[Linux-cachefs] [PATCH v2 2/2] cachefiles: extend ro check to private mount
Christian Brauner
brauner at kernel.org
Wed Apr 7 09:02:08 UTC 2021
From: Christian Brauner <christian.brauner at ubuntu.com>
So far cachefiles only verified that the superblock wasn't read-only but
didn't check whether the mount was. This made sense when we did not use
a private mount because the read-only state could change at any point.
Now that we have a private mount and mount properties can't change
behind our back extend the read-only check to include the vfsmount.
The __mnt_is_readonly() helper will check both the mount and the
superblock. Note that before we checked root->d_sb and now we check
mnt->mnt_sb but since we have a matching <vfsmount, dentry> pair here
this is only syntactical change, not a semantic one.
Here's how this works:
mount -o ro --bind /var/cache/fscache/ /var/cache/fscache/
systemctl start cachefilesd
Job for cachefilesd.service failed because the control process exited with error code.
See "systemctl status cachefilesd.service" and "journalctl -xe" for details.
dmesg | grep CacheFiles
[ 2.922514] CacheFiles: Loaded
[ 272.206907] CacheFiles: Failed to register: -30
errno 30
EROFS 30 Read-only file system
Cc: David Howells <dhowells at redhat.com>
Cc: linux-cachefs at redhat.com
Cc: linux-fsdevel at vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
---
/* v2 */
patch introduced
---
fs/cachefiles/bind.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/cachefiles/bind.c b/fs/cachefiles/bind.c
index bbace3e51f52..cb8dd9ecc090 100644
--- a/fs/cachefiles/bind.c
+++ b/fs/cachefiles/bind.c
@@ -141,8 +141,13 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache)
!root->d_sb->s_op->sync_fs)
goto error_unsupported;
+ /*
+ * Verify our mount and superblock aren't read-only.
+ * Note, while our private mount is guaranteed to not change anymore
+ * the superblock may still go read-only later.
+ */
ret = -EROFS;
- if (sb_rdonly(root->d_sb))
+ if (__mnt_is_readonly(cache->mnt))
goto error_unsupported;
/* determine the security of the on-disk cache as this governs
--
2.27.0
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