended to cover concurrent allocation
         * transactions when we initially hit enospc. These each require a 4
         * block reservation. Hence by default we cover roughly 2000 concurrent
         * allocation reservations.
         */
        resblks = mp->m_sb.sb_dblocks;
        do_div(resblks, 20);
        resblks = min_t(__uint64_t, resblks, 8192);
        return resblks;
}

/*
 * This function does the following on an initial mount of a file system:
 *      - reads the superblock from disk and init the mount struct
 *      - if we're a 32-bit kernel, do a size check on the superblock
 *              so we don't mount terabyte filesystems
 *      - init mount struct realtime fields
 *      - allocate inode hash table for fs
 *      - init directory manager
 *      - perform recovery and init the log manager
 */
int
xfs_mountfs(
        xfs_mount_t     *mp)
{
        xfs_sb_t        *sbp = &(mp->m_sb);
        xfs_inode_t     *rip;
        __uint64_t      resblks;
        uint            quotamount = 0;
        uint            quotaflags = 0;
        int             error = 0;

        xfs_sb_mount_common(mp, sbp);

        /*
         * Check for a mismatched features2 values.  Older kernels
         * read & wrote into the wrong sb offset for sb_features2
         * on some platforms due to xfs_sb_t not being 64bit size aligned
         * when sb_features2 was added, which made older superblock
         * reading/writing routines swap it as a 64-bit value.
         *
         * For backwards compatibility, we make both slots equal.
         *
         * If we detect a mismatched field, we OR the set bits into the
         * existing features2 field in case it has already been modified; we
         * don't want to lose any features.  We then update the bad location
         * with the ORed value so that older kernels will see any features2
         * flags, and mark the two fields as needing updates once the
         * transaction subsystem is online.
         */
        if (xfs_sb_has_mismatched_features2(sbp)) {
                xfs_warn(mp, "correcting sb_features alignment problem");
                sbp->sb_features2 |= sbp->sb_bad_features2;
                sbp->sb_bad_features2 = sbp->sb_features2;
                mp->m_update_flags |= XFS_SB_FEATURES2 | XFS_SB_BAD_FEATURES2;

                /*
                 * Re-check for ATTR2 in case it was found in bad_features2
                 * slot.
                 */
                if (xfs_sb_version_hasattr2(&mp->m_sb) &&
                   !(mp->m_flags & XFS_MOUNT_NOATTR2))
                        mp->m_flags |= XFS_MOUNT_ATTR2;
        }

        if (xfs_sb_version_hasattr2(&mp->m_sb) &&
           (mp->m_flags & XFS_MOUNT_NOATTR2)) {
                xfs_sb_version_removeattr2(&mp->m_sb);
                mp->m_update_flags |= XFS_SB_FEATURES2;

                /* update sb_versionnum for the clearing of the morebits */
                if (!sbp->sb_features2)
                        mp->m_update_flags |= XFS_SB_VERSIONNUM;
        }

        /*
         * Check if sb_agblocks is aligned at stripe boundary
         * If sb_agblocks is NOT aligned turn off m_dalign since
         * allocator alignment is within an ag, therefore ag has
         * to be aligned at stripe boundary.
         */
        error = xfs_update_alignment(mp);
        if (error)
                goto out;

        xfs_alloc_compute_maxlevels(mp);
        xfs_bmap_compute_maxlevels(mp, XFS_DATA_FORK);
        xfs_bmap_compute_maxlevels(mp, XFS_ATTR_FORK);
        xfs_ialloc_compute_maxlevels(mp);

        xfs_set_maxicount(mp);

        error = xfs_uuid_mount(mp);
        if (error)
                goto out;

        /*
         * Set the minimum read and write sizes
         */
        xfs_set_rw_sizes(mp);

        /* set the low space thresholds for dynamic preallocation */
        xfs_set_low_space_thresholds(mp);

        /*
         * Set the inode cluster size.
         * This may still be overridden by the file system
         * block size if it is larger than the chosen cluster size.
         *
         * For v5 filesystems, scale the cluster size with the inode size to
         * keep a constant ratio of inode per cluster buffer, but only if mkfs
         * has set the inode alignment value appropriately for larger cluster
         * sizes.
         */
        mp->m_inode_cluster_size = XFS_INODE_BIG_CLUSTER_SIZE;
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                int     new_size = mp->m_inode_cluster_size;

                new_size *= mp->m_sb.sb_inodesize / XFS_DINODE_MIN_SIZE;
                if (mp->m_sb.sb_inoalignmt >= XFS_B_TO_FSBT(mp, new_size))
                        mp->m_inode_cluster_size = new_size;
                xfs_info(mp, "Using inode cluster size of %d bytes",
                         mp->m_inode_cluster_size);
        }

        /*
         * Set inode alignment fields
         */
        xfs_set_inoalignment(mp);

        /*
         * Check that the data (and log if separate) is an ok size.
         */
        error = xfs_check_sizes(mp);
        if (error)
                goto out_remove_uuid;

        /*
         * Initialize realtime fields in the mount structure
         */
        error = xfs_rtmount_init(mp);
        if (error) {
                xfs_warn(mp, "RT mount failed");
                goto out_remove_uuid;
        }

        /*
         *  Copies the low order bits of the timestamp and the randomly
         *  set "sequence" number out of a UUID.
         */
        uuid_getnodeuniq(&sbp->sb_uuid, mp->m_fixedfsid);

        mp->m_dmevmask = 0;     /* not persistent; set after each mount */

        xfs_dir_mount(mp);

        /*
         * Initialize the attribute manager's entries.
         */
        mp->m_attr_magicpct = (mp->m_sb.sb_blocksize * 37) / 100;

        /*
         * Initialize the precomputed transaction reservations values.
         */
        xfs_trans_init(mp);

