xattr.c

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/*
 * linux/fs/ext2/xattr.c
 *
 * Copyright (C) 2001-2003 Andreas Gruenbacher <[email protected]>
 *
 * Fix by Harrison Xing <[email protected]>.
 * Extended attributes for symlinks and special files added per
 *  suggestion of Luka Renko <[email protected]>.
 * xattr consolidation Copyright (c) 2004 James Morris <[email protected]>,
 *  Red Hat Inc.
 *
 */

/*
 * Extended attributes are stored on disk blocks allocated outside of
 * any inode. The i_file_acl field is then made to point to this allocated
 * block. If all extended attributes of an inode are identical, these
 * inodes may share the same extended attribute block. Such situations
 * are automatically detected by keeping a cache of recent attribute block
 * numbers and hashes over the block's contents in memory.
 *
 *
 * Extended attribute block layout:
 *
 *   +------------------+
 *   | header           |
 *   | entry 1          | |
 *   | entry 2          | | growing downwards
 *   | entry 3          | v
 *   | four null bytes  |
 *   | . . .            |
 *   | value 1          | ^
 *   | value 3          | | growing upwards
 *   | value 2          | |
 *   +------------------+
 *
 * The block header is followed by multiple entry descriptors. These entry
 * descriptors are variable in size, and aligned to EXT2_XATTR_PAD
 * byte boundaries. The entry descriptors are sorted by attribute name,
 * so that two extended attribute blocks can be compared efficiently.
 *
 * Attribute values are aligned to the end of the block, stored in
 * no specific order. They are also padded to EXT2_XATTR_PAD byte
 * boundaries. No additional gaps are left between them.
 *
 * Locking strategy
 * ----------------
 * EXT2_I(inode)->i_file_acl is protected by EXT2_I(inode)->xattr_sem.
 * EA blocks are only changed if they are exclusive to an inode, so
 * holding xattr_sem also means that nothing but the EA block's reference
 * count will change. Multiple writers to an EA block are synchronized
 * by the bh lock. No more than a single bh lock is held at any time
 * to avoid deadlocks.
 */

#include <linux/buffer_head.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/mbcache.h>
#include <linux/quotaops.h>
#include <linux/rwsem.h>
#include <linux/security.h>
#include "ext2.h"
#include "xattr.h"
#include "acl.h"

#define HDR(bh) ((struct ext2_xattr_header *)((bh)->b_data))
#define ENTRY(ptr) ((struct ext2_xattr_entry *)(ptr))
#define FIRST_ENTRY(bh) ENTRY(HDR(bh)+1)
#define IS_LAST_ENTRY(entry) (*(__u32 *)(entry) == 0)

#ifdef EXT2_XATTR_DEBUG
# define ea_idebug(inode, f...) do { \
        printk(KERN_DEBUG "inode %s:%ld: ", \
            inode->i_sb->s_id, inode->i_ino); \
        printk(f); \
        printk("\n"); \
    } while (0)
# define ea_bdebug(bh, f...) do { \
        char b[BDEVNAME_SIZE]; \
        printk(KERN_DEBUG "block %s:%lu: ", \
            bdevname(bh->b_bdev, b), \
            (unsigned long) bh->b_blocknr); \
        printk(f); \
        printk("\n"); \
    } while (0)
#else
# define ea_idebug(f...)
# define ea_bdebug(f...)
#endif

static int ext2_xattr_set2(struct inode *, struct buffer_head *,
               struct ext2_xattr_header *);

static int ext2_xattr_cache_insert(struct buffer_head *);
static struct buffer_head *ext2_xattr_cache_find(struct inode *,
                         struct ext2_xattr_header *);
static void ext2_xattr_rehash(struct ext2_xattr_header *,
                  struct ext2_xattr_entry *);

static struct mb_cache *ext2_xattr_cache;

static const struct xattr_handler *ext2_xattr_handler_map[] = {
    [EXT2_XATTR_INDEX_USER]          = &ext2_xattr_user_handler,
#ifdef CONFIG_EXT2_FS_POSIX_ACL
    [EXT2_XATTR_INDEX_POSIX_ACL_ACCESS]  = &ext2_xattr_acl_access_handler,
    [EXT2_XATTR_INDEX_POSIX_ACL_DEFAULT] = &ext2_xattr_acl_default_handler,
#endif
    [EXT2_XATTR_INDEX_TRUSTED]       = &ext2_xattr_trusted_handler,
#ifdef CONFIG_EXT2_FS_SECURITY
    [EXT2_XATTR_INDEX_SECURITY]      = &ext2_xattr_security_handler,
#endif
};

