Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > When it goes wrong, what happens is that nfs_follow_remote_path() walks from > > the rootfh to the remote directory (/scratch) using vfs_path_lookup(). It > > passes LOOKUP_FOLLOW to vfs_path_lookup() to tell it to transit terminal > > symlinks and terminal automounts. Unfortunately, with the aforementioned > > commit, LOOKUP_FOLLOW now expressly does not follow terminal > > automounts. > > What is exactly happening here? By not following automounts how do we > end up with two mounts instead of one? I would have guessed the other > way round. Linux's NFS4 client performs a VFS path walk to resolve the path in the mount devname to the root fh of the new mount. This differs from NFS2/3 where the client asks the server's mountd to do it. With the situation I described, where you're attempting to directly mount a directory that's the root of a mount on the server (but not the root of the whole filesystem tree), you have a situation where the FSID changes as you walk through the tree. So, for example, assume "/" is on fsid 0 and "/scratch" is on fsid 1. Now, when NFS sees a change of fsid, it interpolates an automount point on the directory in which it saw the fsid change: / (FSID0) | | | scratch (S_AUTOMOUNT set) (FSID0) and, when triggered, d_automount will then create a new superblock for the new fsid and that will get mounted on the automount point: / (FSID0) | | | scratch ::::::::::::/(FSID1) (FSID0) | |-----|-----|-----| | | | | a b c d However, during the NFS4 root lookup pathwalk, because the root of fsid 1 is terminal in the path, with your patch it will not trigger automounting because none of LOOKUP_PARENT, _DIRECTORY, _OPEN or _CREATE are set. LOOKUP_FOLLOW was set and *that* used to be sufficient to force the automount. So what happens is that scratch from fsid 0 gets mounted rather than / from fsid 1 and this is an automount point. It will cause / from fsid 1 to be mounted eventually when someone goes into it, but then you have to do two unmounts to get rid of it instead of one. David -- 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
