ext4: convert instrumentation from markers to tracepoints

[linux-2.6/mini2440.git] / fs / ext4 / ialloc.c

/*
 *  linux/fs/ext4/ialloc.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  BSD ufs-inspired inode and directory allocation by
 *  Stephen Tweedie (sct@redhat.com), 1993
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd2.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/quotaops.h>
#include <linux/buffer_head.h>
#include <linux/random.h>
#include <linux/bitops.h>
#include <linux/blkdev.h>
#include <asm/byteorder.h>

#include "ext4.h"
#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"

#include <trace/events/ext4.h>

/*
 * ialloc.c contains the inodes allocation and deallocation routines
 */

/*
 * The free inodes are managed by bitmaps.  A file system contains several
 * blocks groups.  Each group contains 1 bitmap block for blocks, 1 bitmap
 * block for inodes, N blocks for the inode table and data blocks.
 *
 * The file system contains group descriptors which are located after the
 * super block.  Each descriptor contains the number of the bitmap block and
 * the free blocks count in the block.
 */

/*
 * To avoid calling the atomic setbit hundreds or thousands of times, we only
 * need to use it within a single byte (to ensure we get endianness right).
 * We can use memset for the rest of the bitmap as there are no other users.
 */
void mark_bitmap_end(int start_bit, int end_bit, char *bitmap)
{
        int i;

        if (start_bit >= end_bit)
                return;

        ext4_debug("mark end bits +%d through +%d used\n", start_bit, end_bit);
        for (i = start_bit; i < ((start_bit + 7) & ~7UL); i++)
                ext4_set_bit(i, bitmap);
        if (i < end_bit)
                memset(bitmap + (i >> 3), 0xff, (end_bit - i) >> 3);
}

/* Initializes an uninitialized inode bitmap */
unsigned ext4_init_inode_bitmap(struct super_block *sb, struct buffer_head *bh,
                                ext4_group_t block_group,
                                struct ext4_group_desc *gdp)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);

        J_ASSERT_BH(bh, buffer_locked(bh));

        /* If checksum is bad mark all blocks and inodes use to prevent
         * allocation, essentially implementing a per-group read-only flag. */
        if (!ext4_group_desc_csum_verify(sbi, block_group, gdp)) {
                ext4_error(sb, __func__, "Checksum bad for group %u",
                           block_group);
                ext4_free_blks_set(sb, gdp, 0);
                ext4_free_inodes_set(sb, gdp, 0);
                ext4_itable_unused_set(sb, gdp, 0);
                memset(bh->b_data, 0xff, sb->s_blocksize);
                return 0;
        }

        memset(bh->b_data, 0, (EXT4_INODES_PER_GROUP(sb) + 7) / 8);
        mark_bitmap_end(EXT4_INODES_PER_GROUP(sb), sb->s_blocksize * 8,
                        bh->b_data);

        return EXT4_INODES_PER_GROUP(sb);
}

/*
 * Read the inode allocation bitmap for a given block_group, reading
 * into the specified slot in the superblock's bitmap cache.
 *
 * Return buffer_head of bitmap on success or NULL.
 */
static struct buffer_head *
ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
{
        struct ext4_group_desc *desc;
        struct buffer_head *bh = NULL;
        ext4_fsblk_t bitmap_blk;

        desc = ext4_get_group_desc(sb, block_group, NULL);
        if (!desc)
                return NULL;
        bitmap_blk = ext4_inode_bitmap(sb, desc);
        bh = sb_getblk(sb, bitmap_blk);
        if (unlikely(!bh)) {
                ext4_error(sb, __func__,
                            "Cannot read inode bitmap - "
                            "block_group = %u, inode_bitmap = %llu",
                            block_group, bitmap_blk);
                return NULL;
        }
        if (bitmap_uptodate(bh))
                return bh;

        lock_buffer(bh);
        if (bitmap_uptodate(bh)) {
                unlock_buffer(bh);
                return bh;
        }
        ext4_lock_group(sb, block_group);
        if (desc->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
                ext4_init_inode_bitmap(sb, bh, block_group, desc);
                set_bitmap_uptodate(bh);
                set_buffer_uptodate(bh);
                ext4_unlock_group(sb, block_group);
                unlock_buffer(bh);
                return bh;
        }
        ext4_unlock_group(sb, block_group);
        if (buffer_uptodate(bh)) {
                /*
                 * if not uninit if bh is uptodate,
                 * bitmap is also uptodate
                 */
                set_bitmap_uptodate(bh);
                unlock_buffer(bh);
                return bh;
        }
        /*
         * submit the buffer_head for read. We can
         * safely mark the bitmap as uptodate now.
         * We do it here so the bitmap uptodate bit
         * get set with buffer lock held.
         */
        set_bitmap_uptodate(bh);
        if (bh_submit_read(bh) < 0) {
                put_bh(bh);
                ext4_error(sb, __func__,
                            "Cannot read inode bitmap - "
                            "block_group = %u, inode_bitmap = %llu",
                            block_group, bitmap_blk);
                return NULL;
        }
        return bh;
}

