xattr.c

linux 内核源代码

		/* 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);
}