        /*
         * Allocate and initialize the per-ag data.
         */
        spin_lock_init(&mp->m_perag_lock);
        INIT_RADIX_TREE(&mp->m_perag_tree, GFP_ATOMIC);
        error = xfs_initialize_perag(mp, sbp->sb_agcount, &mp->m_maxagi);
        if (error) {
                xfs_warn(mp, "Failed per-ag init: %d", error);
                goto out_remove_uuid;
        }

        if (!sbp->sb_logblocks) {
                xfs_warn(mp, "no log defined");
                XFS_ERROR_REPORT("xfs_mountfs", XFS_ERRLEVEL_LOW, mp);
                error = XFS_ERROR(EFSCORRUPTED);
                goto out_free_perag;
        }

        /*
         * log's mount-time initialization. Perform 1st part recovery if needed
         */
        error = xfs_log_mount(mp, mp->m_logdev_targp,
                              XFS_FSB_TO_DADDR(mp, sbp->sb_logstart),
                              XFS_FSB_TO_BB(mp, sbp->sb_logblocks));
        if (error) {
                xfs_warn(mp, "log mount failed");
                goto out_fail_wait;
        }

        /*
         * Now the log is mounted, we know if it was an unclean shutdown or
         * not. If it was, with the first phase of recovery has completed, we
         * have consistent AG blocks on disk. We have not recovered EFIs yet,
         * but they are recovered transactionally in the second recovery phase
         * later.
         *
         * Hence we can safely re-initialise incore superblock counters from
         * the per-ag data. These may not be correct if the filesystem was not
         * cleanly unmounted, so we need to wait for recovery to finish before
         * doing this.
         *
         * If the filesystem was cleanly unmounted, then we can trust the
         * values in the superblock to be correct and we don't need to do
         * anything here.
         *
         * If we are currently making the filesystem, the initialisation will
         * fail as the perag data is in an undefined state.
         */
        if (xfs_sb_version_haslazysbcount(&mp->m_sb) &&
            !XFS_LAST_UNMOUNT_WAS_CLEAN(mp) &&
             !mp->m_sb.sb_inprogress) {
                error = xfs_initialize_perag_data(mp, sbp->sb_agcount);
                if (error)
                        goto out_fail_wait;
        }

        /*
         * Get and sanity-check the root inode.
         * Save the pointer to it in the mount structure.
         */
        error = xfs_iget(mp, NULL, sbp->sb_rootino, 0, XFS_ILOCK_EXCL, &rip);
        if (error) {
                xfs_warn(mp, "failed to read root inode");
                goto out_log_dealloc;
        }

        ASSERT(rip != NULL);

        if (unlikely(!S_ISDIR(rip->i_d.di_mode))) {
                xfs_warn(mp, "corrupted root inode %llu: not a directory",
                        (unsigned long long)rip->i_ino);
                xfs_iunlock(rip, XFS_ILOCK_EXCL);
                XFS_ERROR_REPORT("xfs_mountfs_int(2)", XFS_ERRLEVEL_LOW,
                                 mp);
                error = XFS_ERROR(EFSCORRUPTED);
                goto out_rele_rip;
        }
        mp->m_rootip = rip;     /* save it */

        xfs_iunlock(rip, XFS_ILOCK_EXCL);

        /*
         * Initialize realtime inode pointers in the mount structure
         */
        error = xfs_rtmount_inodes(mp);
        if (error) {
                /*
                 * Free up the root inode.
                 */
                xfs_warn(mp, "failed to read RT inodes");
                goto out_rele_rip;
        }

        /*
         * If this is a read-only mount defer the superblock updates until
         * the next remount into writeable mode.  Otherwise we would never
         * perform the update e.g. for the root filesystem.
         */
        if (mp->m_update_flags && !(mp->m_flags & XFS_MOUNT_RDONLY)) {
                error = xfs_mount_log_sb(mp, mp->m_update_flags);
                if (error) {
                        xfs_warn(mp, "failed to write sb changes");
                        goto out_rtunmount;
                }
        }

        /*
         * Initialise the XFS quota management subsystem for this mount
         */
        if (XFS_IS_QUOTA_RUNNING(mp)) {
                error = xfs_qm_newmount(mp, &quotamount, &quotaflags);
                if (error)
                        goto out_rtunmount;
        } else {
                ASSERT(!XFS_IS_QUOTA_ON(mp));

                /*
                 * If a file system had quotas running earlier, but decided to
                 * mount without -o uquota/pquota/gquota options, revoke the
                 * quotachecked license.
                 */
                if (mp->m_sb.sb_qflags & XFS_ALL_QUOTA_ACCT) {
                        xfs_notice(mp, "resetting quota flags");
                        error = xfs_mount_reset_sbqflags(mp);
                        if (error)
                                return error;
                }
        }

        /*
         * Finish recovering the file system.  This part needed to be
         * delayed until after the root and real-time bitmap inodes
         * were consistently read in.
         */
        error = xfs_log_mount_finish(mp);
        if (error) {
                xfs_warn(mp, "log mount finish failed");
                goto out_rtunmount;
        }