const struct xattr_handler *ext2_xattr_handlers[] = {
    &ext2_xattr_user_handler,
    &ext2_xattr_trusted_handler,
#ifdef CONFIG_EXT2_FS_POSIX_ACL
    &ext2_xattr_acl_access_handler,
    &ext2_xattr_acl_default_handler,
#endif
#ifdef CONFIG_EXT2_FS_SECURITY
    &ext2_xattr_security_handler,
#endif
    NULL
};

static inline const struct xattr_handler *
ext2_xattr_handler(int name_index)
{
    const struct xattr_handler *handler = NULL;

    if (name_index > 0 && name_index < ARRAY_SIZE(ext2_xattr_handler_map))
        handler = ext2_xattr_handler_map[name_index];
    return handler;
}

/*
 * ext2_xattr_get()
 *
 * Copy an extended attribute into the buffer
 * provided, or compute the buffer size required.
 * Buffer is NULL to compute the size of the buffer required.
 *
 * Returns a negative error number on failure, or the number of bytes
 * used / required on success.
 */
int
ext2_xattr_get(struct inode *inode, int name_index, const char *name,
           void *buffer, size_t buffer_size)
{
    struct buffer_head *bh = NULL;
    struct ext2_xattr_entry *entry;
    size_t name_len, size;
    char *end;
    int error;

    ea_idebug(inode, "name=%d.%s, buffer=%p, buffer_size=%ld",
          name_index, name, buffer, (long)buffer_size);

    if (name == NULL)
        return -EINVAL;
    name_len = strlen(name);
    if (name_len > 255)
        return -ERANGE;

    down_read(&EXT2_I(inode)->xattr_sem);
    error = -ENODATA;
    if (!EXT2_I(inode)->i_file_acl)
        goto cleanup;
    ea_idebug(inode, "reading block %d", EXT2_I(inode)->i_file_acl);
    bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);
    error = -EIO;
    if (!bh)
        goto cleanup;
    ea_bdebug(bh, "b_count=%d, refcount=%d",
        atomic_read(&(bh->b_count)), le32_to_cpu(HDR(bh)->h_refcount));
    end = bh->b_data + bh->b_size;
    if (HDR(bh)->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||
        HDR(bh)->h_blocks != cpu_to_le32(1)) {
bad_block:  ext2_error(inode->i_sb, "ext2_xattr_get",
            "inode %ld: bad block %d", inode->i_ino,
            EXT2_I(inode)->i_file_acl);
        error = -EIO;
        goto cleanup;
    }

    /* find named attribute */
    entry = FIRST_ENTRY(bh);
    while (!IS_LAST_ENTRY(entry)) {
        struct ext2_xattr_entry *next =
            EXT2_XATTR_NEXT(entry);
        if ((char *)next >= end)
            goto bad_block;
        if (name_index == entry->e_name_index &&
            name_len == entry->e_name_len &&
            memcmp(name, entry->e_name, name_len) == 0)
            goto found;
        entry = next;
    }
    if (ext2_xattr_cache_insert(bh))
        ea_idebug(inode, "cache insert failed");
    error = -ENODATA;
    goto cleanup;
found:
    /* check the buffer size */
    if (entry->e_value_block != 0)
        goto bad_block;
    size = le32_to_cpu(entry->e_value_size);
    if (size > inode->i_sb->s_blocksize ||
        le16_to_cpu(entry->e_value_offs) + size > inode->i_sb->s_blocksize)
        goto bad_block;

    if (ext2_xattr_cache_insert(bh))
        ea_idebug(inode, "cache insert failed");
    if (buffer) {
        error = -ERANGE;
        if (size > buffer_size)
            goto cleanup;
        /* return value of attribute */
        memcpy(buffer, bh->b_data + le16_to_cpu(entry->e_value_offs),
            size);
    }
    error = size;

cleanup:
    brelse(bh);
    up_read(&EXT2_I(inode)->xattr_sem);

    return error;
}

/*
 * ext2_xattr_list()
 *
 * Copy a list of attribute names into the buffer
 * provided, or compute the buffer size required.
 * Buffer is NULL to compute the size of the buffer required.
 *
 * Returns a negative error number on failure, or the number of bytes
 * used / required on success.
 */
static int
ext2_xattr_list(struct dentry *dentry, char *buffer, size_t buffer_size)
{
    struct inode *inode = dentry->d_inode;
    struct buffer_head *bh = NULL;
    struct ext2_xattr_entry *entry;
    char *end;
    size_t rest = buffer_size;
    int error;

    ea_idebug(inode, "buffer=%p, buffer_size=%ld",
          buffer, (long)buffer_size);

    down_read(&EXT2_I(inode)->xattr_sem);
    error = 0;
    if (!EXT2_I(inode)->i_file_acl)
        goto cleanup;
    ea_idebug(inode, "reading block %d", EXT2_I(inode)->i_file_acl);
    bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);
    error = -EIO;
    if (!bh)
        goto cleanup;
    ea_bdebug(bh, "b_count=%d, refcount=%d",
        atomic_read(&(bh->b_count)), le32_to_cpu(HDR(bh)->h_refcount));
    end = bh->b_data + bh->b_size;
    if (HDR(bh)->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||
        HDR(bh)->h_blocks != cpu_to_le32(1)) {
bad_block:  ext2_error(inode->i_sb, "ext2_xattr_list",
            "inode %ld: bad block %d", inode->i_ino,
            EXT2_I(inode)->i_file_acl);
        error = -EIO;
        goto cleanup;
    }

    /* check the on-disk data structure */
    entry = FIRST_ENTRY(bh);
    while (!IS_LAST_ENTRY(entry)) {
        struct ext2_xattr_entry *next = EXT2_XATTR_NEXT(entry);

        if ((char *)next >= end)
            goto bad_block;
        entry = next;
    }
    if (ext2_xattr_cache_insert(bh))
        ea_idebug(inode, "cache insert failed");

    /* list the attribute names */
    for (entry = FIRST_ENTRY(bh); !IS_LAST_ENTRY(entry);
         entry = EXT2_XATTR_NEXT(entry)) {
        const struct xattr_handler *handler =
            ext2_xattr_handler(entry->e_name_index);

        if (handler) {
            size_t size = handler->list(dentry, buffer, rest,
                            entry->e_name,
                            entry->e_name_len,
                            handler->flags);
            if (buffer) {
                if (size > rest) {
                    error = -ERANGE;
                    goto cleanup;
                }
                buffer += size;
            }
            rest -= size;
        }
    }
    error = buffer_size - rest;  /* total size */

cleanup:
    brelse(bh);
    up_read(&EXT2_I(inode)->xattr_sem);

    return error;
}

/*
 * Inode operation listxattr()
 *
 * dentry->d_inode->i_mutex: don't care
 */
ssize_t
ext2_listxattr(struct dentry *dentry, char *buffer, size_t size)
{
    return ext2_xattr_list(dentry, buffer, size);
}

/*
 * If the EXT2_FEATURE_COMPAT_EXT_ATTR feature of this file system is
 * not set, set it.
 */
static void ext2_xattr_update_super_block(struct super_block *sb)
{
    if (EXT2_HAS_COMPAT_FEATURE(sb, EXT2_FEATURE_COMPAT_EXT_ATTR))
        return;

    spin_lock(&EXT2_SB(sb)->s_lock);
    EXT2_SET_COMPAT_FEATURE(sb, EXT2_FEATURE_COMPAT_EXT_ATTR);
    spin_unlock(&EXT2_SB(sb)->s_lock);
    mark_buffer_dirty(EXT2_SB(sb)->s_sbh);
}

/*
 * ext2_xattr_set()
 *
 * Create, replace or remove an extended attribute for this inode.  Value
 * is NULL to remove an existing extended attribute, and non-NULL to
 * either replace an existing extended attribute, or create a new extended
 * attribute. The flags XATTR_REPLACE and XATTR_CREATE
 * specify that an extended attribute must exist and must not exist
 * previous to the call, respectively.
 *
 * Returns 0, or a negative error number on failure.
 */
int
ext2_xattr_set(struct inode *inode, int name_index, const char *name,
           const void *value, size_t value_len, int flags)
{
    struct super_block *sb = inode->i_sb;
    struct buffer_head *bh = NULL;
    struct ext2_xattr_header *header = NULL;
    struct ext2_xattr_entry *here, *last;
    size_t name_len, free, min_offs = sb->s_blocksize;
    int not_found = 1, error;
    char *end;
    
