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From: crosslonelyover on 12 Jul 2010 10:30
Hi,
I walked through ext2_xattr_get, and felt that we can
do some optimization on it. For name_len check, it's done
after down xattr_sem and sb_read, both of which are time
consuming operation compared with strlen:
down_read(&EXT2_I(inode)->xattr_sem);
...
bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);
...
/* find named attribute */
name_len = strlen(name);

error = -ERANGE;
if (name_len > 255)
goto cleanup;

Most of the case, you'll get one valid block, but if the
name len > 255, then the xattr_sem down and sb_bread operation
can be seen as a waste of time. So I think we'd better do
name len check as early as possible.
Following is my patch, and it's against 2.6.35-rc4.
Please check it.

Signed-off-by: Wang Sheng-Hui <crosslonelyover(a)gmail.com>
---
fs/ext2/xattr.c | 12 +++++++-----
1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
index 7c39157..0b94d61 100644
--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -161,6 +161,13 @@ ext2_xattr_get(struct inode *inode, int name_index, const char *name,

if (name == NULL)
return -EINVAL;
+
+ /* find named attribute */
+ name_len = strlen(name);
+ error = -ERANGE;
+ if (name_len > 255)
+ goto cleanup;
+
down_read(&EXT2_I(inode)->xattr_sem);
error = -ENODATA;
if (!EXT2_I(inode)->i_file_acl)
@@ -181,12 +188,7 @@ bad_block: ext2_error(inode->i_sb, "ext2_xattr_get",
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 =
--
1.7.1.1






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Prev: perf: Re-Add make_absolute_path
Next: [PATCH] staging: mrst-touchscreen: fix leaks