On Wed, 27 Jan 2021 16:22:49 +0100 Miklos Szeredi <mszer...@redhat.com> wrote:
> On Wed, Jan 27, 2021 at 4:09 PM Greg Kurz <gr...@kaod.org> wrote: > > > > On Wed, 27 Jan 2021 15:09:50 +0100 > > Miklos Szeredi <mszer...@redhat.com> wrote: > > > The semantics of O_CREATE are that it can fail neither because the > > > file exists nor because it doesn't. This doesn't matter if the > > > exported tree is not modified outside of a single guest, because of > > > locking provided by the guest kernel. > > > > > > > Wrong. O_CREAT can legitimately fail with ENOENT if one element > > Let me make my statement more precise: > > O_CREAT cannot fail with ENOENT if parent directory exists throughout > the operation. > True, but I still don't see what guarantees guest userspace that the parent directory doesn't go away... I must have missed something. Please elaborate. > I'm sure this property is used all over the place in userspace code, > and hence should be supported in strict coherence (cache=none) mode. > > For relaxed coherence (cache=auto) I'm not quite sure. NFS is usually > the reference, we'd need to look into what guarantees it provides wrt. > O_CREAT and remote racing unlink. > > Thanks, > Miklos >
