[PATCH 36/41] union-mount: Increment read-only users count for read-only layer

[Valerie Aurora]

Union mounts want to guarantee that the read-only layer is read-only -
and stays read-only.  Use the new superblock read-only user count.

XXX - Put common code in loopback and regular mounts in a function

Signed-off-by: Valerie Aurora <vaurora@xxxxxxxxxx>
---
 fs/namespace.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 0280e5b..505974a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1111,6 +1111,11 @@ static int do_umount(struct vfsmount *mnt, int flags)
 	spin_unlock(&vfsmount_lock);
 	if (retval)
 		security_sb_umount_busy(mnt);
+	/* If this was a union mount, we are no longer a read-only
+	 * user on the underlying mount */
+	if (mnt->mnt_flags & MNT_UNION)
+		mnt->mnt_parent->mnt_sb->s_readonly_users--;
+
 	up_write(&namespace_sem);
 	release_mounts(&umount_list);
 	return retval;
@@ -1511,6 +1516,10 @@ static int do_loopback(struct path *path, char *old_name, int recurse,
 		release_mounts(&umount_list);
 	}
 
+	/* If this is a union mount, add ourselves to the readonly users */
+	if (mnt_flags & MNT_UNION)
+		mnt->mnt_parent->mnt_sb->s_readonly_users++;
+
 out:
 	up_write(&namespace_sem);
 	path_put(&old_path);
@@ -1730,6 +1739,10 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path,
 	if ((err = graft_tree(newmnt, path)))
 		goto unlock;
 
+	/* If this is a union mount, add ourselves to the readonly users */
+	if (mnt_flags & MNT_UNION)
+		newmnt->mnt_parent->mnt_sb->s_readonly_users++;
+
 	if (fslist) /* add to the specified expiration list */
 		list_add_tail(&newmnt->mnt_expire, fslist);
 
-- 
1.6.3.3

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