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

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

* 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.

Dave

> 
> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org
> 




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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK