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, 4 insertions, 20 deletions

diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index f3fbb1bf3f18..f32b8603dca8 100644
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -149,26 +149,10 @@ struct vfsmount *nfs_d_automount(struct path *path)
 	if (IS_ERR(mnt))
 		goto out;
 
-	mntget(mnt);
-	err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE,
-			   &nfs_automount_list);
-	switch (err) {
-	case 0:
-		dprintk("%s: done, success\n", __func__);
-		schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
-		break;
-	case -EBUSY:
-		/* someone else made a mount here whilst we were busy */
-		mntput(mnt);
-		dprintk("%s: done, collision\n", __func__);
-		mnt = NULL;
-		break;
-	default:
-		mntput(mnt);
-		dprintk("%s: done, error %d\n", __func__, err);
-		mnt = ERR_PTR(err);
-		break;
-	}
+	dprintk("%s: done, success\n", __func__);
+	mntget(mnt); /* prevent immediate expiration */
+	mnt_set_expiry(mnt, &nfs_automount_list);
+	schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
 
 out:
 	nfs_free_fattr(fattr);