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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 alligned 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/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/mbcache.h>
#include <linux/quotaops.h>
#include <linux/rwsem.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 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
};

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 struct xattr_handler *
ext2_xattr_handler(int name_index)
{
      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;
      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 */
      name_len = strlen(name);

      error = -ERANGE;
      if (name_len > 255)
            goto cleanup;
      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;
      }
      /* Check the remaining name entries */
      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");
      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 inode *inode, char *buffer, size_t buffer_size)
{
      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)) {
            struct xattr_handler *handler =
                  ext2_xattr_handler(entry->e_name_index);

            if (handler) {
                  size_t size = handler->list(inode, buffer, rest,
                                        entry->e_name,
                                        entry->e_name_len);
                  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->d_inode, 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;

      EXT2_SET_COMPAT_FEATURE(sb, EXT2_FEATURE_COMPAT_EXT_ATTR);
      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. Buffer
 * 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 = -EDQUOT;
                        if (DQUOT_ALLOC_BLOCK(inode, 1)) {
                              unlock_buffer(new_bh);
                              goto cleanup;
                        }
                        HDR(new_bh)->h_refcount = cpu_to_le32(1 +
                              le32_to_cpu(HDR(new_bh)->h_refcount));
                        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 */
                  int goal = le32_to_cpu(EXT2_SB(sb)->s_es->
                                               s_first_data_block) +
                           EXT2_I(inode)->i_block_group *
                           EXT2_BLOCKS_PER_GROUP(sb);
                  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);
                        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 = ext2_sync_inode (inode);
            /* 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(inode, 1);
                  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);
                  /* 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. */
                  HDR(old_bh)->h_refcount = cpu_to_le32(
                        le32_to_cpu(HDR(old_bh)->h_refcount) - 1);
                  if (ce)
                        mb_cache_entry_release(ce);
                  DQUOT_FREE_BLOCK(inode, 1);
                  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 {
            HDR(bh)->h_refcount = cpu_to_le32(
                  le32_to_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(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);
      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, 0,
                               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, 0, 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", NULL,
            sizeof(struct mb_cache_entry) +
            sizeof(((struct mb_cache_entry *) 0)->e_indexes[0]), 1, 6);
      if (!ext2_xattr_cache)
            return -ENOMEM;
      return 0;
}

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

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