        /*
         * Complete the quota initialisation, post-log-replay component.
         */
        if (quotamount) {
                ASSERT(mp->m_qflags == 0);
                mp->m_qflags = quotaflags;

                xfs_qm_mount_quotas(mp);
        }

        /*
         * Now we are mounted, reserve a small amount of unused space for
         * privileged transactions. This is needed so that transaction
         * space required for critical operations can dip into this pool
         * when at ENOSPC. This is needed for operations like create with
         * attr, unwritten extent conversion at ENOSPC, etc. Data allocations
         * are not allowed to use this reserved space.
         *
         * This may drive us straight to ENOSPC on mount, but that implies
         * we were already there on the last unmount. Warn if this occurs.
         */
        if (!(mp->m_flags & XFS_MOUNT_RDONLY)) {
                resblks = xfs_default_resblks(mp);
                error = xfs_reserve_blocks(mp, &resblks, NULL);
                if (error)
                        xfs_warn(mp,
        "Unable to allocate reserve blocks. Continuing without reserve pool.");
        }

        return 0;

 out_rtunmount:
        xfs_rtunmount_inodes(mp);
 out_rele_rip:
        IRELE(rip);
 out_log_dealloc:
        xfs_log_unmount(mp);
 out_fail_wait:
        if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp)
                xfs_wait_buftarg(mp->m_logdev_targp);
        xfs_wait_buftarg(mp->m_ddev_targp);
 out_free_perag:
        xfs_free_perag(mp);
 out_remove_uuid:
        xfs_uuid_unmount(mp);
 out:
        return error;
}

/*
 * This flushes out the inodes,dquots and the superblock, unmounts the
 * log and makes sure that incore structures are freed.
 */
void
xfs_unmountfs(
        struct xfs_mount        *mp)
{
        __uint64_t              resblks;
        int                     error;

        cancel_delayed_work_sync(&mp->m_eofblocks_work);

        xfs_qm_unmount_quotas(mp);
        xfs_rtunmount_inodes(mp);
        IRELE(mp->m_rootip);

        /*
         * We can potentially deadlock here if we have an inode cluster
         * that has been freed has its buffer still pinned in memory because
         * the transaction is still sitting in a iclog. The stale inodes
         * on that buffer will have their flush locks held until the
         * transaction hits the disk and the callbacks run. the inode
         * flush takes the flush lock unconditionally and with nothing to
         * push out the iclog we will never get that unlocked. hence we
         * need to force the log first.
         */
        xfs_log_force(mp, XFS_LOG_SYNC);

        /*
         * Flush all pending changes from the AIL.
         */
        xfs_ail_push_all_sync(mp->m_ail);

        /*
         * And reclaim all inodes.  At this point there should be no dirty
         * inodes and none should be pinned or locked, but use synchronous
         * reclaim just to be sure. We can stop background inode reclaim
         * here as well if it is still running.
         */
        cancel_delayed_work_sync(&mp->m_reclaim_work);
        xfs_reclaim_inodes(mp, SYNC_WAIT);

        xfs_qm_unmount(mp);

        /*
         * Unreserve any blocks we have so that when we unmount we don't account
         * the reserved free space as used. This is really only necessary for
         * lazy superblock counting because it trusts the incore superblock
         * counters to be absolutely correct on clean unmount.
         *
         * We don't bother correcting this elsewhere for lazy superblock
         * counting because on mount of an unclean filesystem we reconstruct the
         * correct counter value and this is irrelevant.
         *
         * For non-lazy counter filesystems, this doesn't matter at all because
         * we only every apply deltas to the superblock and hence the incore
         * value does not matter....
         */
        resblks = 0;
        error = xfs_reserve_blocks(mp, &resblks, NULL);
        if (error)
                xfs_warn(mp, "Unable to free reserved block pool. "
                                "Freespace may not be correct on next mount.");

        error = xfs_log_sbcount(mp);
        if (error)
                xfs_warn(mp, "Unable to update superblock counters. "
                                "Freespace may not be correct on next mount.");

        xfs_log_unmount(mp);
        xfs_uuid_unmount(mp);

#if defined(DEBUG)
        xfs_errortag_clearall(mp, 0);
#endif
        xfs_free_perag(mp);
}

int
xfs_fs_writable(xfs_mount_t *mp)
{
        return !(mp->m_super->s_writers.frozen || XFS_FORCED_SHUTDOWN(mp) ||
                (mp->m_flags & XFS_MOUNT_RDONLY));
}

/*
 * xfs_log_sbcount
 *
 * Sync the superblock counters to disk.
 *
 * Note this code can be called during the process of freezing, so
 * we may need to use the transaction allocator which does not
 * block when the transaction subsystem is in its frozen state.
 */
int
xfs_log_sbcount(xfs_mount_t *mp)
{
        xfs_trans_t     *tp;
        int             error;

        if (!xfs_fs_writable(mp))
                return 0;

        xfs_icsb_sync_counters(mp, 0);

        /*
         * we don't need to do this if we are updating the superblock
         * counters on every modification.
         */
        if (!xfs_sb_version_haslazysbcount(&mp->m_sb))
                return 0;

        tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP);
        error = xfs_trans_reserve(tp, &M_RES(mp)->tr_sb, 0, 0);
        if (error) {
                xfs_trans_cancel(tp, 0);
                return error;
        }

        xfs_mod_sb(tp, XFS_SB_IFREE | XFS_SB_ICOUNT | XFS_SB_FDBLOCKS);
        xfs_trans_set_sync(tp);
        error = xfs_trans_commit(tp, 0);
        return error;
}

/*
 * xfs_mod_incore_sb_unlocked() is a utility routine commonly used to apply
 * a delta to a specified field in the in-core superblock.  Simply
 * switch on the field indicated and apply the delta to that field.
 * Fields are not allowed to dip below zero, so if the delta would
 * do this do not apply it and return EINVAL.
 *
 * The m_sb_lock must be held when this routine is called.
 */
STATIC int
xfs_mod_incore_sb_unlocked(
        xfs_mount_t     *mp,
        xfs_sb_field_t  field,
        int64_t         delta,
        int             rsvd)
{
        int             scounter;       /* short counter for 32 bit fields */
        long long       lcounter;       /* long counter for 64 bit fields */
        long long       res_used, rem;

