On Mon, 14 Dec 2009 10:24:18 -0500 "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote: > On Mon, Dec 14, 2009 at 08:38:43AM -0500, Jeff Layton wrote: > > On Sun, 13 Dec 2009 17:33:15 -0500 > > Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> wrote: > > > > > On Sun, 2009-12-13 at 16:39 -0500, J. Bruce Fields wrote: > > > > On a recent kernel: > > > > > > > > # mount -tnfs4 pearlet1:/ /mnt/ > > > > # find /mnt/ > > > > /mnt/ > > > > find: File system loop detected; `/mnt/DIR' is part of the same > > > > file system loop as `/mnt/'. > > > > > > > > Here /mnt/DIR is a server-side mountpoint, hence has a different fsid > > > > than /mnt/. Wireshark confirms that the server is returning a different > > > > fsid. However, 'strace -v find /mnt/' shows stat returning > > > > st_dev=makedev(0, 22) for both /mnt and /mnt/DIR. > > > > > > > > If I then do a 'ls /mnt/DIR', followed by another find, the error goes > > > > away, and this time an strace shows that stat is returning (0, 23) for > > > > /mnt/DIR. > > > > > > > > I don't see any obvious problem with the network trace, so it looks to > > > > me like the client is failing to recognize the mountpoint when it > > > > should? > > > > > > This is a known consequence of the way we treat submounts (and > > > referrals); we're basically treating them as a special kind of symlink. > > > The problem then arises when syscalls such as stat() fail to set the > > > LOOKUP_FOLLOW flag, and so the user is granted a temporary peek of the > > > underlying inode. > > > > > > I'm not sure how we should treat this. I suppose we could change the > > > test in __link_path_walk() so that it always call follow_link() if the > > > inode is not a symlink... > > > > > > > I looked at this problem recently based on a request by some of our > > coreutils folks. A bit of the discussion is here: > > > > https://bugzilla.redhat.com/show_bug.cgi?id=533569 > > > > ...and earlier: > > > > https://bugzilla.redhat.com/show_bug.cgi?id=501848 > > > > Jim Meyering also brought this up on LKML: > > > > http://lkml.org/lkml/2009/11/4/451 > > > > I'm a little leery of triggering a mount for any server-side mountpoint > > that we just happen to have a peek at. That seems like it might get > > expensive. Suppose you had 1000 filesystems mounted under the root > > share here? > > For what it's worth, I'll admit that I ran across this just in > artificial testing--I'm not claiming it was causing me a real problem. > Understood. It's a bit of a dilemma... Clearly though, it's going to be a problem for some programs that need to deal with mountpoints (stuff like backup programs in particular). The problem though is that I don't think we want to trigger a bunch of submounts just because someone does a "ls -l" in a directory that holds a bunch of server-side mountpoints. The real problem I think is that we allocate new dev minor numbers at mount time. The ideal thing might be to have the client somehow pre-determine what the dev number of that mount would be without actually doing the mount. Then we could just present that device number in the stat call. -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
