[PATCH 21/27] r-o-bind-mounts-make-access-use-mnt-check

Dave Hansen
2007-11-01T23:15:47Z

It is OK to let access() go without using a mnt_want/drop_write() pair because
it doesn't actually do writes to the filesystem, and it is inherently racy
anyway. This is a rare case when it is OK to use __mnt_is_readonly()
directly.

Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

linux-2.6.git-dave/fs/open.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff -puN fs/open.c~r-o-bind-mounts-make-access-use-mnt-check fs/open.c
--- linux-2.6.git/fs/open.c~r-o-bind-mounts-make-access-use-mnt-check 2007-11-01 14:46:18.000000000 -0700
+++ linux-2.6.git-dave/fs/open.c 2007-11-01 14:46:18.000000000 -0700
@@ -459,8 +459,17 @@ asmlinkage long sys_faccessat(int dfd, c
if(res || !(mode & S_IWOTH) ||
special_file(nd.dentry->d_inode->i_mode))
goto out_path_release;
-
- if(IS_RDONLY(nd.dentry->d_inode))
+ /*
+ * This is a rare case where using __mnt_is_readonly()
+ * is OK without a mnt_want/drop_write() pair. Since
+ * no actual write to the fs is performed here, we do
+ * not need to telegraph to that to anyone.
+ *
+ * By doing this, we accept that this access is
+ * inherently racy and know that the fs may change
+ * state before we even see this result.
+ */
+ if (__mnt_is_readonly(nd.mnt))
res = -EROFS;

out_path_release:
_