On Mon, 2017-02-06 at 20:35 -0500, J. Bruce Fields wrote: > On Mon, Feb 06, 2017 at 04:10:11PM -0800, James Bottomley wrote: > > On Mon, 2017-02-06 at 16:52 -0500, J. Bruce Fields wrote: > > > On Mon, Feb 06, 2017 at 07:18:16AM -0800, James Bottomley wrote: > > > > On Mon, 2017-02-06 at 09:50 -0500, Theodore Ts'o wrote: > > > > > On Sun, Feb 05, 2017 at 10:46:23PM -0800, James Bottomley > > > > > wrote: > > > > > > Yes, I know the problem. However, I believe most current > > > > > > linux > > > > > > filesystems no longer guarantee stable, for the lifetime of > > > > > > the > > > > > > file, inode numbers. The usual docker container root is > > > > > > overlayfs, which, similarly doesn't support stable inode > > > > > > numbers. I see the odd complaint about docker with > > > > > > overlayfs > > > > > > having unstable inode numbers, but none seems to have any > > > > > > serious repercussions. > > > > > > > > > > Um, no. Most current linux file systems *do* guarantee > > > > > stable > > > > > inode numbers. For one thing, NFS would break horribly if > > > > > you > > > > > didn't have stable inode numbers. Never mind applications > > > > > which > > > > > depend on POSIX semantics. And you wouldn't be able to save > > > > > games in rogue or nethack, either. :-) > > > > > > > > I believe that's why we have the superblock export operations > > > > to > > > > manufacture unique filehandles in the absence of inode number > > > > stability. > > > > > > Where did you hear that? > > > > > > I'd expect an NFS client to handle non-unique filehandles > > > better than non-unique inode numbers. I believe our client will > > > -EIO > > > on encountering an inode number change (see > > > nfs_check_inode_attributes().) > > > > > > See also https://tools.ietf.org/html/rfc5661#section-10.3.4. > > > > Could you clarify your point a bit further, please? Both the > > check_inode_attributes() code and section 10.3.4 are talking about > > fileids, which are the things that are constructed in the > > export_ops > > No, the filehandle structure isn't discussed in the rfc at all, > that's > opaque to clients, and the "fileid" you see in the export code isn't > what's discussed here. > > The "fileid" here is an NFS attribute, really just the NFS protocol's > name for the inode number. The server code that returns fileid's: > > if (bmval0 & FATTR4_WORD0_FILEID) { > p = xdr_reserve_space(xdr, 8); > if (!p) > goto out_resource; > p = xdr_encode_hyper(p, stat.ino); > } > > The client getattr code: > > stat->ino = nfs_compat_user_ino64(NFS_FILEID(inode)); OK, I now believe we may be talking about different things. When I said > I believe that's why we have the superblock export operations to > manufacture unique filehandles in the absence of inode number > stability. I was talking about inode stability in the filesystem underlying the export. I believe you're talking about inode number stability guarantees of the nfs client code itself, which are unrelated to the inode number guarantees of the exported filesystem? James
