Unexport do_add_mount() and add in follow_automount(), not ->d_automount()

Unexport do_add_mount() and make ->d_automount() return the vfsmount to be
added rather than calling do_add_mount() itself.  follow_automount() will then
do the addition.

This slightly complicates things as ->d_automount() normally wants to add the
new vfsmount to an expiration list and start an expiration timer.  The problem
with that is that the vfsmount will be deleted if it has a refcount of 1 and
the timer will not repeat if the expiration list is empty.

To this end, we require the vfsmount to be returned from d_automount() with a
refcount of (at least) 2.  One of these refs will be dropped unconditionally.
In addition, follow_automount() must get a 3rd ref around the call to
do_add_mount() lest it eat a ref and return an error, leaving the mount we
have open to being expired as we would otherwise have only 1 ref on it.

d_automount() should also add the the vfsmount to the expiration list (by
calling mnt_set_expiry()) and start the expiration timer before returning, if
this mechanism is to be used.  The vfsmount will be unlinked from the
expiration list by follow_automount() if do_add_mount() fails.

This patch also fixes the call to do_add_mount() for AFS to propagate the mount
flags from the parent vfsmount.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 6 insertions, 20 deletions

diff --git a/fs/cifs/cifs_dfs_ref.c b/fs/cifs/cifs_dfs_ref.c
index 0fc1638..7ed3653 100644
--- a/fs/cifs/cifs_dfs_ref.c
+++ b/fs/cifs/cifs_dfs_ref.c
@@ -351,7 +351,6 @@ free_xid:
 struct vfsmount *cifs_dfs_d_automount(struct path *path)
 {
 	struct vfsmount *newmnt;
-	int err;
 
 	cFYI(1, "in %s", __func__);
 
@@ -361,25 +360,12 @@ struct vfsmount *cifs_dfs_d_automount(struct path *path)
 		return newmnt;
 	}
 
-	mntget(newmnt);
-	err = do_add_mount(newmnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE,
-			   &cifs_dfs_automount_list);
-	switch (err) {
-	case 0:
-		schedule_delayed_work(&cifs_dfs_automount_task,
-				      cifs_dfs_mountpoint_expiry_timeout);
-		cFYI(1, "leaving %s [ok]" , __func__);
-		return newmnt;
-	case -EBUSY:
-		/* someone else made a mount here whilst we were busy */
-		mntput(newmnt);
-		cFYI(1, "leaving %s [EBUSY]" , __func__);
-		return NULL;
-	default:
-		mntput(newmnt);
-		cFYI(1, "leaving %s [error %d]" , __func__, err);
-		return ERR_PTR(err);
-	}
+	mntget(newmnt); /* prevent immediate expiration */
+	mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
+	schedule_delayed_work(&cifs_dfs_automount_task,
+			      cifs_dfs_mountpoint_expiry_timeout);
+	cFYI(1, "leaving %s [ok]" , __func__);
+	return newmnt;
 }
 
 const struct inode_operations cifs_dfs_referral_inode_operations = {