On Fri, Dec 03, 2010 at 04:45:27PM -0500, Josef Bacik wrote: > So now that I've actually looked at everything, it looks like the semantics are > all right for subvolumes > > 1) readdir - we return the root id in d_ino, which is unique across the fs Though Michael Vrable pointed out an apparent collision with "normal" inode numbers on the parent filesystem? > 2) stat - we return 256 for all subvolumes, because that is their inode number > 3) dev_t - we setup an anon super for all volumes, so they all get their own > dev_t, which is set properly for all of their children, see below > > [root@test1244 btrfs-test]# stat . > File: `.' > Size: 20 Blocks: 8 IO Block: 4096 directory > Device: 15h/21d Inode: 256 Links: 1 > Access: (0555/dr-xr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root) > Access: 2010-12-03 15:35:41.931679393 -0500 > Modify: 2010-12-03 15:35:20.405679493 -0500 > Change: 2010-12-03 15:35:20.405679493 -0500 > > [root@test1244 btrfs-test]# stat foo > File: `foo' > Size: 12 Blocks: 0 IO Block: 4096 directory > Device: 19h/25d Inode: 256 Links: 1 > Access: (0700/drwx------) Uid: ( 0/ root) Gid: ( 0/ root) > Access: 2010-12-03 15:35:17.501679393 -0500 > Modify: 2010-12-03 15:35:59.150680051 -0500 > Change: 2010-12-03 15:35:59.150680051 -0500 > > [root@test1244 btrfs-test]# stat foo/foobar > File: `foo/foobar' > Size: 0 Blocks: 0 IO Block: 4096 regular empty file > Device: 19h/25d Inode: 257 Links: 1 > Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root) > Access: 2010-12-03 15:35:59.150680051 -0500 > Modify: 2010-12-03 15:35:59.150680051 -0500 > Change: 2010-12-03 15:35:59.150680051 -0500 > > So as far as the user is concerned, everything should come out right. Obviously > we had to do the NFS trickery still because as far as VFS is concerned the > subvolumes are all on the same mount. So the question is this (and really this > is directed at Christoph and Bruce and anybody else who may care), is this good > enough, or do we want to have a seperate vfsmount for each subvolume? Thanks, For nfsd's purposes, we need to be able find out about filesystems in two different ways: 1. Lookup by filehandle: we need to be able to identify which subvolume we're dealing with from a filehandle. 2. Lookup by path: we need to notice when we cross into a subvolume. Looks like #1 already works. Not #2: the current nfsd code just checks for mountpoints. We could modify nfsd to also check whether dev_t changed each time it did a lookup. I suppose it would work, though it's annoying to have to do it just for the case of btrfs. As far as I can tell, crossing into a subvolume is like crossing a mountpoint in every way except for the lack of a separate vfsmount. I'd worry that the inconsistency will end up requiring more special cases down the road, but I don't have any in mind. --b. -- 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