    /*
     * header -- Points either into bh, or to a temporarily
     *           allocated buffer.
     * here -- The named entry found, or the place for inserting, within
     *         the block pointed to by header.
     * last -- Points right after the last named entry within the block
     *         pointed to by header.
     * min_offs -- The offset of the first value (values are aligned
     *             towards the end of the block).
     * end -- Points right after the block pointed to by header.
     */
    
    ea_idebug(inode, "name=%d.%s, value=%p, value_len=%ld",
          name_index, name, value, (long)value_len);

    if (value == NULL)
        value_len = 0;
    if (name == NULL)
        return -EINVAL;
    name_len = strlen(name);
    if (name_len > 255 || value_len > sb->s_blocksize)
        return -ERANGE;
    down_write(&EXT2_I(inode)->xattr_sem);
    if (EXT2_I(inode)->i_file_acl) {
        /* The inode already has an extended attribute block. */
        bh = sb_bread(sb, EXT2_I(inode)->i_file_acl);
        error = -EIO;
        if (!bh)
            goto cleanup;
        ea_bdebug(bh, "b_count=%d, refcount=%d",
            atomic_read(&(bh->b_count)),
            le32_to_cpu(HDR(bh)->h_refcount));
        header = HDR(bh);
        end = bh->b_data + bh->b_size;
        if (header->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||
            header->h_blocks != cpu_to_le32(1)) {
bad_block:      ext2_error(sb, "ext2_xattr_set",
                "inode %ld: bad block %d", inode->i_ino, 
                   EXT2_I(inode)->i_file_acl);
            error = -EIO;
            goto cleanup;
        }
        /* Find the named attribute. */
        here = FIRST_ENTRY(bh);
        while (!IS_LAST_ENTRY(here)) {
            struct ext2_xattr_entry *next = EXT2_XATTR_NEXT(here);
            if ((char *)next >= end)
                goto bad_block;
            if (!here->e_value_block && here->e_value_size) {
                size_t offs = le16_to_cpu(here->e_value_offs);
                if (offs < min_offs)
                    min_offs = offs;
            }
            not_found = name_index - here->e_name_index;
            if (!not_found)
                not_found = name_len - here->e_name_len;
            if (!not_found)
                not_found = memcmp(name, here->e_name,name_len);
            if (not_found <= 0)
                break;
            here = next;
        }
        last = here;
        /* We still need to compute min_offs and last. */
        while (!IS_LAST_ENTRY(last)) {
            struct ext2_xattr_entry *next = EXT2_XATTR_NEXT(last);
            if ((char *)next >= end)
                goto bad_block;
            if (!last->e_value_block && last->e_value_size) {
                size_t offs = le16_to_cpu(last->e_value_offs);
                if (offs < min_offs)
                    min_offs = offs;
            }
            last = next;
        }

        /* Check whether we have enough space left. */
        free = min_offs - ((char*)last - (char*)header) - sizeof(__u32);
    } else {
        /* We will use a new extended attribute block. */
        free = sb->s_blocksize -
            sizeof(struct ext2_xattr_header) - sizeof(__u32);
        here = last = NULL;  /* avoid gcc uninitialized warning. */
    }

    if (not_found) {
        /* Request to remove a nonexistent attribute? */
        error = -ENODATA;
        if (flags & XATTR_REPLACE)
            goto cleanup;
        error = 0;
        if (value == NULL)
            goto cleanup;
    } else {
        /* Request to create an existing attribute? */
        error = -EEXIST;
        if (flags & XATTR_CREATE)
            goto cleanup;
        if (!here->e_value_block && here->e_value_size) {
            size_t size = le32_to_cpu(here->e_value_size);

            if (le16_to_cpu(here->e_value_offs) + size > 
                sb->s_blocksize || size > sb->s_blocksize)
                goto bad_block;
            free += EXT2_XATTR_SIZE(size);
        }
        free += EXT2_XATTR_LEN(name_len);
    }
    error = -ENOSPC;
    if (free < EXT2_XATTR_LEN(name_len) + EXT2_XATTR_SIZE(value_len))
        goto cleanup;

    /* Here we know that we can set the new attribute. */

    if (header) {
        struct mb_cache_entry *ce;

        /* assert(header == HDR(bh)); */
        ce = mb_cache_entry_get(ext2_xattr_cache, bh->b_bdev,
                    bh->b_blocknr);
        lock_buffer(bh);
        if (header->h_refcount == cpu_to_le32(1)) {
            ea_bdebug(bh, "modifying in-place");
            if (ce)
                mb_cache_entry_free(ce);
            /* keep the buffer locked while modifying it. */
        } else {
            int offset;

            if (ce)
                mb_cache_entry_release(ce);
            unlock_buffer(bh);
            ea_bdebug(bh, "cloning");
            header = kmalloc(bh->b_size, GFP_KERNEL);
            error = -ENOMEM;
            if (header == NULL)
                goto cleanup;
            memcpy(header, HDR(bh), bh->b_size);
            header->h_refcount = cpu_to_le32(1);

            offset = (char *)here - bh->b_data;
            here = ENTRY((char *)header + offset);
            offset = (char *)last - bh->b_data;
            last = ENTRY((char *)header + offset);
        }
    } else {
        /* Allocate a buffer where we construct the new block. */
        header = kzalloc(sb->s_blocksize, GFP_KERNEL);
        error = -ENOMEM;
        if (header == NULL)
            goto cleanup;
        end = (char *)header + sb->s_blocksize;
        header->h_magic = cpu_to_le32(EXT2_XATTR_MAGIC);
        header->h_blocks = header->h_refcount = cpu_to_le32(1);
        last = here = ENTRY(header+1);
    }