        /*
         * With the in-core superblock spin lock held, switch
         * on the indicated field.  Apply the delta to the
         * proper field.  If the fields value would dip below
         * 0, then do not apply the delta and return EINVAL.
         */
        switch (field) {
        case XFS_SBS_ICOUNT:
                lcounter = (long long)mp->m_sb.sb_icount;
                lcounter += delta;
                if (lcounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_icount = lcounter;
                return 0;
        case XFS_SBS_IFREE:
                lcounter = (long long)mp->m_sb.sb_ifree;
                lcounter += delta;
                if (lcounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_ifree = lcounter;
                return 0;
        case XFS_SBS_FDBLOCKS:
                lcounter = (long long)
                        mp->m_sb.sb_fdblocks - XFS_ALLOC_SET_ASIDE(mp);
                res_used = (long long)(mp->m_resblks - mp->m_resblks_avail);

                if (delta > 0) {                /* Putting blocks back */
                        if (res_used > delta) {
                                mp->m_resblks_avail += delta;
                        } else {
                                rem = delta - res_used;
                                mp->m_resblks_avail = mp->m_resblks;
                                lcounter += rem;
                        }
                } else {                                /* Taking blocks away */
                        lcounter += delta;
                        if (lcounter >= 0) {
                                mp->m_sb.sb_fdblocks = lcounter +
                                                        XFS_ALLOC_SET_ASIDE(mp);
                                return 0;
                        }

                        /*
                         * We are out of blocks, use any available reserved
                         * blocks if were allowed to.
                         */
                        if (!rsvd)
                                return XFS_ERROR(ENOSPC);

                        lcounter = (long long)mp->m_resblks_avail + delta;
                        if (lcounter >= 0) {
                                mp->m_resblks_avail = lcounter;
                                return 0;
                        }
                        printk_once(KERN_WARNING
                                "Filesystem \"%s\": reserve blocks depleted! "
                                "Consider increasing reserve pool size.",
                                mp->m_fsname);
                        return XFS_ERROR(ENOSPC);
                }

                mp->m_sb.sb_fdblocks = lcounter + XFS_ALLOC_SET_ASIDE(mp);
                return 0;
        case XFS_SBS_FREXTENTS:
                lcounter = (long long)mp->m_sb.sb_frextents;
                lcounter += delta;
                if (lcounter < 0) {
                        return XFS_ERROR(ENOSPC);
                }
                mp->m_sb.sb_frextents = lcounter;
                return 0;
        case XFS_SBS_DBLOCKS:
                lcounter = (long long)mp->m_sb.sb_dblocks;
                lcounter += delta;
                if (lcounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_dblocks = lcounter;
                return 0;
        case XFS_SBS_AGCOUNT:
                scounter = mp->m_sb.sb_agcount;
                scounter += delta;
                if (scounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_agcount = scounter;
                return 0;
        case XFS_SBS_IMAX_PCT:
                scounter = mp->m_sb.sb_imax_pct;
                scounter += delta;
                if (scounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_imax_pct = scounter;
                return 0;
        case XFS_SBS_REXTSIZE:
                scounter = mp->m_sb.sb_rextsize;
                scounter += delta;
                if (scounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_rextsize = scounter;
                return 0;
        case XFS_SBS_RBMBLOCKS:
                scounter = mp->m_sb.sb_rbmblocks;
                scounter += delta;
                if (scounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_rbmblocks = scounter;
                return 0;
        case XFS_SBS_RBLOCKS:
                lcounter = (long long)mp->m_sb.sb_rblocks;
                lcounter += delta;
                if (lcounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_rblocks = lcounter;
                return 0;
        case XFS_SBS_REXTENTS:
                lcounter = (long long)mp->m_sb.sb_rextents;
                lcounter += delta;
                if (lcounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_rextents = lcounter;
                return 0;
        case XFS_SBS_REXTSLOG:
                scounter = mp->m_sb.sb_rextslog;
                scounter += delta;
                if (scounter < 0) {
                        ASSERT(0);
                        return XFS_ERROR(EINVAL);
                }
                mp->m_sb.sb_rextslog = scounter;
                return 0;
        default:
                ASSERT(0);
                return XFS_ERROR(EINVAL);
        }
}

/*
 * xfs_mod_incore_sb() is used to change a field in the in-core
 * superblock structure by the specified delta.  This modification
 * is protected by the m_sb_lock.  Just use the xfs_mod_incore_sb_unlocked()
 * routine to do the work.
 */
int
xfs_mod_incore_sb(
        struct xfs_mount        *mp,
        xfs_sb_field_t          field,
        int64_t                 delta,
        int                     rsvd)
{
        int                     status;

#ifdef HAVE_PERCPU_SB
        ASSERT(field < XFS_SBS_ICOUNT || field > XFS_SBS_FDBLOCKS);
#endif
        spin_lock(&mp->m_sb_lock);
        status = xfs_mod_incore_sb_unlocked(mp, field, delta, rsvd);
        spin_unlock(&mp->m_sb_lock);

        return status;
}

/*
 * Change more than one field in the in-core superblock structure at a time.
 *
 * The fields and changes to those fields are specified in the array of
 * xfs_mod_sb structures passed in.  Either all of the specified deltas
 * will be applied or none of them will.  If any modified field dips below 0,
 * then all modifications will be backed out and EINVAL will be returned.
 *
 * Note that this function may not be used for the superblock values that
 * are tracked with the in-memory per-cpu counters - a direct call to
 * xfs_icsb_modify_counters is required for these.
 */
int
xfs_mod_incore_sb_batch(
        struct xfs_mount        *mp,
        xfs_mod_sb_t            *msb,
        uint                    nmsb,
        int                     rsvd)
{
        xfs_mod_sb_t            *msbp;
        int                     error = 0;

