On Tue, 2009-02-10 at 16:48 -0500, J. Bruce Fields wrote: > On Tue, Feb 10, 2009 at 01:31:48PM -0500, Trond Myklebust wrote: > > On Tue, 2009-02-10 at 10:58 -0500, J. Bruce Fields wrote: > > > On Mon, Feb 09, 2009 at 01:45:34PM -0500, Trond Myklebust wrote: > > > > The following two patches attempt to improve NFSv4's ability to look up > > > > the mount path on a remote server. > > > > > > > > The first patch adds VFS support for walking the remote path, using a > > > > temporary mount namespace to represent the server's namespace, so that > > > > symlinks > > > > > > I'm a bit confused about the symlink case--I take it you're assuming > > > that symlinks in the pseudofs should be interpreted as relative to the > > > server's namespace (in keeping with traditional implementations of > > > server exports), while symlinks elsewhere should continue to be > > > intepreted relative to the client's namespace. > > Maybe I shouldn't have said "symlinks in the pseudofs", as that's not > entirely well defined--a complicated namespace may transition between > "pseudofs" and "real" filesystems multiple times. So it's really a > statement about the client's mount behavior: symlinks found along the > mount path will be interpreted one way, symlinks found elsewhere > another. Right? > > Though put that way it's harder to decide what to store in a symlink, > since you can't necessarily control which paths a given client may > decide to mount. That has been the nature of an NFS mount path string since it was first introduced in NFSv2: it refers to the server namespace. People haven't complained about this previously, so why should we start changing the meaning of the mount path when we move to NFSv4? > > > Do the rfc's say anything about this? > > > > No, the RFCs say nothing, but interpreting symlinks as being relative to > > the server namespace would be consistent with the mount behaviour of > > NFSv2/v3. It also makes me uncomfortable to have a remote mount path > > that could refer back to the client's namespace: that would not be an > > NFS mount, but a local bind mount... > > Some may be surprised to find that /mntsymlink/ and /mnt/symlink/ will > be different after > > mount file:/path/symlink/ /mntsymlink/ > mount file:/path/ /mnt/ So, what then if I do ln -s ../foo /bar/baz/symlink on the server, then compare mount server:/bar/baz /mnt and mount server:/bar/baz/symlink /mnt Would you argue that those two should produce the same result? My interpretation would be as follows: In the first case, the symlink is visible as /mnt/symlink, and so 'cd /mnt/symlink' will take you to the local path '/foo' on the client. In the second case, I'd be very surprised if the mount code did anything other than to follow /bar/baz/symlink to remote path /bar/foo, and then mount that on '/mnt' If you agree that the above behaviour is correct, then how would you argue that replacing '/bar/baz/symlink' with an absolute symlink (i.e. 'ln -sf /bar/foo /bar/baz/symlink') should suddenly cause mount to do a bind mount? > I see your point, though it might also be an argument for continuing to > error out on symlinks. Again, why? We don't do that today with NFSv2/v3. > It could also be argued that if a given symlink is expected to be > interpreted on the server side, then the server should just go ahead and > do that for the client, rather than returning it as a symlink. How would the server distinguish between a client that is doing a lookup of a mount path and one that is looking up a normal path? > Seems worth at least mentioning to the ietf group, as different behavior > across different clients would be confusing. ...as would different behaviour across different versions of NFS. -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@xxxxxxxxxx www.netapp.com -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