    /* Iff we are modifying the block in-place, bh is locked here. */

    if (not_found) {
        /* Insert the new name. */
        size_t size = EXT2_XATTR_LEN(name_len);
        size_t rest = (char *)last - (char *)here;
        memmove((char *)here + size, here, rest);
        memset(here, 0, size);
        here->e_name_index = name_index;
        here->e_name_len = name_len;
        memcpy(here->e_name, name, name_len);
    } else {
        if (!here->e_value_block && here->e_value_size) {
            char *first_val = (char *)header + min_offs;
            size_t offs = le16_to_cpu(here->e_value_offs);
            char *val = (char *)header + offs;
            size_t size = EXT2_XATTR_SIZE(
                le32_to_cpu(here->e_value_size));

            if (size == EXT2_XATTR_SIZE(value_len)) {
                /* The old and the new value have the same
                   size. Just replace. */
                here->e_value_size = cpu_to_le32(value_len);
                memset(val + size - EXT2_XATTR_PAD, 0,
                       EXT2_XATTR_PAD); /* Clear pad bytes. */
                memcpy(val, value, value_len);
                goto skip_replace;
            }

            /* Remove the old value. */
            memmove(first_val + size, first_val, val - first_val);
            memset(first_val, 0, size);
            here->e_value_offs = 0;
            min_offs += size;

            /* Adjust all value offsets. */
            last = ENTRY(header+1);
            while (!IS_LAST_ENTRY(last)) {
                size_t o = le16_to_cpu(last->e_value_offs);
                if (!last->e_value_block && o < offs)
                    last->e_value_offs =
                        cpu_to_le16(o + size);
                last = EXT2_XATTR_NEXT(last);
            }
        }
        if (value == NULL) {
            /* Remove the old name. */
            size_t size = EXT2_XATTR_LEN(name_len);
            last = ENTRY((char *)last - size);
            memmove(here, (char*)here + size,
                (char*)last - (char*)here);
            memset(last, 0, size);
        }
    }

    if (value != NULL) {
        /* Insert the new value. */
        here->e_value_size = cpu_to_le32(value_len);
        if (value_len) {
            size_t size = EXT2_XATTR_SIZE(value_len);
            char *val = (char *)header + min_offs - size;
            here->e_value_offs =
                cpu_to_le16((char *)val - (char *)header);
            memset(val + size - EXT2_XATTR_PAD, 0,
                   EXT2_XATTR_PAD); /* Clear the pad bytes. */
            memcpy(val, value, value_len);
        }
    }

skip_replace:
    if (IS_LAST_ENTRY(ENTRY(header+1))) {
        /* This block is now empty. */
        if (bh && header == HDR(bh))
            unlock_buffer(bh);  /* we were modifying in-place. */
        error = ext2_xattr_set2(inode, bh, NULL);
    } else {
        ext2_xattr_rehash(header, here);
        if (bh && header == HDR(bh))
            unlock_buffer(bh);  /* we were modifying in-place. */
        error = ext2_xattr_set2(inode, bh, header);
    }

cleanup:
    brelse(bh);
    if (!(bh && header == HDR(bh)))
        kfree(header);
    up_write(&EXT2_I(inode)->xattr_sem);

    return error;
}

/*
 * Second half of ext2_xattr_set(): Update the file system.
 */
static int
ext2_xattr_set2(struct inode *inode, struct buffer_head *old_bh,
        struct ext2_xattr_header *header)
{
    struct super_block *sb = inode->i_sb;
    struct buffer_head *new_bh = NULL;
    int error;

    if (header) {
        new_bh = ext2_xattr_cache_find(inode, header);
        if (new_bh) {
            /* We found an identical block in the cache. */
            if (new_bh == old_bh) {
                ea_bdebug(new_bh, "keeping this block");
            } else {
                /* The old block is released after updating
                   the inode.  */
                ea_bdebug(new_bh, "reusing block");