        /*
         * Loop through the array of mod structures and apply each individually.
         * If any fail, then back out all those which have already been applied.
         * Do all of this within the scope of the m_sb_lock so that all of the
         * changes will be atomic.
         */
        spin_lock(&mp->m_sb_lock);
        for (msbp = msb; msbp < (msb + nmsb); msbp++) {
                ASSERT(msbp->msb_field < XFS_SBS_ICOUNT ||
                       msbp->msb_field > XFS_SBS_FDBLOCKS);

                error = xfs_mod_incore_sb_unlocked(mp, msbp->msb_field,
                                                   msbp->msb_delta, rsvd);
                if (error)
                        goto unwind;
        }
        spin_unlock(&mp->m_sb_lock);
        return 0;

unwind:
        while (--msbp >= msb) {
                error = xfs_mod_incore_sb_unlocked(mp, msbp->msb_field,
                                                   -msbp->msb_delta, rsvd);
                ASSERT(error == 0);
        }
        spin_unlock(&mp->m_sb_lock);
        return error;
}

/*
 * xfs_getsb() is called to obtain the buffer for the superblock.
 * The buffer is returned locked and read in from disk.
 * The buffer should be released with a call to xfs_brelse().
 *
 * If the flags parameter is BUF_TRYLOCK, then we'll only return
 * the superblock buffer if it can be locked without sleeping.
 * If it can't then we'll return NULL.
 */
struct xfs_buf *
xfs_getsb(
        struct xfs_mount        *mp,
        int                     flags)
{
        struct xfs_buf          *bp = mp->m_sb_bp;

        if (!xfs_buf_trylock(bp)) {
                if (flags & XBF_TRYLOCK)
                        return NULL;
                xfs_buf_lock(bp);
        }

        xfs_buf_hold(bp);
        ASSERT(XFS_BUF_ISDONE(bp));
        return bp;
}

/*
 * Used to free the superblock along various error paths.
 */
void
xfs_freesb(
        struct xfs_mount        *mp)
{
        struct xfs_buf          *bp = mp->m_sb_bp;

        xfs_buf_lock(bp);
        mp->m_sb_bp = NULL;
        xfs_buf_relse(bp);
}

/*
 * Used to log changes to the superblock unit and width fields which could
 * be altered by the mount options, as well as any potential sb_features2
 * fixup. Only the first superblock is updated.
 */
int
xfs_mount_log_sb(
        xfs_mount_t     *mp,
        __int64_t       fields)
{
        xfs_trans_t     *tp;
        int             error;

        ASSERT(fields & (XFS_SB_UNIT | XFS_SB_WIDTH | XFS_SB_UUID |
                         XFS_SB_FEATURES2 | XFS_SB_BAD_FEATURES2 |
                         XFS_SB_VERSIONNUM));

        tp = xfs_trans_alloc(mp, XFS_TRANS_SB_UNIT);
        error = xfs_trans_reserve(tp, &M_RES(mp)->tr_sb, 0, 0);
        if (error) {
                xfs_trans_cancel(tp, 0);
                return error;
        }
        xfs_mod_sb(tp, fields);
        error = xfs_trans_commit(tp, 0);
        return error;
}

/*
 * If the underlying (data/log/rt) device is readonly, there are some
 * operations that cannot proceed.
 */
int
xfs_dev_is_read_only(
        struct xfs_mount        *mp,
        char                    *message)
{
        if (xfs_readonly_buftarg(mp->m_ddev_targp) ||
            xfs_readonly_buftarg(mp->m_logdev_targp) ||
            (mp->m_rtdev_targp && xfs_readonly_buftarg(mp->m_rtdev_targp))) {
                xfs_notice(mp, "%s required on read-only device.", message);
                xfs_notice(mp, "write access unavailable, cannot proceed.");
                return EROFS;
        }
        return 0;
}

#ifdef HAVE_PERCPU_SB
/*
 * Per-cpu incore superblock counters
 *
 * Simple concept, difficult implementation
 *
 * Basically, replace the incore superblock counters with a distributed per cpu
 * counter for contended fields (e.g.  free block count).
 *
 * Difficulties arise in that the incore sb is used for ENOSPC checking, and
 * hence needs to be accurately read when we are running low on space. Hence
 * there is a method to enable and disable the per-cpu counters based on how
 * much "stuff" is available in them.
 *
 * Basically, a counter is enabled if there is enough free resource to justify
 * running a per-cpu fast-path. If the per-cpu counter runs out (i.e. a local
 * ENOSPC), then we disable the counters to synchronise all callers and
 * re-distribute the available resources.
 *
 * If, once we redistributed the available resources, we still get a failure,
 * we disable the per-cpu counter and go through the slow path.
 *
 * The slow path is the current xfs_mod_incore_sb() function.  This means that
 * when we disable a per-cpu counter, we need to drain its resources back to
 * the global superblock. We do this after disabling the counter to prevent
 * more threads from queueing up on the counter.
 *
 * Essentially, this means that we still need a lock in the fast path to enable
 * synchronisation between the global counters and the per-cpu counters. This
 * is not a problem because the lock will be local to a CPU almost all the time
 * and have little contention except when we get to ENOSPC conditions.
 *
 * Basically, this lock becomes a barrier that enables us to lock out the fast
 * path while we do things like enabling and disabling counters and
 * synchronising the counters.
 *
 * Locking rules:
 *
 *      1. m_sb_lock before picking up per-cpu locks
 *      2. per-cpu locks always picked up via for_each_online_cpu() order
 *      3. accurate counter sync requires m_sb_lock + per cpu locks
 *      4. modifying per-cpu counters requires holding per-cpu lock
 *      5. modifying global counters requires holding m_sb_lock
 *      6. enabling or disabling a counter requires holding the m_sb_lock 
 *         and _none_ of the per-cpu locks.
 *
 * Disabled counters are only ever re-enabled by a balance operation
 * that results in more free resources per CPU than a given threshold.
 * To ensure counters don't remain disabled, they are rebalanced when
 * the global resource goes above a higher threshold (i.e. some hysteresis
 * is present to prevent thrashing).
 */

