On Thu, Jul 07, 2011 at 01:46:21PM -0700, Paul Nienaber wrote: > So, much like coreutils' du (which also shouldn't), xfs_quota > traverses bind mountpoints both when doing 'project -s' and 'project > -C', and probably also 'project -c' although I haven't tested it. > Testcase and output follows. How is a userspace traversal supposed to detect the fact it crosses a bind mount when it enters a directory? If you bind a directory from the same filesystem, stat(2) on the file returns -identical- information regardless of whether you are inside or outside the bind mount. So the normal mechanisms (e.g. st_dev changes) for detecting such a mount point traversal simply don't work. So the first question is whether we should be trying to detect bind mounts within the same filesystem and handling them for project quotas? I don't know the answer to that. Indeed: $ find . . ./projects ./projects/foo ./projects/foo/chroot find: File system loop detected; `./projects/foo/chroot/scratch' is part of the same file system loop as `.'. ./projects/bar ./projects/bar/foo ./baz find has some way of detecting such cases, but it doesn't do it via any special syscalls, nor does the newfstatat(AT_SYMLINK_NOFOLLOW) call it does return an error. And it does it regardless of whether the -xdev option is specified or not. So it must have some form of internal logic for detecting such loopy filesystem constructs. However, operations such as "chmod -R" do *not* detect this situation: $ sudo chown -R -v dave:dave * ownership of `baz' retained as dave:dave changed ownership of `projects/foo/chroot/scratch/projects/foo/chroot/scratch' to dave:dave changed ownership of `projects/foo/chroot/scratch/projects/foo/chroot' to dave:dave changed ownership of `projects/foo/chroot/scratch/projects/foo' to dave:dave changed ownership of `projects/foo/chroot/scratch/projects/bar/foo' to dave:dave changed ownership of `projects/foo/chroot/scratch/projects/bar' to dave:dave changed ownership of `projects/foo/chroot/scratch/projects' to dave:dave ownership of `projects/foo/chroot/scratch/baz' retained as dave:dave changed ownership of `projects/foo/chroot/scratch' to dave:dave changed ownership of `projects/foo/chroot' to dave:dave changed ownership of `projects/foo' to dave:dave ownership of `projects/bar/foo' retained as dave:dave ownership of `projects/bar' retained as dave:dave changed ownership of `projects' to dave:dave It's totally unclear what the behaviour of xfs_quota should be, because operations that change user and group quotas are completely ignorant of bind mounts. So if we decide bind mounts are important to detect, the second question is how do we detect bind mount point traversals in a reliable manner that doesn't involve adding significant overhead to the directory traversal code? I don't know the answer to that, either, and if you care about this enough I guess you'll go and look up what find does and tell us about it ;) Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