                error = dquot_alloc_block(inode, 1);
                if (error) {
                    unlock_buffer(new_bh);
                    goto cleanup;
                }
                le32_add_cpu(&HDR(new_bh)->h_refcount, 1);
                ea_bdebug(new_bh, "refcount now=%d",
                    le32_to_cpu(HDR(new_bh)->h_refcount));
            }
            unlock_buffer(new_bh);
        } else if (old_bh && header == HDR(old_bh)) {
            /* Keep this block. No need to lock the block as we
               don't need to change the reference count. */
            new_bh = old_bh;
            get_bh(new_bh);
            ext2_xattr_cache_insert(new_bh);
        } else {
            /* We need to allocate a new block */
            ext2_fsblk_t goal = ext2_group_first_block_no(sb,
                        EXT2_I(inode)->i_block_group);
            int block = ext2_new_block(inode, goal, &error);
            if (error)
                goto cleanup;
            ea_idebug(inode, "creating block %d", block);

            new_bh = sb_getblk(sb, block);
            if (!new_bh) {
                ext2_free_blocks(inode, block, 1);
                mark_inode_dirty(inode);
                error = -EIO;
                goto cleanup;
            }
            lock_buffer(new_bh);
            memcpy(new_bh->b_data, header, new_bh->b_size);
            set_buffer_uptodate(new_bh);
            unlock_buffer(new_bh);
            ext2_xattr_cache_insert(new_bh);
            
            ext2_xattr_update_super_block(sb);
        }
        mark_buffer_dirty(new_bh);
        if (IS_SYNC(inode)) {
            sync_dirty_buffer(new_bh);
            error = -EIO;
            if (buffer_req(new_bh) && !buffer_uptodate(new_bh))
                goto cleanup;
        }
    }

    /* Update the inode. */
    EXT2_I(inode)->i_file_acl = new_bh ? new_bh->b_blocknr : 0;
    inode->i_ctime = CURRENT_TIME_SEC;
    if (IS_SYNC(inode)) {
        error = sync_inode_metadata(inode, 1);
        /* In case sync failed due to ENOSPC the inode was actually
         * written (only some dirty data were not) so we just proceed
         * as if nothing happened and cleanup the unused block */
        if (error && error != -ENOSPC) {
            if (new_bh && new_bh != old_bh) {
                dquot_free_block_nodirty(inode, 1);
                mark_inode_dirty(inode);
            }
            goto cleanup;
        }
    } else
        mark_inode_dirty(inode);

    error = 0;
    if (old_bh && old_bh != new_bh) {
        struct mb_cache_entry *ce;

        /*
         * If there was an old block and we are no longer using it,
         * release the old block.
         */
        ce = mb_cache_entry_get(ext2_xattr_cache, old_bh->b_bdev,
                    old_bh->b_blocknr);
        lock_buffer(old_bh);
        if (HDR(old_bh)->h_refcount == cpu_to_le32(1)) {
            /* Free the old block. */
            if (ce)
                mb_cache_entry_free(ce);
            ea_bdebug(old_bh, "freeing");
            ext2_free_blocks(inode, old_bh->b_blocknr, 1);
            mark_inode_dirty(inode);
            /* We let our caller release old_bh, so we
             * need to duplicate the buffer before. */
            get_bh(old_bh);
            bforget(old_bh);
        } else {
            /* Decrement the refcount only. */
            le32_add_cpu(&HDR(old_bh)->h_refcount, -1);
            if (ce)
                mb_cache_entry_release(ce);
            dquot_free_block_nodirty(inode, 1);
            mark_inode_dirty(inode);
            mark_buffer_dirty(old_bh);
            ea_bdebug(old_bh, "refcount now=%d",
                le32_to_cpu(HDR(old_bh)->h_refcount));
        }
        unlock_buffer(old_bh);
    }

cleanup:
    brelse(new_bh);

    return error;
}

/*
 * ext2_xattr_delete_inode()
 *
 * Free extended attribute resources associated with this inode. This
 * is called immediately before an inode is freed.
 */
void
ext2_xattr_delete_inode(struct inode *inode)
{
    struct buffer_head *bh = NULL;
    struct mb_cache_entry *ce;