/*
 * NOTE! When we get the inode, we're the only people
 * that have access to it, and as such there are no
 * race conditions we have to worry about. The inode
 * is not on the hash-lists, and it cannot be reached
 * through the filesystem because the directory entry
 * has been deleted earlier.
 *
 * HOWEVER: we must make sure that we get no aliases,
 * which means that we have to call "clear_inode()"
 * _before_ we mark the inode not in use in the inode
 * bitmaps. Otherwise a newly created file might use
 * the same inode number (not actually the same pointer
 * though), and then we'd have two inodes sharing the
 * same inode number and space on the harddisk.
 */
void ext4_free_inode(handle_t *handle, struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        int is_directory;
        unsigned long ino;
        struct buffer_head *bitmap_bh = NULL;
        struct buffer_head *bh2;
        ext4_group_t block_group;
        unsigned long bit;
        struct ext4_group_desc *gdp;
        struct ext4_super_block *es;
        struct ext4_sb_info *sbi;
        int fatal = 0, err, count, cleared;

        if (atomic_read(&inode->i_count) > 1) {
                printk(KERN_ERR "ext4_free_inode: inode has count=%d\n",
                       atomic_read(&inode->i_count));
                return;
        }
        if (inode->i_nlink) {
                printk(KERN_ERR "ext4_free_inode: inode has nlink=%d\n",
                       inode->i_nlink);
                return;
        }
        if (!sb) {
                printk(KERN_ERR "ext4_free_inode: inode on "
                       "nonexistent device\n");
                return;
        }
        sbi = EXT4_SB(sb);

        ino = inode->i_ino;
        ext4_debug("freeing inode %lu\n", ino);
        trace_ext4_free_inode(inode);

        /*
         * Note: we must free any quota before locking the superblock,
         * as writing the quota to disk may need the lock as well.
         */
        vfs_dq_init(inode);
        ext4_xattr_delete_inode(handle, inode);
        vfs_dq_free_inode(inode);
        vfs_dq_drop(inode);

        is_directory = S_ISDIR(inode->i_mode);

        /* Do this BEFORE marking the inode not in use or returning an error */
        clear_inode(inode);

        es = EXT4_SB(sb)->s_es;
        if (ino < EXT4_FIRST_INO(sb) || ino > le32_to_cpu(es->s_inodes_count)) {
                ext4_error(sb, "ext4_free_inode",
                           "reserved or nonexistent inode %lu", ino);
                goto error_return;
        }
        block_group = (ino - 1) / EXT4_INODES_PER_GROUP(sb);
        bit = (ino - 1) % EXT4_INODES_PER_GROUP(sb);
        bitmap_bh = ext4_read_inode_bitmap(sb, block_group);
        if (!bitmap_bh)
                goto error_return;

        BUFFER_TRACE(bitmap_bh, "get_write_access");
        fatal = ext4_journal_get_write_access(handle, bitmap_bh);
        if (fatal)
                goto error_return;

        /* Ok, now we can actually update the inode bitmaps.. */
        cleared = ext4_clear_bit_atomic(ext4_group_lock_ptr(sb, block_group),
                                        bit, bitmap_bh->b_data);
        if (!cleared)
                ext4_error(sb, "ext4_free_inode",
                           "bit already cleared for inode %lu", ino);
        else {
                gdp = ext4_get_group_desc(sb, block_group, &bh2);

                BUFFER_TRACE(bh2, "get_write_access");
                fatal = ext4_journal_get_write_access(handle, bh2);
                if (fatal) goto error_return;

                if (gdp) {
                        ext4_lock_group(sb, block_group);
                        count = ext4_free_inodes_count(sb, gdp) + 1;
                        ext4_free_inodes_set(sb, gdp, count);
                        if (is_directory) {
                                count = ext4_used_dirs_count(sb, gdp) - 1;
                                ext4_used_dirs_set(sb, gdp, count);
                                if (sbi->s_log_groups_per_flex) {
                                        ext4_group_t f;

                                        f = ext4_flex_group(sbi, block_group);
                                        atomic_dec(&sbi->s_flex_groups[f].free_inodes);
                                }

                        }
                        gdp->bg_checksum = ext4_group_desc_csum(sbi,
                                                        block_group, gdp);
                        ext4_unlock_group(sb, block_group);
                        percpu_counter_inc(&sbi->s_freeinodes_counter);
                        if (is_directory)
                                percpu_counter_dec(&sbi->s_dirs_counter);

                        if (sbi->s_log_groups_per_flex) {
                                ext4_group_t f;

                                f = ext4_flex_group(sbi, block_group);
                                atomic_inc(&sbi->s_flex_groups[f].free_inodes);
                        }
                }
                BUFFER_TRACE(bh2, "call ext4_handle_dirty_metadata");
                err = ext4_handle_dirty_metadata(handle, NULL, bh2);
                if (!fatal) fatal = err;
        }
        BUFFER_TRACE(bitmap_bh, "call ext4_handle_dirty_metadata");
        err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
        if (!fatal)
                fatal = err;
        sb->s_dirt = 1;
error_return:
        brelse(bitmap_bh);
        ext4_std_error(sb, fatal);
}