#ifdef CONFIG_HOTPLUG_CPU
/*
 * hot-plug CPU notifier support.
 *
 * We need a notifier per filesystem as we need to be able to identify
 * the filesystem to balance the counters out. This is achieved by
 * having a notifier block embedded in the xfs_mount_t and doing pointer
 * magic to get the mount pointer from the notifier block address.
 */
STATIC int
xfs_icsb_cpu_notify(
        struct notifier_block *nfb,
        unsigned long action,
        void *hcpu)
{
        xfs_icsb_cnts_t *cntp;
        xfs_mount_t     *mp;

        mp = (xfs_mount_t *)container_of(nfb, xfs_mount_t, m_icsb_notifier);
        cntp = (xfs_icsb_cnts_t *)
                        per_cpu_ptr(mp->m_sb_cnts, (unsigned long)hcpu);
        switch (action) {
        case CPU_UP_PREPARE:
        case CPU_UP_PREPARE_FROZEN:
                /* Easy Case - initialize the area and locks, and
                 * then rebalance when online does everything else for us. */
                memset(cntp, 0, sizeof(xfs_icsb_cnts_t));
                break;
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
                xfs_icsb_lock(mp);
                xfs_icsb_balance_counter(mp, XFS_SBS_ICOUNT, 0);
                xfs_icsb_balance_counter(mp, XFS_SBS_IFREE, 0);
                xfs_icsb_balance_counter(mp, XFS_SBS_FDBLOCKS, 0);
                xfs_icsb_unlock(mp);
                break;
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                /* Disable all the counters, then fold the dead cpu's
                 * count into the total on the global superblock and
                 * re-enable the counters. */
                xfs_icsb_lock(mp);
                spin_lock(&mp->m_sb_lock);
                xfs_icsb_disable_counter(mp, XFS_SBS_ICOUNT);
                xfs_icsb_disable_counter(mp, XFS_SBS_IFREE);
                xfs_icsb_disable_counter(mp, XFS_SBS_FDBLOCKS);

                mp->m_sb.sb_icount += cntp->icsb_icount;
                mp->m_sb.sb_ifree += cntp->icsb_ifree;
                mp->m_sb.sb_fdblocks += cntp->icsb_fdblocks;

                memset(cntp, 0, sizeof(xfs_icsb_cnts_t));

                xfs_icsb_balance_counter_locked(mp, XFS_SBS_ICOUNT, 0);
                xfs_icsb_balance_counter_locked(mp, XFS_SBS_IFREE, 0);
                xfs_icsb_balance_counter_locked(mp, XFS_SBS_FDBLOCKS, 0);
                spin_unlock(&mp->m_sb_lock);
                xfs_icsb_unlock(mp);
                break;
        }

        return NOTIFY_OK;
}
#endif /* CONFIG_HOTPLUG_CPU */

int
xfs_icsb_init_counters(
        xfs_mount_t     *mp)
{
        xfs_icsb_cnts_t *cntp;
        int             i;

        mp->m_sb_cnts = alloc_percpu(xfs_icsb_cnts_t);
        if (mp->m_sb_cnts == NULL)
                return -ENOMEM;

        for_each_online_cpu(i) {
                cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
                memset(cntp, 0, sizeof(xfs_icsb_cnts_t));
        }

        mutex_init(&mp->m_icsb_mutex);

        /*
         * start with all counters disabled so that the
         * initial balance kicks us off correctly
         */
        mp->m_icsb_counters = -1;

#ifdef CONFIG_HOTPLUG_CPU
        mp->m_icsb_notifier.notifier_call = xfs_icsb_cpu_notify;
        mp->m_icsb_notifier.priority = 0;
        register_hotcpu_notifier(&mp->m_icsb_notifier);
#endif /* CONFIG_HOTPLUG_CPU */

        return 0;
}

void
xfs_icsb_reinit_counters(
        xfs_mount_t     *mp)
{
        xfs_icsb_lock(mp);
        /*
         * start with all counters disabled so that the
         * initial balance kicks us off correctly
         */
        mp->m_icsb_counters = -1;
        xfs_icsb_balance_counter(mp, XFS_SBS_ICOUNT, 0);
        xfs_icsb_balance_counter(mp, XFS_SBS_IFREE, 0);
        xfs_icsb_balance_counter(mp, XFS_SBS_FDBLOCKS, 0);
        xfs_icsb_unlock(mp);
}

void
xfs_icsb_destroy_counters(
        xfs_mount_t     *mp)
{
        if (mp->m_sb_cnts) {
                unregister_hotcpu_notifier(&mp->m_icsb_notifier);
                free_percpu(mp->m_sb_cnts);
        }
        mutex_destroy(&mp->m_icsb_mutex);
}

STATIC void
xfs_icsb_lock_cntr(
        xfs_icsb_cnts_t *icsbp)
{
        while (test_and_set_bit(XFS_ICSB_FLAG_LOCK, &icsbp->icsb_flags)) {
                ndelay(1000);
        }
}

STATIC void
xfs_icsb_unlock_cntr(
        xfs_icsb_cnts_t *icsbp)
{
        clear_bit(XFS_ICSB_FLAG_LOCK, &icsbp->icsb_flags);
}


STATIC void
xfs_icsb_lock_all_counters(
        xfs_mount_t     *mp)
{
        xfs_icsb_cnts_t *cntp;
        int             i;

        for_each_online_cpu(i) {
                cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
                xfs_icsb_lock_cntr(cntp);
        }
}

STATIC void
xfs_icsb_unlock_all_counters(
        xfs_mount_t     *mp)
{
        xfs_icsb_cnts_t *cntp;
        int             i;

        for_each_online_cpu(i) {
                cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
                xfs_icsb_unlock_cntr(cntp);
        }
}

STATIC void
xfs_icsb_count(
        xfs_mount_t     *mp,
        xfs_icsb_cnts_t *cnt,
        int             flags)
{
        xfs_icsb_cnts_t *cntp;
        int             i;

        memset(cnt, 0, sizeof(xfs_icsb_cnts_t));

        if (!(flags & XFS_ICSB_LAZY_COUNT))
                xfs_icsb_lock_all_counters(mp);

        for_each_online_cpu(i) {
                cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
                cnt->icsb_icount += cntp->icsb_icount;
                cnt->icsb_ifree += cntp->icsb_ifree;
                cnt->icsb_fdblocks += cntp->icsb_fdblocks;
        }

        if (!(flags & XFS_ICSB_LAZY_COUNT))
                xfs_icsb_unlock_all_counters(mp);
}

STATIC int
xfs_icsb_counter_disabled(
        xfs_mount_t     *mp,
        xfs_sb_field_t  field)
{
        ASSERT((field >= XFS_SBS_ICOUNT) && (field <= XFS_SBS_FDBLOCKS));
        return test_bit(field, &mp->m_icsb_counters);
}

STATIC void
xfs_icsb_disable_counter(
        xfs_mount_t     *mp,
        xfs_sb_field_t  field)
{
        xfs_icsb_cnts_t cnt;

        ASSERT((field >= XFS_SBS_ICOUNT) && (field <= XFS_SBS_FDBLOCKS));

        /*
         * If we are already disabled, then there is nothing to do
         * here. We check before locking all the counters to avoid
         * the expensive lock operation when being called in the
         * slow path and the counter is already disabled. This is
         * safe because the only time we set or clear this state is under
         * the m_icsb_mutex.
         */
        if (xfs_icsb_counter_disabled(mp, field))
                return;

        xfs_icsb_lock_all_counters(mp);
        if (!test_and_set_bit(field, &mp->m_icsb_counters)) {
                /* drain back to superblock */

                xfs_icsb_count(mp, &cnt, XFS_ICSB_LAZY_COUNT);
                switch(field) {
                case XFS_SBS_ICOUNT:
                        mp->m_sb.sb_icount = cnt.icsb_icount;
                        break;
                case XFS_SBS_IFREE:
                        mp->m_sb.sb_ifree = cnt.icsb_ifree;
                        break;
                case XFS_SBS_FDBLOCKS:
                        mp->m_sb.sb_fdblocks = cnt.icsb_fdblocks;
                        break;
                default:
                        BUG();
                }
        }

        xfs_icsb_unlock_all_counters(mp);
}

STATIC void
xfs_icsb_enable_counter(
        xfs_mount_t     *mp,
        xfs_sb_field_t  field,
        uint64_t        count,
        uint64_t        resid)
{
        xfs_icsb_cnts_t *cntp;
        int             i;

        ASSERT((field >= XFS_SBS_ICOUNT) && (field <= XFS_SBS_FDBLOCKS));

        xfs_icsb_lock_all_counters(mp);
        for_each_online_cpu(i) {
                cntp = per_cpu_ptr(mp->m_sb_cnts, i);
                switch (field) {
                case XFS_SBS_ICOUNT:
                        cntp->icsb_icount = count + resid;
                        break;
                case XFS_SBS_IFREE:
                        cntp->icsb_ifree = count + resid;
                        break;
                case XFS_SBS_FDBLOCKS:
                        cntp->icsb_fdblocks = count + resid;
                        break;
                default:
                        BUG();
                        break;
                }
                resid = 0;
        }
        clear_bit(field, &mp->m_icsb_counters);
        xfs_icsb_unlock_all_counters(mp);
}

void
xfs_icsb_sync_counters_locked(
        xfs_mount_t     *mp,
        int             flags)
{
        xfs_icsb_cnts_t cnt;

        xfs_icsb_count(mp, &cnt, flags);

        if (!xfs_icsb_counter_disabled(mp, XFS_SBS_ICOUNT))
                mp->m_sb.sb_icount = cnt.icsb_icount;
        if (!xfs_icsb_counter_disabled(mp, XFS_SBS_IFREE))
                mp->m_sb.sb_ifree = cnt.icsb_ifree;
        if (!xfs_icsb_counter_disabled(mp, XFS_SBS_FDBLOCKS))
                mp->m_sb.sb_fdblocks = cnt.icsb_fdblocks;
}

/*
 * Accurate update of per-cpu counters to incore superblock
 */
void
xfs_icsb_sync_counters(
        xfs_mount_t     *mp,
        int             flags)
{
        spin_lock(&mp->m_sb_lock);
        xfs_icsb_sync_counters_locked(mp, flags);
        spin_unlock(&mp->m_sb_lock);
}

/*
 * Balance and enable/disable counters as necessary.
 *
 * Thresholds for re-enabling counters are somewhat magic.  inode counts are
 * chosen to be the same number as single on disk allocation chunk per CPU, and
 * free blocks is something far enough zero that we aren't going thrash when we
 * get near ENOSPC. We also need to supply a minimum we require per cpu to
 * prevent looping endlessly when xfs_alloc_space asks for more than will
 * be distributed to a single CPU but each CPU has enough blocks to be
 * reenabled.
 *
 * Note that we can be called when counters are already disabled.
 * xfs_icsb_disable_counter() optimises the counter locking in this case to
 * prevent locking every per-cpu counter needlessly.
 */

#define XFS_ICSB_INO_CNTR_REENABLE      (uint64_t)64
#define XFS_ICSB_FDBLK_CNTR_REENABLE(mp) \
                (uint64_t)(512 + XFS_ALLOC_SET_ASIDE(mp))
STATIC void
xfs_icsb_balance_counter_locked(
        xfs_mount_t     *mp,
        xfs_sb_field_t  field,
        int             min_per_cpu)
{
        uint64_t        count, resid;
        int             weight = num_online_cpus();
        uint64_t        min = (uint64_t)min_per_cpu;