    down_write(&EXT2_I(inode)->xattr_sem);
    if (!EXT2_I(inode)->i_file_acl)
        goto cleanup;
    bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);
    if (!bh) {
        ext2_error(inode->i_sb, "ext2_xattr_delete_inode",
            "inode %ld: block %d read error", inode->i_ino,
            EXT2_I(inode)->i_file_acl);
        goto cleanup;
    }
    ea_bdebug(bh, "b_count=%d", atomic_read(&(bh->b_count)));
    if (HDR(bh)->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||
        HDR(bh)->h_blocks != cpu_to_le32(1)) {
        ext2_error(inode->i_sb, "ext2_xattr_delete_inode",
            "inode %ld: bad block %d", inode->i_ino,
            EXT2_I(inode)->i_file_acl);
        goto cleanup;
    }
    ce = mb_cache_entry_get(ext2_xattr_cache, bh->b_bdev, bh->b_blocknr);
    lock_buffer(bh);
    if (HDR(bh)->h_refcount == cpu_to_le32(1)) {
        if (ce)
            mb_cache_entry_free(ce);
        ext2_free_blocks(inode, EXT2_I(inode)->i_file_acl, 1);
        get_bh(bh);
        bforget(bh);
        unlock_buffer(bh);
    } else {
        le32_add_cpu(&HDR(bh)->h_refcount, -1);
        if (ce)
            mb_cache_entry_release(ce);
        ea_bdebug(bh, "refcount now=%d",
            le32_to_cpu(HDR(bh)->h_refcount));
        unlock_buffer(bh);
        mark_buffer_dirty(bh);
        if (IS_SYNC(inode))
            sync_dirty_buffer(bh);
        dquot_free_block_nodirty(inode, 1);
    }
    EXT2_I(inode)->i_file_acl = 0;

cleanup:
    brelse(bh);
    up_write(&EXT2_I(inode)->xattr_sem);
}

/*
 * ext2_xattr_put_super()
 *
 * This is called when a file system is unmounted.
 */
void
ext2_xattr_put_super(struct super_block *sb)
{
    mb_cache_shrink(sb->s_bdev);
}


/*
 * ext2_xattr_cache_insert()
 *
 * Create a new entry in the extended attribute cache, and insert
 * it unless such an entry is already in the cache.
 *
 * Returns 0, or a negative error number on failure.
 */
static int
ext2_xattr_cache_insert(struct buffer_head *bh)
{
    __u32 hash = le32_to_cpu(HDR(bh)->h_hash);
    struct mb_cache_entry *ce;
    int error;

    ce = mb_cache_entry_alloc(ext2_xattr_cache, GFP_NOFS);
    if (!ce)
        return -ENOMEM;
    error = mb_cache_entry_insert(ce, bh->b_bdev, bh->b_blocknr, hash);
    if (error) {
        mb_cache_entry_free(ce);
        if (error == -EBUSY) {
            ea_bdebug(bh, "already in cache (%d cache entries)",
                atomic_read(&ext2_xattr_cache->c_entry_count));
            error = 0;
        }
    } else {
        ea_bdebug(bh, "inserting [%x] (%d cache entries)", (int)hash,
              atomic_read(&ext2_xattr_cache->c_entry_count));
        mb_cache_entry_release(ce);
    }
    return error;
}

/*
 * ext2_xattr_cmp()
 *
 * Compare two extended attribute blocks for equality.
 *
 * Returns 0 if the blocks are equal, 1 if they differ, and
 * a negative error number on errors.
 */
static int
ext2_xattr_cmp(struct ext2_xattr_header *header1,
           struct ext2_xattr_header *header2)
{
    struct ext2_xattr_entry *entry1, *entry2;

    entry1 = ENTRY(header1+1);
    entry2 = ENTRY(header2+1);
    while (!IS_LAST_ENTRY(entry1)) {
        if (IS_LAST_ENTRY(entry2))
            return 1;
        if (entry1->e_hash != entry2->e_hash ||
            entry1->e_name_index != entry2->e_name_index ||
            entry1->e_name_len != entry2->e_name_len ||
            entry1->e_value_size != entry2->e_value_size ||
            memcmp(entry1->e_name, entry2->e_name, entry1->e_name_len))
            return 1;
        if (entry1->e_value_block != 0 || entry2->e_value_block != 0)
            return -EIO;
        if (memcmp((char *)header1 + le16_to_cpu(entry1->e_value_offs),
               (char *)header2 + le16_to_cpu(entry2->e_value_offs),
               le32_to_cpu(entry1->e_value_size)))
            return 1;

        entry1 = EXT2_XATTR_NEXT(entry1);
        entry2 = EXT2_XATTR_NEXT(entry2);
    }
    if (!IS_LAST_ENTRY(entry2))
        return 1;
    return 0;
}