/*
 * There are two policies for allocating an inode.  If the new inode is
 * a directory, then a forward search is made for a block group with both
 * free space and a low directory-to-inode ratio; if that fails, then of
 * the groups with above-average free space, that group with the fewest
 * directories already is chosen.
 *
 * For other inodes, search forward from the parent directory\'s block
 * group to find a free inode.
 */
static int find_group_dir(struct super_block *sb, struct inode *parent,
                                ext4_group_t *best_group)
{
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        unsigned int freei, avefreei;
        struct ext4_group_desc *desc, *best_desc = NULL;
        ext4_group_t group;
        int ret = -1;

        freei = percpu_counter_read_positive(&EXT4_SB(sb)->s_freeinodes_counter);
        avefreei = freei / ngroups;

        for (group = 0; group < ngroups; group++) {
                desc = ext4_get_group_desc(sb, group, NULL);
                if (!desc || !ext4_free_inodes_count(sb, desc))
                        continue;
                if (ext4_free_inodes_count(sb, desc) < avefreei)
                        continue;
                if (!best_desc ||
                    (ext4_free_blks_count(sb, desc) >
                     ext4_free_blks_count(sb, best_desc))) {
                        *best_group = group;
                        best_desc = desc;
                        ret = 0;
                }
        }
        return ret;
}

#define free_block_ratio 10

static int find_group_flex(struct super_block *sb, struct inode *parent,
                           ext4_group_t *best_group)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_group_desc *desc;
        struct flex_groups *flex_group = sbi->s_flex_groups;
        ext4_group_t parent_group = EXT4_I(parent)->i_block_group;
        ext4_group_t parent_fbg_group = ext4_flex_group(sbi, parent_group);
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        int flex_size = ext4_flex_bg_size(sbi);
        ext4_group_t best_flex = parent_fbg_group;
        int blocks_per_flex = sbi->s_blocks_per_group * flex_size;
        int flexbg_free_blocks;
        int flex_freeb_ratio;
        ext4_group_t n_fbg_groups;
        ext4_group_t i;

        n_fbg_groups = (ngroups + flex_size - 1) >>
                sbi->s_log_groups_per_flex;

find_close_to_parent:
        flexbg_free_blocks = atomic_read(&flex_group[best_flex].free_blocks);
        flex_freeb_ratio = flexbg_free_blocks * 100 / blocks_per_flex;
        if (atomic_read(&flex_group[best_flex].free_inodes) &&
            flex_freeb_ratio > free_block_ratio)
                goto found_flexbg;

        if (best_flex && best_flex == parent_fbg_group) {
                best_flex--;
                goto find_close_to_parent;
        }

        for (i = 0; i < n_fbg_groups; i++) {
                if (i == parent_fbg_group || i == parent_fbg_group - 1)
                        continue;

                flexbg_free_blocks = atomic_read(&flex_group[i].free_blocks);
                flex_freeb_ratio = flexbg_free_blocks * 100 / blocks_per_flex;

                if (flex_freeb_ratio > free_block_ratio &&
                    (atomic_read(&flex_group[i].free_inodes))) {
                        best_flex = i;
                        goto found_flexbg;
                }

                if ((atomic_read(&flex_group[best_flex].free_inodes) == 0) ||
                    ((atomic_read(&flex_group[i].free_blocks) >
                      atomic_read(&flex_group[best_flex].free_blocks)) &&
                     atomic_read(&flex_group[i].free_inodes)))
                        best_flex = i;
        }

        if (!atomic_read(&flex_group[best_flex].free_inodes) ||
            !atomic_read(&flex_group[best_flex].free_blocks))
                return -1;

found_flexbg:
        for (i = best_flex * flex_size; i < ngroups &&
                     i < (best_flex + 1) * flex_size; i++) {
                desc = ext4_get_group_desc(sb, i, NULL);
                if (ext4_free_inodes_count(sb, desc)) {
                        *best_group = i;
                        goto out;
                }
        }

        return -1;
out:
        return 0;
}

struct orlov_stats {
        __u32 free_inodes;
        __u32 free_blocks;
        __u32 used_dirs;
};

/*
 * Helper function for Orlov's allocator; returns critical information
 * for a particular block group or flex_bg.  If flex_size is 1, then g
 * is a block group number; otherwise it is flex_bg number.
 */
void get_orlov_stats(struct super_block *sb, ext4_group_t g,
                       int flex_size, struct orlov_stats *stats)
{
        struct ext4_group_desc *desc;
        struct flex_groups *flex_group = EXT4_SB(sb)->s_flex_groups;

        if (flex_size > 1) {
                stats->free_inodes = atomic_read(&flex_group[g].free_inodes);
                stats->free_blocks = atomic_read(&flex_group[g].free_blocks);
                stats->used_dirs = atomic_read(&flex_group[g].used_dirs);
                return;
        }

        desc = ext4_get_group_desc(sb, g, NULL);
        if (desc) {
                stats->free_inodes = ext4_free_inodes_count(sb, desc);
                stats->free_blocks = ext4_free_blks_count(sb, desc);
                stats->used_dirs = ext4_used_dirs_count(sb, desc);
        } else {
                stats->free_inodes = 0;
                stats->free_blocks = 0;
                stats->used_dirs = 0;
        }
}

