Hi
On Tue, Aug 28, 2018 at 6:01 PM Daniel P. Berrangé <berra...@redhat.com> wrote:
>
> On Fri, Jul 13, 2018 at 03:09:08PM +0200, Marc-André Lureau wrote:
> > According to Daniel Berrange, fcntl() locks have better portable
> > semantics than lockf().
>
> Specifically I was referring to this from 'man lockf':
>
> On Linux, lockf() is just an interface on top of fcntl(2) locking.
> Many other systems implement lockf() in this way, but note that POSIX.1
> leaves the relationship between lockf() and fcntl(2) locks unspecified.
> A portable application should probably avoid mixing calls to these
> interfaces.
>
> IOW, if its just a shim around fcntl() on many systems, it is clearer
> if we just use fcntl() directly, as we then know how fcntl() locks will
> behave if they're on a network filesystem like NFS.
>
> > Use an exclusive lock on the first byte with fcntl().
> >
> > Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> > ---
> > util/oslib-posix.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> > index da1d4a3201..26b11490b9 100644
> > --- a/util/oslib-posix.c
> > +++ b/util/oslib-posix.c
> > @@ -92,6 +92,11 @@ bool qemu_write_pidfile(const char *pidfile, Error
> > **errp)
> > {
> > int pidfd;
> > char pidstr[32];
> > + struct flock lock = {
> > + .l_type = F_WRLCK,
> > + .l_whence = SEEK_SET,
> > + .l_len = 1,
> > + };
>
> For the same semantics as lockf we should use len == 0 (ie infinity)
>
ok
>
> Regards,
> Daniel
> --
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>
--
Marc-André Lureau
