2013/5/14 Jeff Layton <jlayton@xxxxxxxxxx>: > On Fri, 10 May 2013 10:27:54 -0400 > Jeff Layton <jlayton@xxxxxxxxxx> wrote: > >> On Fri, 10 May 2013 16:13:30 +0200 >> Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >> >> > Hi, >> > >> > A while ago this was discussed: >> > >> > http://thread.gmane.org/gmane.linux.kernel.cifs/7779 >> > >> > This is essentially a regression introduced by the shared superblock >> > changes in 3.0 and several SUSE customers are complaining about it. >> > I've created a temporary fix which reverts 29 commits related to the >> > shared superblock changes. It works, but it's obviously not a >> > permanent fix, especially since we definitely don't want to diverge >> > from mainline. >> > >> > Is this issue being worked on? Don't other distros have similar reports? >> > >> > Thanks, >> > Miklos >> >> I don't know of anyone currently working on it. There are a couple of >> possible approaches to fixing it, I think: >> >> 1) if the dentries to get down to the root of the mount don't already >> exist, then attach some sort of "placeholder" inode that can be fleshed >> out later if and when the dentry is accessed via other means. >> >> 2) do something like what NFS does (see commit 54ceac45). This becomes >> a bit more complicated due to the fact that the server may not hand out >> real inode numbers and we sometimes have to fake them up. >> >> #1 is probably simpler to implement, but I'll confess that I haven't >> thought through all of the potential problems with it. >> > > So, giving this some more thought, I think #2 is really the correct way > to fix this. Here's the main problem though: > > Suppose someone mounts: > > //server/share/foo/bar/baz > > We make the sb->s_root point to the top level share, and then create a > disconnected dentry for "baz" to return from ->mount. > > Then, a little while later, //server/share gets mounted separately and > a user walks down to /foo/bar/baz within the same share. > > How do we ensure that we don't end up with two "baz" dentries in this > situation? With NFS, we can be reasonably sure that there's a 1:1 > correspondance of filehandle to inode. > > Under CIFS, it's possible that it's faking up inode numbers if the > server doesn't provide them via a UniqueID field. The only real > identifying info we have for the inode in that case is the pathname. > > Perhaps we'd be best off to just rip out the sb sharing after all. > Getting all of the corner cases right when the protocol and server > implementations are so problematic is really, really difficult. > > If we do go that route, then the fscache code will need some work since > it uses the sharename as a sb cookie. Another option is to add mount options shared and nonshared (default) like NFS already has and let users use sharing capability if the permissions on server allow walking through a share path to a mount root. -- Best regards, Pavel Shilovsky. -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