/*
 * Orlov's allocator for directories.
 *
 * We always try to spread first-level directories.
 *
 * If there are blockgroups with both free inodes and free blocks counts
 * not worse than average we return one with smallest directory count.
 * Otherwise we simply return a random group.
 *
 * For the rest rules look so:
 *
 * It's OK to put directory into a group unless
 * it has too many directories already (max_dirs) or
 * it has too few free inodes left (min_inodes) or
 * it has too few free blocks left (min_blocks) or
 * Parent's group is preferred, if it doesn't satisfy these
 * conditions we search cyclically through the rest. If none
 * of the groups look good we just look for a group with more
 * free inodes than average (starting at parent's group).
 */

static int find_group_orlov(struct super_block *sb, struct inode *parent,
                            ext4_group_t *group, int mode)
{
        ext4_group_t parent_group = EXT4_I(parent)->i_block_group;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_group_t real_ngroups = ext4_get_groups_count(sb);
        int inodes_per_group = EXT4_INODES_PER_GROUP(sb);
        unsigned int freei, avefreei;
        ext4_fsblk_t freeb, avefreeb;
        unsigned int ndirs;
        int max_dirs, min_inodes;
        ext4_grpblk_t min_blocks;
        ext4_group_t i, grp, g, ngroups;
        struct ext4_group_desc *desc;
        struct orlov_stats stats;
        int flex_size = ext4_flex_bg_size(sbi);

        ngroups = real_ngroups;
        if (flex_size > 1) {
                ngroups = (real_ngroups + flex_size - 1) >>
                        sbi->s_log_groups_per_flex;
                parent_group >>= sbi->s_log_groups_per_flex;
        }

        freei = percpu_counter_read_positive(&sbi->s_freeinodes_counter);
        avefreei = freei / ngroups;
        freeb = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
        avefreeb = freeb;
        do_div(avefreeb, ngroups);
        ndirs = percpu_counter_read_positive(&sbi->s_dirs_counter);

        if (S_ISDIR(mode) &&
            ((parent == sb->s_root->d_inode) ||
             (EXT4_I(parent)->i_flags & EXT4_TOPDIR_FL))) {
                int best_ndir = inodes_per_group;
                int ret = -1;

                get_random_bytes(&grp, sizeof(grp));
                parent_group = (unsigned)grp % ngroups;
                for (i = 0; i < ngroups; i++) {
                        g = (parent_group + i) % ngroups;
                        get_orlov_stats(sb, g, flex_size, &stats);
                        if (!stats.free_inodes)
                                continue;
                        if (stats.used_dirs >= best_ndir)
                                continue;
                        if (stats.free_inodes < avefreei)
                                continue;
                        if (stats.free_blocks < avefreeb)
                                continue;
                        grp = g;
                        ret = 0;
                        best_ndir = stats.used_dirs;
                }
                if (ret)
                        goto fallback;
        found_flex_bg:
                if (flex_size == 1) {
                        *group = grp;
                        return 0;
                }

                /*
                 * We pack inodes at the beginning of the flexgroup's
                 * inode tables.  Block allocation decisions will do
                 * something similar, although regular files will
                 * start at 2nd block group of the flexgroup.  See
                 * ext4_ext_find_goal() and ext4_find_near().
                 */
                grp *= flex_size;
                for (i = 0; i < flex_size; i++) {
                        if (grp+i >= real_ngroups)
                                break;
                        desc = ext4_get_group_desc(sb, grp+i, NULL);
                        if (desc && ext4_free_inodes_count(sb, desc)) {
                                *group = grp+i;
                                return 0;
                        }
                }
                goto fallback;
        }

        max_dirs = ndirs / ngroups + inodes_per_group / 16;
        min_inodes = avefreei - inodes_per_group*flex_size / 4;
        if (min_inodes < 1)
                min_inodes = 1;
        min_blocks = avefreeb - EXT4_BLOCKS_PER_GROUP(sb)*flex_size / 4;

        /*
         * Start looking in the flex group where we last allocated an
         * inode for this parent directory
         */
        if (EXT4_I(parent)->i_last_alloc_group != ~0) {
                parent_group = EXT4_I(parent)->i_last_alloc_group;
                if (flex_size > 1)
                        parent_group >>= sbi->s_log_groups_per_flex;
        }

        for (i = 0; i < ngroups; i++) {
                grp = (parent_group + i) % ngroups;
                get_orlov_stats(sb, grp, flex_size, &stats);
                if (stats.used_dirs >= max_dirs)
                        continue;
                if (stats.free_inodes < min_inodes)
                        continue;
                if (stats.free_blocks < min_blocks)
                        continue;
                goto found_flex_bg;
        }

fallback:
        ngroups = real_ngroups;
        avefreei = freei / ngroups;
fallback_retry:
        parent_group = EXT4_I(parent)->i_block_group;
        for (i = 0; i < ngroups; i++) {
                grp = (parent_group + i) % ngroups;
                desc = ext4_get_group_desc(sb, grp, NULL);
                if (desc && ext4_free_inodes_count(sb, desc) &&
                    ext4_free_inodes_count(sb, desc) >= avefreei) {
                        *group = grp;
                        return 0;
                }
        }

        if (avefreei) {
                /*
                 * The free-inodes counter is approximate, and for really small
                 * filesystems the above test can fail to find any blockgroups
                 */
                avefreei = 0;
                goto fallback_retry;
        }

        return -1;
}

static int find_group_other(struct super_block *sb, struct inode *parent,
                            ext4_group_t *group, int mode)
{
        ext4_group_t parent_group = EXT4_I(parent)->i_block_group;
        ext4_group_t i, last, ngroups = ext4_get_groups_count(sb);
        struct ext4_group_desc *desc;
        int flex_size = ext4_flex_bg_size(EXT4_SB(sb));

