Re: [PATCH 066/104] virtiofsd: passthrough_ll: add renameat2 support

[Daniel P . Berrangé]

On Mon, Jan 13, 2020 at 08:06:24PM +0000, Dr. David Alan Gilbert wrote:
> * Dr. David Alan Gilbert (address@hidden) wrote:
> > * Daniel P. Berrangé (address@hidden) wrote:
> > > On Thu, Dec 12, 2019 at 04:38:26PM +0000, Dr. David Alan Gilbert (git) 
> > > wrote:
> > > > From: Miklos Szeredi <address@hidden>
> > > > 
> > > > No glibc support yet, so use syscall().
> > > 
> > > It exists in glibc in my Fedora 31 install.
> > > 
> > > Presumably this is related to an older version
> > > 
> > > > Signed-off-by: Miklos Szeredi <address@hidden>
> > > > ---
> > > >  tools/virtiofsd/passthrough_ll.c | 10 ++++++++++
> > > >  1 file changed, 10 insertions(+)
> > > > 
> > > > diff --git a/tools/virtiofsd/passthrough_ll.c 
> > > > b/tools/virtiofsd/passthrough_ll.c
> > > > index 91d3120033..bed2270141 100644
> > > > --- a/tools/virtiofsd/passthrough_ll.c
> > > > +++ b/tools/virtiofsd/passthrough_ll.c
> > > > @@ -1083,7 +1083,17 @@ static void lo_rename(fuse_req_t req, fuse_ino_t 
> > > > parent, const char *name,
> > > >      }
> > > >  
> > > >      if (flags) {
> > > > +#ifndef SYS_renameat2
> > > >          fuse_reply_err(req, EINVAL);
> > > > +#else
> > > > +        res = syscall(SYS_renameat2, lo_fd(req, parent), name,
> > > > +                      lo_fd(req, newparent), newname, flags);
> > > > +        if (res == -1 && errno == ENOSYS) {
> > > > +            fuse_reply_err(req, EINVAL);
> > > > +        } else {
> > > > +            fuse_reply_err(req, res == -1 ? errno : 0);
> > > > +        }
> > > > +#endif
> > > 
> > > We should use the formal API if available as first choice
> > 
> > OK, done - I've kept the 'ifndef SYS_renameat2' that drops back to an
> > error for truly ancient cases; although I doubt everything else will
> > build on something that old.
> 
> Hmm, and this breaks on middle age distros;  older distros don't have it
> at all, new ones have both the syscall and the wrapper; but for the
> middle age ones they have the syscall but not the wrapper.
>
> Dan: What's your preference here; should I add a config fragment to
> detect the wrapper - it seems overkill rather than just reverting it
> until it becomes common.

What specific middle age distro in particular is affected ? My general
thought would be to /not/ support such distros. Focus on modern distros
since this is a brand new feature in QEMU, where we should try to
minimize support for legacy stuff at the start. But depending on the
distro impacted, the might be a reason to stay with SYS_..

Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|