Re: [Qemu-devel] [Virtio-fs] [PATCH] virtiofsd: fix compile error if 'F_OFD_GETLK' not defined

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Dr. David Alan Gilbert (dgilbert@redhat.com) wrote:
> * Eric Blake (eblake@redhat.com) wrote:
> > On 7/29/19 7:27 PM, piaojun wrote:
> > > Use F_GETLK for fcntl when F_OFD_GETLK not defined.
> > 
> > Which system are you hitting this problem on?
> > 
> > The problem with F_GETLK is that it is NOT as safe as F_OFD_GETLK.
> > 
> > We already have fcntl_op_getlk and qemu_probe_lock_ops() in util/osdep.c
> > to not only determine which form to use, but also to emit a warning to
> > the end user if we had to fall back to the unsafe F_GETLK. Why is your
> > code not reusing that logic?
> > 
> > > 
> > > Signed-off-by: Jun Piao <piaojun@huawei.com>
> > > ---
> > >  contrib/virtiofsd/passthrough_ll.c | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> > > 
> > > diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
> > > index 9ae1381..757785b 100644
> > > --- a/contrib/virtiofsd/passthrough_ll.c
> > > +++ b/contrib/virtiofsd/passthrough_ll.c
> > > @@ -1619,7 +1619,11 @@ static void lo_getlk(fuse_req_t req, fuse_ino_t ino,
> > >  		return;
> > >  	}
> > > 
> > > +#ifdef F_OFD_GETLK
> > >  	ret = fcntl(plock->fd, F_OFD_GETLK, lock);
> > > +#else
> > > +	ret = fcntl(plock->fd, F_GETLK, lock);
> > > +#endif
> > 
> > Hmm. Since this is in contrib, you are trying to compile something that
> > is independent of util/osdep.c (at least, I assume that's the case, as
> > contrib/virtiofsd/ is not even part of qemu.git master yet - in which
> > case, why is this not being squashed in to the patch introducing that
> > file, rather than sent standalone).  On the other hand, that raises the
> > question - who is trying to use virtiofsd on a kernel that is too old to
> > provid F_OFD_GETLK?  Isn't the whole point of virtiofsd to be speeding
> > up modern usage, at which point an old kernel is just gumming up the
> > works?  It seems like you are better off letting compilation fail on a
> > system that is too old to support decent F_OFD_GETLK, rather than
> > silently falling back to something that is unsafe.
> 
> It is, but I guess the answer here is someone wanted to build on RHEL7.

although looking at the tools it went in 7.6

Dave

> Dave
> 
> > 
> > -- 
> > Eric Blake, Principal Software Engineer
> > Red Hat, Inc.           +1-919-301-3226
> > Virtualization:  qemu.org | libvirt.org
> > 
> 
> 
> 
> 
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> > Virtio-fs@redhat.com
> > https://www.redhat.com/mailman/listinfo/virtio-fs
> 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 
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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK