xfs: Add trace points for per-ag refcount debugging.

[linux-2.6-block.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_types.h"
#include "xfs_bit.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_dir2.h"
#include "xfs_dmapi.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_dir2_sf.h"
#include "xfs_attr_sf.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_btree.h"
#include "xfs_ialloc.h"
#include "xfs_alloc.h"
#include "xfs_rtalloc.h"
#include "xfs_bmap.h"
#include "xfs_error.h"
#include "xfs_rw.h"
#include "xfs_quota.h"
#include "xfs_fsops.h"
#include "xfs_utils.h"
#include "xfs_trace.h"


STATIC void     xfs_unmountfs_wait(xfs_mount_t *);


#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 int      xfs_icsb_modify_counters(xfs_mount_t *, xfs_sb_field_t,
                                                int64_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)
#define xfs_icsb_modify_counters(mp, a, b, c)           do { } while (0)

#endif

static const struct {
        short offset;
        short type;     /* 0 = integer
                         * 1 = binary / string (no translation)
                         */
} xfs_sb_info[] = {
    { offsetof(xfs_sb_t, sb_magicnum),   0 },
    { offsetof(xfs_sb_t, sb_blocksize),  0 },
    { offsetof(xfs_sb_t, sb_dblocks),    0 },
    { offsetof(xfs_sb_t, sb_rblocks),    0 },
    { offsetof(xfs_sb_t, sb_rextents),   0 },
    { offsetof(xfs_sb_t, sb_uuid),       1 },
    { offsetof(xfs_sb_t, sb_logstart),   0 },
    { offsetof(xfs_sb_t, sb_rootino),    0 },
    { offsetof(xfs_sb_t, sb_rbmino),     0 },
    { offsetof(xfs_sb_t, sb_rsumino),    0 },
    { offsetof(xfs_sb_t, sb_rextsize),   0 },
    { offsetof(xfs_sb_t, sb_agblocks),   0 },
    { offsetof(xfs_sb_t, sb_agcount),    0 },
    { offsetof(xfs_sb_t, sb_rbmblocks),  0 },
    { offsetof(xfs_sb_t, sb_logblocks),  0 },
    { offsetof(xfs_sb_t, sb_versionnum), 0 },
    { offsetof(xfs_sb_t, sb_sectsize),   0 },
    { offsetof(xfs_sb_t, sb_inodesize),  0 },
    { offsetof(xfs_sb_t, sb_inopblock),  0 },
    { offsetof(xfs_sb_t, sb_fname[0]),   1 },
    { offsetof(xfs_sb_t, sb_blocklog),   0 },
    { offsetof(xfs_sb_t, sb_sectlog),    0 },
    { offsetof(xfs_sb_t, sb_inodelog),   0 },
    { offsetof(xfs_sb_t, sb_inopblog),   0 },
    { offsetof(xfs_sb_t, sb_agblklog),   0 },
    { offsetof(xfs_sb_t, sb_rextslog),   0 },
    { offsetof(xfs_sb_t, sb_inprogress), 0 },
    { offsetof(xfs_sb_t, sb_imax_pct),   0 },
    { offsetof(xfs_sb_t, sb_icount),     0 },
    { offsetof(xfs_sb_t, sb_ifree),      0 },
    { offsetof(xfs_sb_t, sb_fdblocks),   0 },
    { offsetof(xfs_sb_t, sb_frextents),  0 },
    { offsetof(xfs_sb_t, sb_uquotino),   0 },
    { offsetof(xfs_sb_t, sb_gquotino),   0 },
    { offsetof(xfs_sb_t, sb_qflags),     0 },
    { offsetof(xfs_sb_t, sb_flags),      0 },
    { offsetof(xfs_sb_t, sb_shared_vn),  0 },
    { offsetof(xfs_sb_t, sb_inoalignmt), 0 },
    { offsetof(xfs_sb_t, sb_unit),       0 },
    { offsetof(xfs_sb_t, sb_width),      0 },
    { offsetof(xfs_sb_t, sb_dirblklog),  0 },
    { offsetof(xfs_sb_t, sb_logsectlog), 0 },
    { offsetof(xfs_sb_t, sb_logsectsize),0 },
    { offsetof(xfs_sb_t, sb_logsunit),   0 },
    { offsetof(xfs_sb_t, sb_features2),  0 },
    { offsetof(xfs_sb_t, sb_bad_features2), 0 },
    { sizeof(xfs_sb_t),                  0 }
};

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)) {
                cmn_err(CE_WARN,
                        "XFS: Filesystem %s has nil UUID - can't mount",
                        mp->m_fsname);
                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);
        cmn_err(CE_WARN, "XFS: Filesystem %s has duplicate UUID - can't mount",
                         mp->m_fsname);
        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);
}


/*
 * Reference counting access wrappers to the perag structures.
 */
struct xfs_perag *
xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
{
        struct xfs_perag        *pag;
        int                     ref = 0;

        spin_lock(&mp->m_perag_lock);
        pag = radix_tree_lookup(&mp->m_perag_tree, agno);
        if (pag) {
                ASSERT(atomic_read(&pag->pag_ref) >= 0);
                /* catch leaks in the positive direction during testing */
                ASSERT(atomic_read(&pag->pag_ref) < 1000);
                ref = atomic_inc_return(&pag->pag_ref);
        }
        spin_unlock(&mp->m_perag_lock);
        trace_xfs_perag_get(mp, agno, ref, _RET_IP_);
        return pag;
}

void
xfs_perag_put(struct xfs_perag *pag)
{
        int     ref;

        ASSERT(atomic_read(&pag->pag_ref) > 0);
        ref = atomic_dec_return(&pag->pag_ref);
        trace_xfs_perag_put(pag->pag_mount, pag->pag_agno, ref, _RET_IP_);
}

/*
 * Free up the resources associated with a mount structure.  Assume that
 * the structure was initially zeroed, so we can tell which fields got
 * initialized.
 */
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);
                ASSERT(atomic_read(&pag->pag_ref) == 0);
                spin_unlock(&mp->m_perag_lock);
                ASSERT(pag);
                kmem_free(pag->pagb_list);
                kmem_free(pag);
        }
}

/*
 * 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 E2BIG;
#else                  /* Limited by UINT_MAX of sectors */
        if (nblocks << (sbp->sb_blocklog - BBSHIFT) > UINT_MAX)
                return E2BIG;
#endif
        return 0;
}

/*
 * Check the validity of the SB found.
 */
STATIC int
xfs_mount_validate_sb(
        xfs_mount_t     *mp,
        xfs_sb_t        *sbp,
        int             flags)
{
        /*
         * If the log device and data device have the
         * same device number, the log is internal.
         * Consequently, the sb_logstart should be non-zero.  If
         * we have a zero sb_logstart in this case, we may be trying to mount
         * a volume filesystem in a non-volume manner.
         */
        if (sbp->sb_magicnum != XFS_SB_MAGIC) {
                xfs_fs_mount_cmn_err(flags, "bad magic number");
                return XFS_ERROR(EWRONGFS);
        }

        if (!xfs_sb_good_version(sbp)) {
                xfs_fs_mount_cmn_err(flags, "bad version");
                return XFS_ERROR(EWRONGFS);
        }

        if (unlikely(
            sbp->sb_logstart == 0 && mp->m_logdev_targp == mp->m_ddev_targp)) {
                xfs_fs_mount_cmn_err(flags,
                        "filesystem is marked as having an external log; "
                        "specify logdev on the\nmount command line.");
                return XFS_ERROR(EINVAL);
        }

        if (unlikely(
            sbp->sb_logstart != 0 && mp->m_logdev_targp != mp->m_ddev_targp)) {
                xfs_fs_mount_cmn_err(flags,
                        "filesystem is marked as having an internal log; "
                        "do not specify logdev on\nthe mount command line.");
                return XFS_ERROR(EINVAL);
        }

        /*
         * More sanity checking. These were stolen directly from
         * xfs_repair.
         */
        if (unlikely(
            sbp->sb_agcount <= 0                                        ||
            sbp->sb_sectsize < XFS_MIN_SECTORSIZE                       ||
            sbp->sb_sectsize > XFS_MAX_SECTORSIZE                       ||
            sbp->sb_sectlog < XFS_MIN_SECTORSIZE_LOG                    ||
            sbp->sb_sectlog > XFS_MAX_SECTORSIZE_LOG                    ||
            sbp->sb_sectsize != (1 << sbp->sb_sectlog)                  ||
            sbp->sb_blocksize < XFS_MIN_BLOCKSIZE                       ||
            sbp->sb_blocksize > XFS_MAX_BLOCKSIZE                       ||
            sbp->sb_blocklog < XFS_MIN_BLOCKSIZE_LOG                    ||
            sbp->sb_blocklog > XFS_MAX_BLOCKSIZE_LOG                    ||
            sbp->sb_blocksize != (1 << sbp->sb_blocklog)                ||
            sbp->sb_inodesize < XFS_DINODE_MIN_SIZE                     ||
            sbp->sb_inodesize > XFS_DINODE_MAX_SIZE                     ||
            sbp->sb_inodelog < XFS_DINODE_MIN_LOG                       ||
            sbp->sb_inodelog > XFS_DINODE_MAX_LOG                       ||
            sbp->sb_inodesize != (1 << sbp->sb_inodelog)                ||
            (sbp->sb_blocklog - sbp->sb_inodelog != sbp->sb_inopblog)   ||
            (sbp->sb_rextsize * sbp->sb_blocksize > XFS_MAX_RTEXTSIZE)  ||
            (sbp->sb_rextsize * sbp->sb_blocksize < XFS_MIN_RTEXTSIZE)  ||
            (sbp->sb_imax_pct > 100 /* zero sb_imax_pct is valid */))) {
                xfs_fs_mount_cmn_err(flags, "SB sanity check 1 failed");
                return XFS_ERROR(EFSCORRUPTED);
        }

        /*
         * Sanity check AG count, size fields against data size field
         */
        if (unlikely(
            sbp->sb_dblocks == 0 ||
            sbp->sb_dblocks >
             (xfs_drfsbno_t)sbp->sb_agcount * sbp->sb_agblocks ||
            sbp->sb_dblocks < (xfs_drfsbno_t)(sbp->sb_agcount - 1) *
                              sbp->sb_agblocks + XFS_MIN_AG_BLOCKS)) {
                xfs_fs_mount_cmn_err(flags, "SB sanity check 2 failed");
                return XFS_ERROR(EFSCORRUPTED);
        }

        /*
         * Until this is fixed only page-sized or smaller data blocks work.
         */
        if (unlikely(sbp->sb_blocksize > PAGE_SIZE)) {
                xfs_fs_mount_cmn_err(flags,
                        "file system with blocksize %d bytes",
                        sbp->sb_blocksize);
                xfs_fs_mount_cmn_err(flags,
                        "only pagesize (%ld) or less will currently work.",
                        PAGE_SIZE);
                return XFS_ERROR(ENOSYS);
        }

        /*
         * Currently only very few inode sizes are supported.
         */
        switch (sbp->sb_inodesize) {
        case 256:
        case 512:
        case 1024:
        case 2048:
                break;
        default:
                xfs_fs_mount_cmn_err(flags,
                        "inode size of %d bytes not supported",
                        sbp->sb_inodesize);
                return XFS_ERROR(ENOSYS);
        }

        if (xfs_sb_validate_fsb_count(sbp, sbp->sb_dblocks) ||
            xfs_sb_validate_fsb_count(sbp, sbp->sb_rblocks)) {
                xfs_fs_mount_cmn_err(flags,
                        "file system too large to be mounted on this system.");
                return XFS_ERROR(E2BIG);
        }

        if (unlikely(sbp->sb_inprogress)) {
                xfs_fs_mount_cmn_err(flags, "file system busy");
                return XFS_ERROR(EFSCORRUPTED);
        }

        /*
         * Version 1 directory format has never worked on Linux.
         */
        if (unlikely(!xfs_sb_version_hasdirv2(sbp))) {
                xfs_fs_mount_cmn_err(flags,
                        "file system using version 1 directory format");
                return XFS_ERROR(ENOSYS);
        }

        return 0;
}

STATIC void
xfs_initialize_perag_icache(
        xfs_perag_t     *pag)
{
        if (!pag->pag_ici_init) {
                rwlock_init(&pag->pag_ici_lock);
                INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC);
                pag->pag_ici_init = 1;
        }
}

int
xfs_initialize_perag(
        xfs_mount_t     *mp,
        xfs_agnumber_t  agcount,
        xfs_agnumber_t  *maxagi)
{
        xfs_agnumber_t  index, max_metadata;
        xfs_perag_t     *pag;
        xfs_agino_t     agino;
        xfs_ino_t       ino;
        xfs_sb_t        *sbp = &mp->m_sb;
        xfs_ino_t       max_inum = XFS_MAXINUMBER_32;

        /* Check to see if the filesystem can overflow 32 bit inodes */
        agino = XFS_OFFBNO_TO_AGINO(mp, sbp->sb_agblocks - 1, 0);
        ino = XFS_AGINO_TO_INO(mp, agcount - 1, agino);

        /*
         * 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;
                }
                pag = kmem_zalloc(sizeof(*pag), KM_MAYFAIL);
                if (!pag)
                        return -ENOMEM;
                if (radix_tree_preload(GFP_NOFS))
                        return -ENOMEM;
                spin_lock(&mp->m_perag_lock);
                if (radix_tree_insert(&mp->m_perag_tree, index, pag)) {
                        BUG();
                        spin_unlock(&mp->m_perag_lock);
                        kmem_free(pag);
                        return -EEXIST;
                }
                pag->pag_agno = index;
                pag->pag_mount = mp;
                spin_unlock(&mp->m_perag_lock);
                radix_tree_preload_end();
        }

        /* Clear the mount flag if no inode can overflow 32 bits
         * on this filesystem, or if specifically requested..
         */
        if ((mp->m_flags & XFS_MOUNT_SMALL_INUMS) && ino > max_inum) {
                mp->m_flags |= XFS_MOUNT_32BITINODES;
        } else {
                mp->m_flags &= ~XFS_MOUNT_32BITINODES;
        }

        /* If we can overflow then setup the ag headers accordingly */
        if (mp->m_flags & XFS_MOUNT_32BITINODES) {
                /* Calculate how much should be reserved for inodes to
                 * meet the max inode percentage.
                 */
                if (mp->m_maxicount) {
                        __uint64_t      icount;

                        icount = sbp->sb_dblocks * sbp->sb_imax_pct;
                        do_div(icount, 100);
                        icount += sbp->sb_agblocks - 1;
                        do_div(icount, sbp->sb_agblocks);
                        max_metadata = icount;
                } else {
                        max_metadata = agcount;
                }
                for (index = 0; index < agcount; index++) {
                        ino = XFS_AGINO_TO_INO(mp, index, agino);
                        if (ino > max_inum) {
                                index++;
                                break;
                        }

                        /* This ag is preferred for inodes */
                        pag = xfs_perag_get(mp, index);
                        pag->pagi_inodeok = 1;
                        if (index < max_metadata)
                                pag->pagf_metadata = 1;
                        xfs_initialize_perag_icache(pag);
                        xfs_perag_put(pag);
                }
        } else {
                /* Setup default behavior for smaller filesystems */
                for (index = 0; index < agcount; index++) {
                        pag = xfs_perag_get(mp, index);
                        pag->pagi_inodeok = 1;
                        xfs_initialize_perag_icache(pag);
                        xfs_perag_put(pag);
                }
        }
        if (maxagi)
                *maxagi = index;
        return 0;
}

void
xfs_sb_from_disk(
        xfs_sb_t        *to,
        xfs_dsb_t       *from)
{
        to->sb_magicnum = be32_to_cpu(from->sb_magicnum);
        to->sb_blocksize = be32_to_cpu(from->sb_blocksize);
        to->sb_dblocks = be64_to_cpu(from->sb_dblocks);
        to->sb_rblocks = be64_to_cpu(from->sb_rblocks);
        to->sb_rextents = be64_to_cpu(from->sb_rextents);
        memcpy(&to->sb_uuid, &from->sb_uuid, sizeof(to->sb_uuid));
        to->sb_logstart = be64_to_cpu(from->sb_logstart);
        to->sb_rootino = be64_to_cpu(from->sb_rootino);
        to->sb_rbmino = be64_to_cpu(from->sb_rbmino);
        to->sb_rsumino = be64_to_cpu(from->sb_rsumino);
        to->sb_rextsize = be32_to_cpu(from->sb_rextsize);
        to->sb_agblocks = be32_to_cpu(from->sb_agblocks);
        to->sb_agcount = be32_to_cpu(from->sb_agcount);
        to->sb_rbmblocks = be32_to_cpu(from->sb_rbmblocks);
        to->sb_logblocks = be32_to_cpu(from->sb_logblocks);
        to->sb_versionnum = be16_to_cpu(from->sb_versionnum);
        to->sb_sectsize = be16_to_cpu(from->sb_sectsize);
        to->sb_inodesize = be16_to_cpu(from->sb_inodesize);
        to->sb_inopblock = be16_to_cpu(from->sb_inopblock);
        memcpy(&to->sb_fname, &from->sb_fname, sizeof(to->sb_fname));
        to->sb_blocklog = from->sb_blocklog;
        to->sb_sectlog = from->sb_sectlog;
        to->sb_inodelog = from->sb_inodelog;
        to->sb_inopblog = from->sb_inopblog;
        to->sb_agblklog = from->sb_agblklog;
        to->sb_rextslog = from->sb_rextslog;
        to->sb_inprogress = from->sb_inprogress;
        to->sb_imax_pct = from->sb_imax_pct;
        to->sb_icount = be64_to_cpu(from->sb_icount);
        to->sb_ifree = be64_to_cpu(from->sb_ifree);
        to->sb_fdblocks = be64_to_cpu(from->sb_fdblocks);
        to->sb_frextents = be64_to_cpu(from->sb_frextents);
        to->sb_uquotino = be64_to_cpu(from->sb_uquotino);
        to->sb_gquotino = be64_to_cpu(from->sb_gquotino);
        to->sb_qflags = be16_to_cpu(from->sb_qflags);
        to->sb_flags = from->sb_flags;
        to->sb_shared_vn = from->sb_shared_vn;
        to->sb_inoalignmt = be32_to_cpu(from->sb_inoalignmt);
        to->sb_unit = be32_to_cpu(from->sb_unit);
        to->sb_width = be32_to_cpu(from->sb_width);
        to->sb_dirblklog = from->sb_dirblklog;
        to->sb_logsectlog = from->sb_logsectlog;
        to->sb_logsectsize = be16_to_cpu(from->sb_logsectsize);
        to->sb_logsunit = be32_to_cpu(from->sb_logsunit);
        to->sb_features2 = be32_to_cpu(from->sb_features2);
        to->sb_bad_features2 = be32_to_cpu(from->sb_bad_features2);
}

/*
 * Copy in core superblock to ondisk one.
 *
 * The fields argument is mask of superblock fields to copy.
 */
void
xfs_sb_to_disk(
        xfs_dsb_t       *to,
        xfs_sb_t        *from,
        __int64_t       fields)
{
        xfs_caddr_t     to_ptr = (xfs_caddr_t)to;
        xfs_caddr_t     from_ptr = (xfs_caddr_t)from;
        xfs_sb_field_t  f;
        int             first;
        int             size;

        ASSERT(fields);
        if (!fields)
                return;

        while (fields) {
                f = (xfs_sb_field_t)xfs_lowbit64((__uint64_t)fields);
                first = xfs_sb_info[f].offset;
                size = xfs_sb_info[f + 1].offset - first;

                ASSERT(xfs_sb_info[f].type == 0 || xfs_sb_info[f].type == 1);

                if (size == 1 || xfs_sb_info[f].type == 1) {
                        memcpy(to_ptr + first, from_ptr + first, size);
                } else {
                        switch (size) {
                        case 2:
                                *(__be16 *)(to_ptr + first) =
                                        cpu_to_be16(*(__u16 *)(from_ptr + first));
                                break;
                        case 4:
                                *(__be32 *)(to_ptr + first) =
                                        cpu_to_be32(*(__u32 *)(from_ptr + first));
                                break;
                        case 8:
                                *(__be64 *)(to_ptr + first) =
                                        cpu_to_be64(*(__u64 *)(from_ptr + first));
                                break;
                        default:
                                ASSERT(0);
                        }
                }

                fields &= ~(1LL << f);
        }
}

/*
 * xfs_readsb
 *
 * Does the initial read of the superblock.
 */
int
xfs_readsb(xfs_mount_t *mp, int flags)
{
        unsigned int    sector_size;
        unsigned int    extra_flags;
        xfs_buf_t       *bp;
        int             error;

        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);
        extra_flags = XFS_BUF_LOCK | XFS_BUF_MANAGE | XFS_BUF_MAPPED;

        bp = xfs_buf_read(mp->m_ddev_targp, XFS_SB_DADDR, BTOBB(sector_size),
                          extra_flags);
        if (!bp || XFS_BUF_ISERROR(bp)) {
                xfs_fs_mount_cmn_err(flags, "SB read failed");
                error = bp ? XFS_BUF_GETERROR(bp) : ENOMEM;
                goto fail;
        }
        ASSERT(XFS_BUF_ISBUSY(bp));
        ASSERT(XFS_BUF_VALUSEMA(bp) <= 0);

        /*
         * Initialize the mount structure from the superblock.
         * But first do some basic consistency checking.
         */
        xfs_sb_from_disk(&mp->m_sb, XFS_BUF_TO_SBP(bp));

        error = xfs_mount_validate_sb(mp, &(mp->m_sb), flags);
        if (error) {
                xfs_fs_mount_cmn_err(flags, "SB validate failed");
                goto fail;
        }

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

        /*
         * If device sector size is smaller than the superblock size,
         * re-read the superblock so the buffer is correctly sized.
         */
        if (sector_size < mp->m_sb.sb_sectsize) {
                XFS_BUF_UNMANAGE(bp);
                xfs_buf_relse(bp);
                sector_size = mp->m_sb.sb_sectsize;
                bp = xfs_buf_read(mp->m_ddev_targp, XFS_SB_DADDR,
                                  BTOBB(sector_size), extra_flags);
                if (!bp || XFS_BUF_ISERROR(bp)) {
                        xfs_fs_mount_cmn_err(flags, "SB re-read failed");
                        error = bp ? XFS_BUF_GETERROR(bp) : ENOMEM;
                        goto fail;
                }
                ASSERT(XFS_BUF_ISBUSY(bp));
                ASSERT(XFS_BUF_VALUSEMA(bp) <= 0);
        }

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

        mp->m_sb_bp = bp;
        xfs_buf_relse(bp);
        ASSERT(XFS_BUF_VALUSEMA(bp) > 0);
        return 0;

 fail:
        if (bp) {
                XFS_BUF_UNMANAGE(bp);
                xfs_buf_relse(bp);
        }
        return error;
}


/*
 * xfs_mount_common
 *
 * Mount initialization code establishing various mount
 * fields from the superblock associated with the given
 * mount structure
 */
STATIC void
xfs_mount_common(xfs_mount_t *mp, xfs_sb_t *sbp)
{
        mp->m_agfrotor = mp->m_agirotor = 0;
        spin_lock_init(&mp->m_agirotor_lock);
        mp->m_maxagi = mp->m_sb.sb_agcount;
        mp->m_blkbit_log = sbp->sb_blocklog + XFS_NBBYLOG;
        mp->m_blkbb_log = sbp->sb_blocklog - BBSHIFT;
        mp->m_sectbb_log = sbp->sb_sectlog - BBSHIFT;
        mp->m_agno_log = xfs_highbit32(sbp->sb_agcount - 1) + 1;
        mp->m_agino_log = sbp->sb_inopblog + sbp->sb_agblklog;
        mp->m_blockmask = sbp->sb_blocksize - 1;
        mp->m_blockwsize = sbp->sb_blocksize >> XFS_WORDLOG;
        mp->m_blockwmask = mp->m_blockwsize - 1;

        mp->m_alloc_mxr[0] = xfs_allocbt_maxrecs(mp, sbp->sb_blocksize, 1);
        mp->m_alloc_mxr[1] = xfs_allocbt_maxrecs(mp, sbp->sb_blocksize, 0);
        mp->m_alloc_mnr[0] = mp->m_alloc_mxr[0] / 2;
        mp->m_alloc_mnr[1] = mp->m_alloc_mxr[1] / 2;

        mp->m_inobt_mxr[0] = xfs_inobt_maxrecs(mp, sbp->sb_blocksize, 1);
        mp->m_inobt_mxr[1] = xfs_inobt_maxrecs(mp, sbp->sb_blocksize, 0);
        mp->m_inobt_mnr[0] = mp->m_inobt_mxr[0] / 2;
        mp->m_inobt_mnr[1] = mp->m_inobt_mxr[1] / 2;

        mp->m_bmap_dmxr[0] = xfs_bmbt_maxrecs(mp, sbp->sb_blocksize, 1);
        mp->m_bmap_dmxr[1] = xfs_bmbt_maxrecs(mp, sbp->sb_blocksize, 0);
        mp->m_bmap_dmnr[0] = mp->m_bmap_dmxr[0] / 2;
        mp->m_bmap_dmnr[1] = mp->m_bmap_dmxr[1] / 2;

        mp->m_bsize = XFS_FSB_TO_BB(mp, 1);
        mp->m_ialloc_inos = (int)MAX((__uint16_t)XFS_INODES_PER_CHUNK,
                                        sbp->sb_inopblock);
        mp->m_ialloc_blks = mp->m_ialloc_inos >> sbp->sb_inopblog;
}

/*
 * xfs_initialize_perag_data
 *
 * Read in each per-ag structure so we can count up the number of
 * allocated inodes, free inodes and used filesystem blocks as this
 * information is no longer persistent in the superblock. Once we have
 * this information, write it into the in-core superblock structure.
 */
STATIC int
xfs_initialize_perag_data(xfs_mount_t *mp, xfs_agnumber_t agcount)
{
        xfs_agnumber_t  index;
        xfs_perag_t     *pag;
        xfs_sb_t        *sbp = &mp->m_sb;
        uint64_t        ifree = 0;
        uint64_t        ialloc = 0;
        uint64_t        bfree = 0;
        uint64_t        bfreelst = 0;
        uint64_t        btree = 0;
        int             error;

        for (index = 0; index < agcount; index++) {
                /*
                 * read the agf, then the agi. This gets us
                 * all the information we need and populates the
                 * per-ag structures for us.
                 */
                error = xfs_alloc_pagf_init(mp, NULL, index, 0);
                if (error)
                        return error;

                error = xfs_ialloc_pagi_init(mp, NULL, index);
                if (error)
                        return error;
                pag = xfs_perag_get(mp, index);
                ifree += pag->pagi_freecount;
                ialloc += pag->pagi_count;
                bfree += pag->pagf_freeblks;
                bfreelst += pag->pagf_flcount;
                btree += pag->pagf_btreeblks;
                xfs_perag_put(pag);
        }
        /*
         * Overwrite incore superblock counters with just-read data
         */
        spin_lock(&mp->m_sb_lock);
        sbp->sb_ifree = ifree;
        sbp->sb_icount = ialloc;
        sbp->sb_fdblocks = bfree + bfreelst + btree;
        spin_unlock(&mp->m_sb_lock);

        /* Fixup the per-cpu counters as well. */
        xfs_icsb_reinit_counters(mp);

        return 0;
}

/*
 * 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)) {
                        if (mp->m_flags & XFS_MOUNT_RETERR) {
                                cmn_err(CE_WARN,
                                        "XFS: alignment check 1 failed");
                                return XFS_ERROR(EINVAL);
                        }
                        mp->m_dalign = mp->m_swidth = 0;
                } 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)) {
                                if (mp->m_flags & XFS_MOUNT_RETERR) {
                                        return XFS_ERROR(EINVAL);
                                }
                                xfs_fs_cmn_err(CE_WARN, mp,
"stripe alignment turned off: sunit(%d)/swidth(%d) incompatible with agsize(%d)",
                                        mp->m_dalign, mp->m_swidth,
                                        sbp->sb_agblocks);

                                mp->m_dalign = 0;
                                mp->m_swidth = 0;
                        } else if (mp->m_dalign) {
                                mp->m_swidth = XFS_BB_TO_FSBT(mp, mp->m_swidth);
                        } else {
                                if (mp->m_flags & XFS_MOUNT_RETERR) {
                                        xfs_fs_cmn_err(CE_WARN, mp,
"stripe alignment turned off: sunit(%d) less than bsize(%d)",
                                                mp->m_dalign,
                                                mp->m_blockmask +1);
                                        return XFS_ERROR(EINVAL);
                                }
                                mp->m_swidth = 0;
                        }
                }

                /*
                 * 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 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);
}

/*
 * 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) are an ok size.
 */
STATIC int
xfs_check_sizes(xfs_mount_t *mp)
{
        xfs_buf_t       *bp;
        xfs_daddr_t     d;
        int             error;

        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) {
                cmn_err(CE_WARN, "XFS: size check 1 failed");
                return XFS_ERROR(E2BIG);
        }
        error = xfs_read_buf(mp, mp->m_ddev_targp,
                             d - XFS_FSS_TO_BB(mp, 1),
                             XFS_FSS_TO_BB(mp, 1), 0, &bp);
        if (!error) {
                xfs_buf_relse(bp);
        } else {
                cmn_err(CE_WARN, "XFS: size check 2 failed");
                if (error == ENOSPC)
                        error = XFS_ERROR(E2BIG);
                return error;
        }

        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) {
                        cmn_err(CE_WARN, "XFS: size check 3 failed");
                        return XFS_ERROR(E2BIG);
                }
                error = xfs_read_buf(mp, mp->m_logdev_targp,
                                     d - XFS_FSB_TO_BB(mp, 1),
                                     XFS_FSB_TO_BB(mp, 1), 0, &bp);
                if (!error) {
                        xfs_buf_relse(bp);
                } else {
                        cmn_err(CE_WARN, "XFS: size check 3 failed");
                        if (error == ENOSPC)
                                error = XFS_ERROR(E2BIG);
                        return error;
                }
        }
        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;

#ifdef QUOTADEBUG
        xfs_fs_cmn_err(CE_NOTE, mp, "Writing superblock quota changes");
#endif

        tp = xfs_trans_alloc(mp, XFS_TRANS_QM_SBCHANGE);
        error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
                                      XFS_DEFAULT_LOG_COUNT);
        if (error) {
                xfs_trans_cancel(tp, 0);
                xfs_fs_cmn_err(CE_ALERT, mp,
                        "xfs_mount_reset_sbqflags: Superblock update failed!");
                return error;
        }

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

/*
 * 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_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)) {
                cmn_err(CE_WARN,
                        "XFS: 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);

        mp->m_maxioffset = xfs_max_file_offset(sbp->sb_blocklog);

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

        /*
         * Set the minimum read and write sizes
         */
        xfs_set_rw_sizes(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.
         */
        mp->m_inode_cluster_size = XFS_INODE_BIG_CLUSTER_SIZE;

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

        /*
         * Check that the data (and log if separate) are 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) {
                cmn_err(CE_WARN, "XFS: 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_NOFS);
        error = xfs_initialize_perag(mp, sbp->sb_agcount, &mp->m_maxagi);
        if (error) {
                cmn_err(CE_WARN, "XFS: Failed per-ag init: %d", error);
                goto out_remove_uuid;
        }

        if (!sbp->sb_logblocks) {
                cmn_err(CE_WARN, "XFS: 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) {
                cmn_err(CE_WARN, "XFS: log mount failed");
                goto out_free_perag;
        }

        /*
         * 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_free_perag;
        }

        /*
         * 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, 0);
        if (error) {
                cmn_err(CE_WARN, "XFS: failed to read root inode");
                goto out_log_dealloc;
        }

        ASSERT(rip != NULL);

        if (unlikely((rip->i_d.di_mode & S_IFMT) != S_IFDIR)) {
                cmn_err(CE_WARN, "XFS: corrupted root inode");
                cmn_err(CE_WARN, "Device %s - root %llu is not a directory",
                        XFS_BUFTARG_NAME(mp->m_ddev_targp),
                        (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.
                 */
                cmn_err(CE_WARN, "XFS: 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) {
                        cmn_err(CE_WARN, "XFS: 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) {
                        cmn_err(CE_NOTE,
                                "XFS: resetting qflags for filesystem %s",
                                mp->m_fsname);

                        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) {
                cmn_err(CE_WARN, "XFS: 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);
        }

#if defined(DEBUG) && defined(XFS_LOUD_RECOVERY)
        if (XFS_IS_QUOTA_ON(mp))
                xfs_fs_cmn_err(CE_NOTE, mp, "Disk quotas turned on");
        else
                xfs_fs_cmn_err(CE_NOTE, mp, "Disk quotas not turned on");
#endif

        /*
         * 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.
         *
         * We default to 5% or 1024 fsbs of space reserved, whichever is smaller.
         * This may drive us straight to ENOSPC on mount, but that implies
         * we were already there on the last unmount. Warn if this occurs.
         */
        resblks = mp->m_sb.sb_dblocks;
        do_div(resblks, 20);
        resblks = min_t(__uint64_t, resblks, 1024);
        error = xfs_reserve_blocks(mp, &resblks, NULL);
        if (error)
                cmn_err(CE_WARN, "XFS: Unable to allocate reserve blocks. "
                                "Continuing without a reserve pool.");

        return 0;

 out_rtunmount:
        xfs_rtunmount_inodes(mp);
 out_rele_rip:
        IRELE(rip);
 out_log_dealloc:
        xfs_log_unmount(mp);
 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;

        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_lsn_t)0, XFS_LOG_FORCE | XFS_LOG_SYNC);
        xfs_reclaim_inodes(mp, XFS_IFLUSH_ASYNC);

        xfs_qm_unmount(mp);

        /*
         * Flush out the log synchronously so that we know for sure
         * that nothing is pinned.  This is important because bflush()
         * will skip pinned buffers.
         */
        xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE | XFS_LOG_SYNC);

        xfs_binval(mp->m_ddev_targp);
        if (mp->m_rtdev_targp) {
                xfs_binval(mp->m_rtdev_targp);
        }

        /*
         * 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)
                cmn_err(CE_WARN, "XFS: Unable to free reserved block pool. "
                                "Freespace may not be correct on next mount.");

        error = xfs_log_sbcount(mp, 1);
        if (error)
                cmn_err(CE_WARN, "XFS: Unable to update superblock counters. "
                                "Freespace may not be correct on next mount.");
        xfs_unmountfs_writesb(mp);
        xfs_unmountfs_wait(mp);                 /* wait for async bufs */
        xfs_log_unmount_write(mp);
        xfs_log_unmount(mp);
        xfs_uuid_unmount(mp);

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

STATIC void
xfs_unmountfs_wait(xfs_mount_t *mp)
{
        if (mp->m_logdev_targp != mp->m_ddev_targp)
                xfs_wait_buftarg(mp->m_logdev_targp);
        if (mp->m_rtdev_targp)
                xfs_wait_buftarg(mp->m_rtdev_targp);
        xfs_wait_buftarg(mp->m_ddev_targp);
}

int
xfs_fs_writable(xfs_mount_t *mp)
{
        return !(xfs_test_for_freeze(mp) || XFS_FORCED_SHUTDOWN(mp) ||
                (mp->m_flags & XFS_MOUNT_RDONLY));
}

/*
 * xfs_log_sbcount
 *
 * Called either periodically to keep the on disk superblock values
 * roughly up to date or from unmount to make sure the values are
 * correct on a clean unmount.
 *
 * Note this code can be called during the process of freezing, so
 * we may need to use the transaction allocator which does not not
 * block when the transaction subsystem is in its frozen state.
 */
int
xfs_log_sbcount(
        xfs_mount_t     *mp,
        uint            sync)
{
        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, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
                                        XFS_DEFAULT_LOG_COUNT);
        if (error) {
                xfs_trans_cancel(tp, 0);
                return error;
        }

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

int
xfs_unmountfs_writesb(xfs_mount_t *mp)
{
        xfs_buf_t       *sbp;
        int             error = 0;

        /*
         * skip superblock write if fs is read-only, or
         * if we are doing a forced umount.
         */
        if (!((mp->m_flags & XFS_MOUNT_RDONLY) ||
                XFS_FORCED_SHUTDOWN(mp))) {

                sbp = xfs_getsb(mp, 0);

                XFS_BUF_UNDONE(sbp);
                XFS_BUF_UNREAD(sbp);
                XFS_BUF_UNDELAYWRITE(sbp);
                XFS_BUF_WRITE(sbp);
                XFS_BUF_UNASYNC(sbp);
                ASSERT(XFS_BUF_TARGET(sbp) == mp->m_ddev_targp);
                xfsbdstrat(mp, sbp);
                error = xfs_iowait(sbp);
                if (error)
                        xfs_ioerror_alert("xfs_unmountfs_writesb",
                                          mp, sbp, XFS_BUF_ADDR(sbp));
                xfs_buf_relse(sbp);
        }
        return error;
}

/*
 * xfs_mod_sb() can be used to copy arbitrary changes to the
 * in-core superblock into the superblock buffer to be logged.
 * It does not provide the higher level of locking that is
 * needed to protect the in-core superblock from concurrent
 * access.
 */
void
xfs_mod_sb(xfs_trans_t *tp, __int64_t fields)
{
        xfs_buf_t       *bp;
        int             first;
        int             last;
        xfs_mount_t     *mp;
        xfs_sb_field_t  f;

        ASSERT(fields);
        if (!fields)
                return;
        mp = tp->t_mountp;
        bp = xfs_trans_getsb(tp, mp, 0);
        first = sizeof(xfs_sb_t);
        last = 0;

        /* translate/copy */

        xfs_sb_to_disk(XFS_BUF_TO_SBP(bp), &mp->m_sb, fields);

        /* find modified range */

        f = (xfs_sb_field_t)xfs_lowbit64((__uint64_t)fields);
        ASSERT((1LL << f) & XFS_SB_MOD_BITS);
        first = xfs_sb_info[f].offset;

        f = (xfs_sb_field_t)xfs_highbit64((__uint64_t)fields);
        ASSERT((1LL << f) & XFS_SB_MOD_BITS);
        last = xfs_sb_info[f + 1].offset - 1;

        xfs_trans_log_buf(tp, bp, first, last);
}


/*
 * xfs_mod_incore_sb_unlocked() is a utility routine common 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 were out of blocks, use any available reserved blocks if
                 * were allowed to.
                 */

                        if (lcounter < 0) {
                                if (rsvd) {
                                        lcounter = (long long)mp->m_resblks_avail + delta;
                                        if (lcounter < 0) {
                                                return XFS_ERROR(ENOSPC);
                                        }
                                        mp->m_resblks_avail = lcounter;
                                        return 0;
                                } else {        /* not reserved */
                                        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(
        xfs_mount_t     *mp,
        xfs_sb_field_t  field,
        int64_t         delta,
        int             rsvd)
{
        int     status;

        /* check for per-cpu counters */
        switch (field) {
#ifdef HAVE_PERCPU_SB
        case XFS_SBS_ICOUNT:
        case XFS_SBS_IFREE:
        case XFS_SBS_FDBLOCKS:
                if (!(mp->m_flags & XFS_MOUNT_NO_PERCPU_SB)) {
                        status = xfs_icsb_modify_counters(mp, field,
                                                        delta, rsvd);
                        break;
                }
                /* FALLTHROUGH */
#endif
        default:
                spin_lock(&mp->m_sb_lock);
                status = xfs_mod_incore_sb_unlocked(mp, field, delta, rsvd);
                spin_unlock(&mp->m_sb_lock);
                break;
        }

        return status;
}

/*
 * xfs_mod_incore_sb_batch() is used to change more than one field
 * in the in-core superblock structure at a time.  This modification
 * is protected by a lock internal to this module.  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.
 */
int
xfs_mod_incore_sb_batch(xfs_mount_t *mp, xfs_mod_sb_t *msb, uint nmsb, int rsvd)
{
        int             status=0;
        xfs_mod_sb_t    *msbp;

        /*
         * 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);
        msbp = &msb[0];
        for (msbp = &msbp[0]; msbp < (msb + nmsb); msbp++) {
                /*
                 * Apply the delta at index n.  If it fails, break
                 * from the loop so we'll fall into the undo loop
                 * below.
                 */
                switch (msbp->msb_field) {
#ifdef HAVE_PERCPU_SB
                case XFS_SBS_ICOUNT:
                case XFS_SBS_IFREE:
                case XFS_SBS_FDBLOCKS:
                        if (!(mp->m_flags & XFS_MOUNT_NO_PERCPU_SB)) {
                                spin_unlock(&mp->m_sb_lock);
                                status = xfs_icsb_modify_counters(mp,
                                                        msbp->msb_field,
                                                        msbp->msb_delta, rsvd);
                                spin_lock(&mp->m_sb_lock);
                                break;
                        }
                        /* FALLTHROUGH */
#endif
                default:
                        status = xfs_mod_incore_sb_unlocked(mp,
                                                msbp->msb_field,
                                                msbp->msb_delta, rsvd);
                        break;
                }

                if (status != 0) {
                        break;
                }
        }

        /*
         * If we didn't complete the loop above, then back out
         * any changes made to the superblock.  If you add code
         * between the loop above and here, make sure that you
         * preserve the value of status. Loop back until
         * we step below the beginning of the array.  Make sure
         * we don't touch anything back there.
         */
        if (status != 0) {
                msbp--;
                while (msbp >= msb) {
                        switch (msbp->msb_field) {
#ifdef HAVE_PERCPU_SB
                        case XFS_SBS_ICOUNT:
                        case XFS_SBS_IFREE:
                        case XFS_SBS_FDBLOCKS:
                                if (!(mp->m_flags & XFS_MOUNT_NO_PERCPU_SB)) {
                                        spin_unlock(&mp->m_sb_lock);
                                        status = xfs_icsb_modify_counters(mp,
                                                        msbp->msb_field,
                                                        -(msbp->msb_delta),
                                                        rsvd);
                                        spin_lock(&mp->m_sb_lock);
                                        break;
                                }
                                /* FALLTHROUGH */
#endif
                        default:
                                status = xfs_mod_incore_sb_unlocked(mp,
                                                        msbp->msb_field,
                                                        -(msbp->msb_delta),
                                                        rsvd);
                                break;
                        }
                        ASSERT(status == 0);
                        msbp--;
                }
        }
        spin_unlock(&mp->m_sb_lock);
        return status;
}

/*
 * 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.
 */
xfs_buf_t *
xfs_getsb(
        xfs_mount_t     *mp,
        int             flags)
{
        xfs_buf_t       *bp;

        ASSERT(mp->m_sb_bp != NULL);
        bp = mp->m_sb_bp;
        if (flags & XFS_BUF_TRYLOCK) {
                if (!XFS_BUF_CPSEMA(bp)) {
                        return NULL;
                }
        } else {
                XFS_BUF_PSEMA(bp, PRIBIO);
        }
        XFS_BUF_HOLD(bp);
        ASSERT(XFS_BUF_ISDONE(bp));
        return bp;
}

/*
 * Used to free the superblock along various error paths.
 */
void
xfs_freesb(
        xfs_mount_t     *mp)
{
        xfs_buf_t       *bp;

        /*
         * Use xfs_getsb() so that the buffer will be locked
         * when we call xfs_buf_relse().
         */
        bp = xfs_getsb(mp, 0);
        XFS_BUF_UNMANAGE(bp);
        xfs_buf_relse(bp);
        mp->m_sb_bp = NULL;
}

/*
 * 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, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
                                XFS_DEFAULT_LOG_COUNT);
        if (error) {
                xfs_trans_cancel(tp, 0);
                return error;
        }
        xfs_mod_sb(tp, fields);
        error = xfs_trans_commit(tp, 0);
        return error;
}


#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;

#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 */

        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;
        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);
}

STATIC 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