Re: [PATCH v3 2/3] util: Get rid of virFileFlock()

[Martin Kletzander <mkletzan@xxxxxxxxxx>]

On Wed, Jul 29, 2020 at 02:20:50PM +0200, Andrea Bolognani wrote:
> On Wed, 2020-07-29 at 13:43 +0200, Martin Kletzander wrote:
> > +++ b/src/util/virresctrl.c
> > @@ -456,6 +456,8 @@ VIR_ONCE_GLOBAL_INIT(virResctrl);
> >  static int
> >  virResctrlLockWrite(void)
> >  {
> > +#ifndef WIN32
> > +
> >      int fd = open(SYSFS_RESCTRL_PATH, O_RDONLY | O_CLOEXEC);
> >
> >      if (fd < 0) {
> > @@ -463,13 +465,20 @@ virResctrlLockWrite(void)
> >          return -1;
> >      }
> >
> > -    if (virFileFlock(fd, true, false) < 0) {
> > +    if (flock(fd, LOCK_EX) < 0) {
> >          virReportSystemError(errno, "%s", _("Cannot lock resctrl"));
> >          VIR_FORCE_CLOSE(fd);
> >          return -1;
> >      }
> >
> >      return fd;
> > +
> > +#else /* WIN32 */
> > +
> > +    virReportSystemError(ENOSYS, "%s", _("Cannot lock resctrl"));
> > +    return -1;
> > +
> > +#endif
> >  }
> >
> >
> > @@ -484,10 +493,14 @@ virResctrlUnlock(int fd)
> >      if (VIR_CLOSE(fd) < 0) {
> >          virReportSystemError(errno, "%s", _("Cannot close resctrl"));
> >
> > +#ifndef WIN32
> > +
> >          /* Trying to save the already broken */
> > -        if (virFileFlock(fd, false, false) < 0)
> > +        if (flock(fd, LOCK_UN) < 0)
> >              virReportSystemError(errno, "%s", _("Cannot unlock resctrl"));
> >
> > +#endif
> > +
> >          return -1;
> >      }
>
> So in the end you decided to go for the nuclear option :D
>
> I'm okay with the approach, but I would prefer if you stubbed out the
> functions completely, eg.
>
>  #ifndef WIN32
>
>  static int
>  virResctrlLockWrite(void)
>  {
>      /* do stuff */
>  }
>
>  static int
>  virResctrlUnlock(int fd)
>  {
>      /* do stuff */
>  }
>
>  #else
>
>  static int
>  virResctrlLockWrite(void)
>  {
>      virReportSystemError(ENOSYS, "%s",
>                           _("resctrl locking is not supported "
>                             "on this platform"));
>      return -1;
>  }
>
>  static int
>  virResctrlUnlock(int fd)
>  {
>      virReportSystemError(ENOSYS, "%s",
>                           _("resctrl locking is not supported "
>                             "on this platform"));
>      return -1;
>  }
>
>  #endif
>
> Also, since AFAIU resctrl is Linux-only, perhaps a better
> preprocessor guard would be
>
>  #ifdef __linux__
>
> so that we (correctly) stub the functions out on FreeBSD and macOS
> too.

Well, in case they get any similar feature (since it is actually Intel-only
AFAIK) I just wanted to stub it out only for platforms where flock(2) is not
available.

> --
> Andrea Bolognani / Red Hat / Virtualization

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