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ext4: shortcut setting of xattr to the same value 

When someone tried to set xattr to the same value (i.e., not changing
anything) we did all the work of removing original xattr, possibly
breaking references to shared xattr block, inserting new xattr, and
merging xattr blocks again. Since this is not so rare operation and it
is relatively cheap for us to detect this case, check for this and
shortcut xattr setting in that case.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2016-02-22 22:43:04 -05:00 committed by Theodore Ts'o
parent dc8d5e565f
commit 3fd164629d
1 changed files with 18 additions and 0 deletions
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18
fs/ext4/xattr.c
View File

@ -1096,6 +1096,17 @@ static int ext4_xattr_ibody_set(handle_t *handle, struct inode *inode,
return 0;
}
static int ext4_xattr_value_same(struct ext4_xattr_search *s,
struct ext4_xattr_info *i)
{
void *value;
if (le32_to_cpu(s->here->e_value_size) != i->value_len)
return 0;
value = ((void *)s->base) + le16_to_cpu(s->here->e_value_offs);
return !memcmp(value, i->value, i->value_len);
}
/*
* ext4_xattr_set_handle()
*
@ -1172,6 +1183,13 @@ ext4_xattr_set_handle(handle_t *handle, struct inode *inode, int name_index,
else if (!bs.s.not_found)
error = ext4_xattr_block_set(handle, inode, &i, &bs);
} else {
error = 0;
/* Xattr value did not change? Save us some work and bail out */
if (!is.s.not_found && ext4_xattr_value_same(&is.s, &i))
goto cleanup;
if (!bs.s.not_found && ext4_xattr_value_same(&bs.s, &i))
goto cleanup;
error = ext4_xattr_ibody_set(handle, inode, &i, &is);
if (!error && !bs.s.not_found) {
i.value = NULL;