        /*
         * Try to place the inode is the same flex group as its
         * parent.  If we can't find space, use the Orlov algorithm to
         * find another flex group, and store that information in the
         * parent directory's inode information so that use that flex
         * group for future allocations.
         */
        if (flex_size > 1) {
                int retry = 0;

        try_again:
                parent_group &= ~(flex_size-1);
                last = parent_group + flex_size;
                if (last > ngroups)
                        last = ngroups;
                for  (i = parent_group; i < last; i++) {
                        desc = ext4_get_group_desc(sb, i, NULL);
                        if (desc && ext4_free_inodes_count(sb, desc)) {
                                *group = i;
                                return 0;
                        }
                }
                if (!retry && EXT4_I(parent)->i_last_alloc_group != ~0) {
                        retry = 1;
                        parent_group = EXT4_I(parent)->i_last_alloc_group;
                        goto try_again;
                }
                /*
                 * If this didn't work, use the Orlov search algorithm
                 * to find a new flex group; we pass in the mode to
                 * avoid the topdir algorithms.
                 */
                *group = parent_group + flex_size;
                if (*group > ngroups)
                        *group = 0;
                return find_group_orlov(sb, parent, group, mode);
        }

        /*
         * Try to place the inode in its parent directory
         */
        *group = parent_group;
        desc = ext4_get_group_desc(sb, *group, NULL);
        if (desc && ext4_free_inodes_count(sb, desc) &&
                        ext4_free_blks_count(sb, desc))
                return 0;

        /*
         * We're going to place this inode in a different blockgroup from its
         * parent.  We want to cause files in a common directory to all land in
         * the same blockgroup.  But we want files which are in a different
         * directory which shares a blockgroup with our parent to land in a
         * different blockgroup.
         *
         * So add our directory's i_ino into the starting point for the hash.
         */
        *group = (*group + parent->i_ino) % ngroups;

        /*
         * Use a quadratic hash to find a group with a free inode and some free
         * blocks.
         */
        for (i = 1; i < ngroups; i <<= 1) {
                *group += i;
                if (*group >= ngroups)
                        *group -= ngroups;
                desc = ext4_get_group_desc(sb, *group, NULL);
                if (desc && ext4_free_inodes_count(sb, desc) &&
                                ext4_free_blks_count(sb, desc))
                        return 0;
        }

        /*
         * That failed: try linear search for a free inode, even if that group
         * has no free blocks.
         */
        *group = parent_group;
        for (i = 0; i < ngroups; i++) {
                if (++*group >= ngroups)
                        *group = 0;
                desc = ext4_get_group_desc(sb, *group, NULL);
                if (desc && ext4_free_inodes_count(sb, desc))
                        return 0;
        }

        return -1;
}

/*
 * claim the inode from the inode bitmap. If the group
 * is uninit we need to take the groups's ext4_group_lock
 * and clear the uninit flag. The inode bitmap update
 * and group desc uninit flag clear should be done
 * after holding ext4_group_lock so that ext4_read_inode_bitmap
 * doesn't race with the ext4_claim_inode
 */
static int ext4_claim_inode(struct super_block *sb,
                        struct buffer_head *inode_bitmap_bh,
                        unsigned long ino, ext4_group_t group, int mode)
{
        int free = 0, retval = 0, count;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, NULL);

        ext4_lock_group(sb, group);
        if (ext4_set_bit(ino, inode_bitmap_bh->b_data)) {
                /* not a free inode */
                retval = 1;
                goto err_ret;
        }
        ino++;
        if ((group == 0 && ino < EXT4_FIRST_INO(sb)) ||
                        ino > EXT4_INODES_PER_GROUP(sb)) {
                ext4_unlock_group(sb, group);
                ext4_error(sb, __func__,
                           "reserved inode or inode > inodes count - "
                           "block_group = %u, inode=%lu", group,
                           ino + group * EXT4_INODES_PER_GROUP(sb));
                return 1;
        }
        /* If we didn't allocate from within the initialized part of the inode
         * table then we need to initialize up to this inode. */
        if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {

                if (gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
                        gdp->bg_flags &= cpu_to_le16(~EXT4_BG_INODE_UNINIT);
                        /* When marking the block group with
                         * ~EXT4_BG_INODE_UNINIT we don't want to depend
                         * on the value of bg_itable_unused even though
                         * mke2fs could have initialized the same for us.
                         * Instead we calculated the value below
                         */

                        free = 0;
                } else {
                        free = EXT4_INODES_PER_GROUP(sb) -
                                ext4_itable_unused_count(sb, gdp);
                }