        /* disable counter and sync counter */
        xfs_icsb_disable_counter(mp, field);

        /* update counters  - first CPU gets residual*/
        switch (field) {
        case XFS_SBS_ICOUNT:
                count = mp->m_sb.sb_icount;
                resid = do_div(count, weight);
                if (count < max(min, XFS_ICSB_INO_CNTR_REENABLE))
                        return;
                break;
        case XFS_SBS_IFREE:
                count = mp->m_sb.sb_ifree;
                resid = do_div(count, weight);
                if (count < max(min, XFS_ICSB_INO_CNTR_REENABLE))
                        return;
                break;
        case XFS_SBS_FDBLOCKS:
                count = mp->m_sb.sb_fdblocks;
                resid = do_div(count, weight);
                if (count < max(min, XFS_ICSB_FDBLK_CNTR_REENABLE(mp)))
                        return;
                break;
        default:
                BUG();
                count = resid = 0;      /* quiet, gcc */
                break;
        }

        xfs_icsb_enable_counter(mp, field, count, resid);
}

STATIC void
xfs_icsb_balance_counter(
        xfs_mount_t     *mp,
        xfs_sb_field_t  fields,
        int             min_per_cpu)
{
        spin_lock(&mp->m_sb_lock);
        xfs_icsb_balance_counter_locked(mp, fields, min_per_cpu);
        spin_unlock(&mp->m_sb_lock);
}

int
xfs_icsb_modify_counters(
        xfs_mount_t     *mp,
        xfs_sb_field_t  field,
        int64_t         delta,
        int             rsvd)
{
        xfs_icsb_cnts_t *icsbp;
        long long       lcounter;       /* long counter for 64 bit fields */
        int             ret = 0;

        might_sleep();
again:
        preempt_disable();
        icsbp = this_cpu_ptr(mp->m_sb_cnts);

        /*
         * if the counter is disabled, go to slow path
         */
        if (unlikely(xfs_icsb_counter_disabled(mp, field)))
                goto slow_path;
        xfs_icsb_lock_cntr(icsbp);
        if (unlikely(xfs_icsb_counter_disabled(mp, field))) {
                xfs_icsb_unlock_cntr(icsbp);
                goto slow_path;
        }

        switch (field) {
        case XFS_SBS_ICOUNT:
                lcounter = icsbp->icsb_icount;
                lcounter += delta;
                if (unlikely(lcounter < 0))
                        goto balance_counter;
                icsbp->icsb_icount = lcounter;
                break;

        case XFS_SBS_IFREE:
                lcounter = icsbp->icsb_ifree;
                lcounter += delta;
                if (unlikely(lcounter < 0))
                        goto balance_counter;
                icsbp->icsb_ifree = lcounter;
                break;

        case XFS_SBS_FDBLOCKS:
                BUG_ON((mp->m_resblks - mp->m_resblks_avail) != 0);

                lcounter = icsbp->icsb_fdblocks - XFS_ALLOC_SET_ASIDE(mp);
                lcounter += delta;
                if (unlikely(lcounter < 0))
                        goto balance_counter;
                icsbp->icsb_fdblocks = lcounter + XFS_ALLOC_SET_ASIDE(mp);
                break;
        default:
                BUG();
                break;
        }
        xfs_icsb_unlock_cntr(icsbp);
        preempt_enable();
        return 0;

slow_path:
        preempt_enable();

        /*
         * serialise with a mutex so we don't burn lots of cpu on
         * the superblock lock. We still need to hold the superblock
         * lock, however, when we modify the global structures.
         */
        xfs_icsb_lock(mp);

        /*
         * Now running atomically.
         *
         * If the counter is enabled, someone has beaten us to rebalancing.
         * Drop the lock and try again in the fast path....
         */
        if (!(xfs_icsb_counter_disabled(mp, field))) {
                xfs_icsb_unlock(mp);
                goto again;
        }

        /*
         * The counter is currently disabled. Because we are
         * running atomically here, we know a rebalance cannot
         * be in progress. Hence we can go straight to operating
         * on the global superblock. We do not call xfs_mod_incore_sb()
         * here even though we need to get the m_sb_lock. Doing so
         * will cause us to re-enter this function and deadlock.
         * Hence we get the m_sb_lock ourselves and then call
         * xfs_mod_incore_sb_unlocked() as the unlocked path operates
         * directly on the global counters.
         */
        spin_lock(&mp->m_sb_lock);
        ret = xfs_mod_incore_sb_unlocked(mp, field, delta, rsvd);
        spin_unlock(&mp->m_sb_lock);

        /*
         * Now that we've modified the global superblock, we
         * may be able to re-enable the distributed counters
         * (e.g. lots of space just got freed). After that
         * we are done.
         */
        if (ret != ENOSPC)
                xfs_icsb_balance_counter(mp, field, 0);
        xfs_icsb_unlock(mp);
        return ret;

balance_counter:
        xfs_icsb_unlock_cntr(icsbp);
        preempt_enable();

        /*
         * We may have multiple threads here if multiple per-cpu
         * counters run dry at the same time. This will mean we can
         * do more balances than strictly necessary but it is not
         * the common slowpath case.
         */
        xfs_icsb_lock(mp);

        /*
         * running atomically.
         *
         * This will leave the counter in the correct state for future
         * accesses. After the rebalance, we simply try again and our retry
         * will either succeed through the fast path or slow path without
         * another balance operation being required.
         */
        xfs_icsb_balance_counter(mp, field, delta);
        xfs_icsb_unlock(mp);
        goto again;
}

#endif