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| author | Tahsin Erdogan <tahsin@google.com> | 2017-06-22 11:48:53 -0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2017-06-22 11:48:53 -0400 |
| commit | 9c6e7853c531c7cecca8c257bde767d089e5c880 (patch) | |
| tree | 1d214d0d7da251f2063721240b99c2bfaa3a4afb /fs/ext4 | |
| parent | 7a9ca53aea10ad4677a0f347ad7639c304b80194 (diff) | |
| download | linux-9c6e7853c531c7cecca8c257bde767d089e5c880.tar.bz2 | |
ext4: reserve space for xattr entries/names
New ea_inode feature allows putting large xattr values into external
inodes. struct ext4_xattr_entry and the attribute name however have to
remain in the inode extra space or external attribute block. Once that
space is exhausted, no further entries can be added. Some of that space
could also be used by values that fit in there at the time of addition.
So, a single xattr entry whose value barely fits in the external block
could prevent further entries being added.
To mitigate the problem, this patch introduces a notion of reserved
space in the external attribute block that cannot be used by value data.
This reserve is enforced when ea_inode feature is enabled. The amount
of reserve is arbitrarily chosen to be min(block_size/8, 1024). The
table below shows how much space is reserved for each block size and the
guaranteed mininum number of entries that can be placed in the external
attribute block.
block size reserved bytes entries (name length = 16)
1k 128 3
2k 256 7
4k 512 15
8k 1024 31
16k 1024 31
32k 1024 31
64k 1024 31
Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'fs/ext4')
| -rw-r--r-- | fs/ext4/xattr.c | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 22bfb6221a2d..174d4e4a295f 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -1459,6 +1459,12 @@ static int ext4_xattr_inode_lookup_create(handle_t *handle, struct inode *inode, return 0; } +/* + * Reserve min(block_size/8, 1024) bytes for xattr entries/names if ea_inode + * feature is enabled. + */ +#define EXT4_XATTR_BLOCK_RESERVE(inode) min(i_blocksize(inode)/8, 1024U) + static int ext4_xattr_set_entry(struct ext4_xattr_info *i, struct ext4_xattr_search *s, handle_t *handle, struct inode *inode) @@ -1518,6 +1524,20 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i, ret = -ENOSPC; goto out; } + + /* + * If storing the value in an external inode is an option, + * reserve space for xattr entries/names in the external + * attribute block so that a long value does not occupy the + * whole space and prevent futher entries being added. + */ + if (ext4_has_feature_ea_inode(inode->i_sb) && new_size && + (s->end - s->base) == i_blocksize(inode) && + (min_offs + old_size - new_size) < + EXT4_XATTR_BLOCK_RESERVE(inode)) { + ret = -ENOSPC; + goto out; + } } /* |