                /*
                 * Check the relative inode number against the last used
                 * relative inode number in this group. if it is greater
                 * we need to  update the bg_itable_unused count
                 *
                 */
                if (ino > free)
                        ext4_itable_unused_set(sb, gdp,
                                        (EXT4_INODES_PER_GROUP(sb) - ino));
        }
        count = ext4_free_inodes_count(sb, gdp) - 1;
        ext4_free_inodes_set(sb, gdp, count);
        if (S_ISDIR(mode)) {
                count = ext4_used_dirs_count(sb, gdp) + 1;
                ext4_used_dirs_set(sb, gdp, count);
                if (sbi->s_log_groups_per_flex) {
                        ext4_group_t f = ext4_flex_group(sbi, group);

                        atomic_inc(&sbi->s_flex_groups[f].free_inodes);
                }
        }
        gdp->bg_checksum = ext4_group_desc_csum(sbi, group, gdp);
err_ret:
        ext4_unlock_group(sb, group);
        return retval;
}

/*
 * There are two policies for allocating an inode.  If the new inode is
 * a directory, then a forward search is made for a block group with both
 * free space and a low directory-to-inode ratio; if that fails, then of
 * the groups with above-average free space, that group with the fewest
 * directories already is chosen.
 *
 * For other inodes, search forward from the parent directory's block
 * group to find a free inode.
 */
struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode)
{
        struct super_block *sb;
        struct buffer_head *inode_bitmap_bh = NULL;
        struct buffer_head *group_desc_bh;
        ext4_group_t ngroups, group = 0;
        unsigned long ino = 0;
        struct inode *inode;
        struct ext4_group_desc *gdp = NULL;
        struct ext4_inode_info *ei;
        struct ext4_sb_info *sbi;
        int ret2, err = 0;
        struct inode *ret;
        ext4_group_t i;
        int free = 0;
        static int once = 1;
        ext4_group_t flex_group;

        /* Cannot create files in a deleted directory */
        if (!dir || !dir->i_nlink)
                return ERR_PTR(-EPERM);

        sb = dir->i_sb;
        ngroups = ext4_get_groups_count(sb);
        trace_ext4_request_inode(dir, mode);
        inode = new_inode(sb);
        if (!inode)
                return ERR_PTR(-ENOMEM);
        ei = EXT4_I(inode);
        sbi = EXT4_SB(sb);

        if (sbi->s_log_groups_per_flex && test_opt(sb, OLDALLOC)) {
                ret2 = find_group_flex(sb, dir, &group);
                if (ret2 == -1) {
                        ret2 = find_group_other(sb, dir, &group, mode);
                        if (ret2 == 0 && once) {
                                once = 0;
                                printk(KERN_NOTICE "ext4: find_group_flex "
                                       "failed, fallback succeeded dir %lu\n",
                                       dir->i_ino);
                        }
                }
                goto got_group;
        }

        if (S_ISDIR(mode)) {
                if (test_opt(sb, OLDALLOC))
                        ret2 = find_group_dir(sb, dir, &group);
                else
                        ret2 = find_group_orlov(sb, dir, &group, mode);
        } else
                ret2 = find_group_other(sb, dir, &group, mode);

got_group:
        EXT4_I(dir)->i_last_alloc_group = group;
        err = -ENOSPC;
        if (ret2 == -1)
                goto out;

        for (i = 0; i < ngroups; i++) {
                err = -EIO;

                gdp = ext4_get_group_desc(sb, group, &group_desc_bh);
                if (!gdp)
                        goto fail;

                brelse(inode_bitmap_bh);
                inode_bitmap_bh = ext4_read_inode_bitmap(sb, group);
                if (!inode_bitmap_bh)
                        goto fail;

                ino = 0;

repeat_in_this_group:
                ino = ext4_find_next_zero_bit((unsigned long *)
                                              inode_bitmap_bh->b_data,
                                              EXT4_INODES_PER_GROUP(sb), ino);

                if (ino < EXT4_INODES_PER_GROUP(sb)) {

                        BUFFER_TRACE(inode_bitmap_bh, "get_write_access");
                        err = ext4_journal_get_write_access(handle,
                                                            inode_bitmap_bh);
                        if (err)
                                goto fail;

                        BUFFER_TRACE(group_desc_bh, "get_write_access");
                        err = ext4_journal_get_write_access(handle,
                                                                group_desc_bh);
                        if (err)
                                goto fail;
                        if (!ext4_claim_inode(sb, inode_bitmap_bh,
                                                ino, group, mode)) {
                                /* we won it */
                                BUFFER_TRACE(inode_bitmap_bh,
                                        "call ext4_handle_dirty_metadata");
                                err = ext4_handle_dirty_metadata(handle,
                                                                 inode,
                                                        inode_bitmap_bh);
                                if (err)
                                        goto fail;
                                /* zero bit is inode number 1*/
                                ino++;
                                goto got;
                        }
                        /* we lost it */
                        ext4_handle_release_buffer(handle, inode_bitmap_bh);
                        ext4_handle_release_buffer(handle, group_desc_bh);

                        if (++ino < EXT4_INODES_PER_GROUP(sb))
                                goto repeat_in_this_group;
                }

