r8169: spinlock redux.

[linux-2.6.git] / fs / ext2 / xattr.c

/*
 * linux/fs/ext2/xattr.c
 *
 * Copyright (C) 2001-2003 Andreas Gruenbacher <agruen@suse.de>
 *
 * Fix by Harrison Xing <harrison@mountainviewdata.com>.
 * Extended attributes for symlinks and special files added per
 *  suggestion of Luka Renko <luka.renko@hermes.si>.
 * xattr consolidation Copyright (c) 2004 James Morris <jmorris@redhat.com>,
 *  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);
        sb->s_dirt = 1;
        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);
}