/*
 * ext2_xattr_cache_find()
 *
 * Find an identical extended attribute block.
 *
 * Returns a locked buffer head to the block found, or NULL if such
 * a block was not found or an error occurred.
 */
static struct buffer_head *
ext2_xattr_cache_find(struct inode *inode, struct ext2_xattr_header *header)
{
    __u32 hash = le32_to_cpu(header->h_hash);
    struct mb_cache_entry *ce;

    if (!header->h_hash)
        return NULL;  /* never share */
    ea_idebug(inode, "looking for cached blocks [%x]", (int)hash);
again:
    ce = mb_cache_entry_find_first(ext2_xattr_cache, inode->i_sb->s_bdev,
                       hash);
    while (ce) {
        struct buffer_head *bh;

        if (IS_ERR(ce)) {
            if (PTR_ERR(ce) == -EAGAIN)
                goto again;
            break;
        }

        bh = sb_bread(inode->i_sb, ce->e_block);
        if (!bh) {
            ext2_error(inode->i_sb, "ext2_xattr_cache_find",
                "inode %ld: block %ld read error",
                inode->i_ino, (unsigned long) ce->e_block);
        } else {
            lock_buffer(bh);
            if (le32_to_cpu(HDR(bh)->h_refcount) >
                   EXT2_XATTR_REFCOUNT_MAX) {
                ea_idebug(inode, "block %ld refcount %d>%d",
                      (unsigned long) ce->e_block,
                      le32_to_cpu(HDR(bh)->h_refcount),
                      EXT2_XATTR_REFCOUNT_MAX);
            } else if (!ext2_xattr_cmp(header, HDR(bh))) {
                ea_bdebug(bh, "b_count=%d",
                      atomic_read(&(bh->b_count)));
                mb_cache_entry_release(ce);
                return bh;
            }
            unlock_buffer(bh);
            brelse(bh);
        }
        ce = mb_cache_entry_find_next(ce, inode->i_sb->s_bdev, hash);
    }
    return NULL;
}

#define NAME_HASH_SHIFT 5
#define VALUE_HASH_SHIFT 16

/*
 * ext2_xattr_hash_entry()
 *
 * Compute the hash of an extended attribute.
 */
static inline void ext2_xattr_hash_entry(struct ext2_xattr_header *header,
                     struct ext2_xattr_entry *entry)
{
    __u32 hash = 0;
    char *name = entry->e_name;
    int n;

    for (n=0; n < entry->e_name_len; n++) {
        hash = (hash << NAME_HASH_SHIFT) ^
               (hash >> (8*sizeof(hash) - NAME_HASH_SHIFT)) ^
               *name++;
    }

    if (entry->e_value_block == 0 && entry->e_value_size != 0) {
        __le32 *value = (__le32 *)((char *)header +
            le16_to_cpu(entry->e_value_offs));
        for (n = (le32_to_cpu(entry->e_value_size) +
             EXT2_XATTR_ROUND) >> EXT2_XATTR_PAD_BITS; n; n--) {
            hash = (hash << VALUE_HASH_SHIFT) ^
                   (hash >> (8*sizeof(hash) - VALUE_HASH_SHIFT)) ^
                   le32_to_cpu(*value++);
        }
    }
    entry->e_hash = cpu_to_le32(hash);
}

#undef NAME_HASH_SHIFT
#undef VALUE_HASH_SHIFT

#define BLOCK_HASH_SHIFT 16

/*
 * ext2_xattr_rehash()
 *
 * Re-compute the extended attribute hash value after an entry has changed.
 */
static void ext2_xattr_rehash(struct ext2_xattr_header *header,
                  struct ext2_xattr_entry *entry)
{
    struct ext2_xattr_entry *here;
    __u32 hash = 0;
    
    ext2_xattr_hash_entry(header, entry);
    here = ENTRY(header+1);
    while (!IS_LAST_ENTRY(here)) {
        if (!here->e_hash) {
            /* Block is not shared if an entry's hash value == 0 */
            hash = 0;
            break;
        }
        hash = (hash << BLOCK_HASH_SHIFT) ^
               (hash >> (8*sizeof(hash) - BLOCK_HASH_SHIFT)) ^
               le32_to_cpu(here->e_hash);
        here = EXT2_XATTR_NEXT(here);
    }
    header->h_hash = cpu_to_le32(hash);
}

#undef BLOCK_HASH_SHIFT

int __init
init_ext2_xattr(void)
{
    ext2_xattr_cache = mb_cache_create("ext2_xattr", 6);
    if (!ext2_xattr_cache)
        return -ENOMEM;
    return 0;
}

void
exit_ext2_xattr(void)
{
    mb_cache_destroy(ext2_xattr_cache);
}