                /*
                 * This case is possible in concurrent environment.  It is very
                 * rare.  We cannot repeat the find_group_xxx() call because
                 * that will simply return the same blockgroup, because the
                 * group descriptor metadata has not yet been updated.
                 * So we just go onto the next blockgroup.
                 */
                if (++group == ngroups)
                        group = 0;
        }
        err = -ENOSPC;
        goto out;

got:
        /* We may have to initialize the block bitmap if it isn't already */
        if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM) &&
            gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
                struct buffer_head *block_bitmap_bh;

                block_bitmap_bh = ext4_read_block_bitmap(sb, group);
                BUFFER_TRACE(block_bitmap_bh, "get block bitmap access");
                err = ext4_journal_get_write_access(handle, block_bitmap_bh);
                if (err) {
                        brelse(block_bitmap_bh);
                        goto fail;
                }

                free = 0;
                ext4_lock_group(sb, group);
                /* recheck and clear flag under lock if we still need to */
                if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
                        free = ext4_free_blocks_after_init(sb, group, gdp);
                        gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
                        ext4_free_blks_set(sb, gdp, free);
                        gdp->bg_checksum = ext4_group_desc_csum(sbi, group,
                                                                gdp);
                }
                ext4_unlock_group(sb, group);

                /* Don't need to dirty bitmap block if we didn't change it */
                if (free) {
                        BUFFER_TRACE(block_bitmap_bh, "dirty block bitmap");
                        err = ext4_handle_dirty_metadata(handle,
                                                        NULL, block_bitmap_bh);
                }

                brelse(block_bitmap_bh);
                if (err)
                        goto fail;
        }
        BUFFER_TRACE(group_desc_bh, "call ext4_handle_dirty_metadata");
        err = ext4_handle_dirty_metadata(handle, NULL, group_desc_bh);
        if (err)
                goto fail;

        percpu_counter_dec(&sbi->s_freeinodes_counter);
        if (S_ISDIR(mode))
                percpu_counter_inc(&sbi->s_dirs_counter);
        sb->s_dirt = 1;

        if (sbi->s_log_groups_per_flex) {
                flex_group = ext4_flex_group(sbi, group);
                atomic_dec(&sbi->s_flex_groups[flex_group].free_inodes);
        }

        inode->i_uid = current_fsuid();
        if (test_opt(sb, GRPID))
                inode->i_gid = dir->i_gid;
        else if (dir->i_mode & S_ISGID) {
                inode->i_gid = dir->i_gid;
                if (S_ISDIR(mode))
                        mode |= S_ISGID;
        } else
                inode->i_gid = current_fsgid();
        inode->i_mode = mode;

        inode->i_ino = ino + group * EXT4_INODES_PER_GROUP(sb);
        /* This is the optimal IO size (for stat), not the fs block size */
        inode->i_blocks = 0;
        inode->i_mtime = inode->i_atime = inode->i_ctime = ei->i_crtime =
                                                       ext4_current_time(inode);

        memset(ei->i_data, 0, sizeof(ei->i_data));
        ei->i_dir_start_lookup = 0;
        ei->i_disksize = 0;

        /*
         * Don't inherit extent flag from directory, amongst others. We set
         * extent flag on newly created directory and file only if -o extent
         * mount option is specified
         */
        ei->i_flags =
                ext4_mask_flags(mode, EXT4_I(dir)->i_flags & EXT4_FL_INHERITED);
        ei->i_file_acl = 0;
        ei->i_dtime = 0;
        ei->i_block_group = group;
        ei->i_last_alloc_group = ~0;

        ext4_set_inode_flags(inode);
        if (IS_DIRSYNC(inode))
                ext4_handle_sync(handle);
        if (insert_inode_locked(inode) < 0) {
                err = -EINVAL;
                goto fail_drop;
        }
        spin_lock(&sbi->s_next_gen_lock);
        inode->i_generation = sbi->s_next_generation++;
        spin_unlock(&sbi->s_next_gen_lock);

        ei->i_state = EXT4_STATE_NEW;

        ei->i_extra_isize = EXT4_SB(sb)->s_want_extra_isize;

        ret = inode;
        if (vfs_dq_alloc_inode(inode)) {
                err = -EDQUOT;
                goto fail_drop;
        }

        err = ext4_init_acl(handle, inode, dir);
        if (err)
                goto fail_free_drop;

        err = ext4_init_security(handle, inode, dir);
        if (err)
                goto fail_free_drop;

        if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_EXTENTS)) {
                /* set extent flag only for directory, file and normal symlink*/
                if (S_ISDIR(mode) || S_ISREG(mode) || S_ISLNK(mode)) {
                        EXT4_I(inode)->i_flags |= EXT4_EXTENTS_FL;
                        ext4_ext_tree_init(handle, inode);
                }
        }

        err = ext4_mark_inode_dirty(handle, inode);
        if (err) {
                ext4_std_error(sb, err);
                goto fail_free_drop;
        }

        ext4_debug("allocating inode %lu\n", inode->i_ino);
        trace_ext4_allocate_inode(inode, dir, mode);
        goto really_out;
fail:
        ext4_std_error(sb, err);
out:
        iput(inode);
        ret = ERR_PTR(err);
really_out:
        brelse(inode_bitmap_bh);
        return ret;

fail_free_drop:
        vfs_dq_free_inode(inode);

fail_drop:
        vfs_dq_drop(inode);
        inode->i_flags |= S_NOQUOTA;
        inode->i_nlink = 0;
        unlock_new_inode(inode);
        iput(inode);
        brelse(inode_bitmap_bh);
        return ERR_PTR(err);
}

