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authorSargun Dhillon <sargun@sargun.me>2021-01-08 03:10:43 +0300
committerMiklos Szeredi <mszeredi@redhat.com>2021-01-28 12:22:48 +0300
commit335d3fc57941e5c6164c69d439aec1cb7a800876 (patch)
tree452b20f538e376068535fcd6b2f125abec52aaf8 /fs/overlayfs/util.c
parent03fedf93593c82538b18476d8c4f0e8f8435ea70 (diff)
downloadlinux-335d3fc57941e5c6164c69d439aec1cb7a800876.tar.xz
ovl: implement volatile-specific fsync error behaviour
Overlayfs's volatile option allows the user to bypass all forced sync calls to the upperdir filesystem. This comes at the cost of safety. We can never ensure that the user's data is intact, but we can make a best effort to expose whether or not the data is likely to be in a bad state. The best way to handle this in the time being is that if an overlayfs's upperdir experiences an error after a volatile mount occurs, that error will be returned on fsync, fdatasync, sync, and syncfs. This is contradictory to the traditional behaviour of VFS which fails the call once, and only raises an error if a subsequent fsync error has occurred, and been raised by the filesystem. One awkward aspect of the patch is that we have to manually set the superblock's errseq_t after the sync_fs callback as opposed to just returning an error from syncfs. This is because the call chain looks something like this: sys_syncfs -> sync_filesystem -> __sync_filesystem -> /* The return value is ignored here sb->s_op->sync_fs(sb) _sync_blockdev /* Where the VFS fetches the error to raise to userspace */ errseq_check_and_advance Because of this we call errseq_set every time the sync_fs callback occurs. Due to the nature of this seen / unseen dichotomy, if the upperdir is an inconsistent state at the initial mount time, overlayfs will refuse to mount, as overlayfs cannot get a snapshot of the upperdir's errseq that will increment on error until the user calls syncfs. Signed-off-by: Sargun Dhillon <sargun@sargun.me> Suggested-by: Amir Goldstein <amir73il@gmail.com> Reviewed-by: Amir Goldstein <amir73il@gmail.com> Fixes: c86243b090bc ("ovl: provide a mount option "volatile"") Cc: stable@vger.kernel.org Reviewed-by: Vivek Goyal <vgoyal@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs/util.c')
-rw-r--r--fs/overlayfs/util.c27
1 files changed, 27 insertions, 0 deletions
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 6569031af3cd..9826b003f1d2 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -962,3 +962,30 @@ err_free:
kfree(buf);
return ERR_PTR(res);
}
+
+/*
+ * ovl_sync_status() - Check fs sync status for volatile mounts
+ *
+ * Returns 1 if this is not a volatile mount and a real sync is required.
+ *
+ * Returns 0 if syncing can be skipped because mount is volatile, and no errors
+ * have occurred on the upperdir since the mount.
+ *
+ * Returns -errno if it is a volatile mount, and the error that occurred since
+ * the last mount. If the error code changes, it'll return the latest error
+ * code.
+ */
+
+int ovl_sync_status(struct ovl_fs *ofs)
+{
+ struct vfsmount *mnt;
+
+ if (ovl_should_sync(ofs))
+ return 1;
+
+ mnt = ovl_upper_mnt(ofs);
+ if (!mnt)
+ return 0;
+
+ return errseq_check(&mnt->mnt_sb->s_wb_err, ofs->errseq);
+}