On Sun, 2019-04-28 at 09:45 -0400, Amir Goldstein wrote: > On Sun, Apr 28, 2019 at 8:09 AM Jeff Layton <jlayton@xxxxxxxxxx> > wrote: > > On Sat, 2019-04-27 at 16:16 -0400, Amir Goldstein wrote: > > > [adding back samba/nfs and fsdevel] > > > > > > > cc'ing Pavel too -- he did a bunch of work in this area a few years > > ago. > > > > > On Fri, Apr 26, 2019 at 6:22 PM Jeff Layton <jlayton@xxxxxxxxxx> > > > wrote: > > > > On Fri, 2019-04-26 at 10:50 -0400, J. Bruce Fields wrote: > > > > > On Fri, Apr 26, 2019 at 04:11:00PM +0200, Amir Goldstein > > > > > wrote: > > > > > > On Fri, Apr 26, 2019, 4:00 PM J. Bruce Fields < > > > > > > bfields@xxxxxxxxxxxx> wrote: > > > > > > > > > > That said, we could also look at a vfs-level mount option that > > > > would > > > > make the kernel enforce these for any opener. That could also > > > > be useful, > > > > and shouldn't be too hard to implement. Maybe even make it a > > > > vfsmount- > > > > level option (like -o ro is). > > > > > > > > > > Yeh, I am humbly going to leave this struggle to someone else. > > > Not important enough IMO and completely independent effort to the > > > advisory atomic open&lock API. > > > > Having the kernel allow setting deny modes on any open call is a > > non- > > starter, for the reasons Bruce outlined earlier. This _must_ be > > restricted in some fashion or we'll be opening up a ginormous DoS > > mechanism. > > > > My proposal was to make this only be enforced by applications that > > explicitly opt-in by setting O_SH*/O_EX* flags. It wouldn't be too > > difficult to also allow them to be enforced on a per-fs basis via > > mount > > option or something. Maybe we could expand the meaning of '-o mand' > > ? > > > > How would you propose that we restrict this? > > > > Our communication channel is broken. > I did not intend to propose any implicit locking. > If samba and nfsd can opt-in with O_SHARE flags, I do not > understand why a mount option is helpful for the cause of > samba/nfsd interop. > > If someone else is interested in samba/local interop than > yes, a mount option like suggested by Pavel could be a good option, > but it is an orthogonal effort IMO. If an NFS client 'opts in' to set share deny, then that still makes it a non-optional lock for the other NFS clients, because all ordinary open() calls will be gated by the server whether or not their application specifies the O_SHARE flag. There is no flag in the NFS protocol that could tell the server to ignore deny modes. IOW: it would suffice for 1 client to use O_SHARE|O_DENY* to opt all the other clients in. -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