/* Verify that we are loading a valid orphan from disk */
struct inode *ext4_orphan_get(struct super_block *sb, unsigned long ino)
{
        unsigned long max_ino = le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count);
        ext4_group_t block_group;
        int bit;
        struct buffer_head *bitmap_bh;
        struct inode *inode = NULL;
        long err = -EIO;

        /* Error cases - e2fsck has already cleaned up for us */
        if (ino > max_ino) {
                ext4_warning(sb, __func__,
                             "bad orphan ino %lu!  e2fsck was run?", ino);
                goto error;
        }

        block_group = (ino - 1) / EXT4_INODES_PER_GROUP(sb);
        bit = (ino - 1) % EXT4_INODES_PER_GROUP(sb);
        bitmap_bh = ext4_read_inode_bitmap(sb, block_group);
        if (!bitmap_bh) {
                ext4_warning(sb, __func__,
                             "inode bitmap error for orphan %lu", ino);
                goto error;
        }

        /* Having the inode bit set should be a 100% indicator that this
         * is a valid orphan (no e2fsck run on fs).  Orphans also include
         * inodes that were being truncated, so we can't check i_nlink==0.
         */
        if (!ext4_test_bit(bit, bitmap_bh->b_data))
                goto bad_orphan;

        inode = ext4_iget(sb, ino);
        if (IS_ERR(inode))
                goto iget_failed;

        /*
         * If the orphans has i_nlinks > 0 then it should be able to be
         * truncated, otherwise it won't be removed from the orphan list
         * during processing and an infinite loop will result.
         */
        if (inode->i_nlink && !ext4_can_truncate(inode))
                goto bad_orphan;

        if (NEXT_ORPHAN(inode) > max_ino)
                goto bad_orphan;
        brelse(bitmap_bh);
        return inode;

iget_failed:
        err = PTR_ERR(inode);
        inode = NULL;
bad_orphan:
        ext4_warning(sb, __func__,
                     "bad orphan inode %lu!  e2fsck was run?", ino);
        printk(KERN_NOTICE "ext4_test_bit(bit=%d, block=%llu) = %d\n",
               bit, (unsigned long long)bitmap_bh->b_blocknr,
               ext4_test_bit(bit, bitmap_bh->b_data));
        printk(KERN_NOTICE "inode=%p\n", inode);
        if (inode) {
                printk(KERN_NOTICE "is_bad_inode(inode)=%d\n",
                       is_bad_inode(inode));
                printk(KERN_NOTICE "NEXT_ORPHAN(inode)=%u\n",
                       NEXT_ORPHAN(inode));
                printk(KERN_NOTICE "max_ino=%lu\n", max_ino);
                printk(KERN_NOTICE "i_nlink=%u\n", inode->i_nlink);
                /* Avoid freeing blocks if we got a bad deleted inode */
                if (inode->i_nlink == 0)
                        inode->i_blocks = 0;
                iput(inode);
        }
        brelse(bitmap_bh);
error:
        return ERR_PTR(err);
}

unsigned long ext4_count_free_inodes(struct super_block *sb)
{
        unsigned long desc_count;
        struct ext4_group_desc *gdp;
        ext4_group_t i, ngroups = ext4_get_groups_count(sb);
#ifdef EXT4FS_DEBUG
        struct ext4_super_block *es;
        unsigned long bitmap_count, x;
        struct buffer_head *bitmap_bh = NULL;

        es = EXT4_SB(sb)->s_es;
        desc_count = 0;
        bitmap_count = 0;
        gdp = NULL;
        for (i = 0; i < ngroups; i++) {
                gdp = ext4_get_group_desc(sb, i, NULL);
                if (!gdp)
                        continue;
                desc_count += ext4_free_inodes_count(sb, gdp);
                brelse(bitmap_bh);
                bitmap_bh = ext4_read_inode_bitmap(sb, i);
                if (!bitmap_bh)
                        continue;

                x = ext4_count_free(bitmap_bh, EXT4_INODES_PER_GROUP(sb) / 8);
                printk(KERN_DEBUG "group %lu: stored = %d, counted = %lu\n",
                        i, ext4_free_inodes_count(sb, gdp), x);
                bitmap_count += x;
        }
        brelse(bitmap_bh);
        printk(KERN_DEBUG "ext4_count_free_inodes: "
               "stored = %u, computed = %lu, %lu\n",
               le32_to_cpu(es->s_free_inodes_count), desc_count, bitmap_count);
        return desc_count;
#else
        desc_count = 0;
        for (i = 0; i < ngroups; i++) {
                gdp = ext4_get_group_desc(sb, i, NULL);
                if (!gdp)
                        continue;
                desc_count += ext4_free_inodes_count(sb, gdp);
                cond_resched();
        }
        return desc_count;
#endif
}

/* Called at mount-time, super-block is locked */
unsigned long ext4_count_dirs(struct super_block * sb)
{
        unsigned long count = 0;
        ext4_group_t i, ngroups = ext4_get_groups_count(sb);

        for (i = 0; i < ngroups; i++) {
                struct ext4_group_desc *gdp = ext4_get_group_desc(sb, i, NULL);
                if (!gdp)
                        continue;
                count += ext4_used_dirs_count(sb, gdp);
        }
        return count;
}