[PATCH] resctrl: Do not open directory for writing

[Andrea Bolognani]

On Thu, 2020-07-09 at 13:44 +0200, Martin Kletzander wrote:
> On Thu, Jul 09, 2020 at 12:50:38PM +0200, Andrea Bolognani wrote:
> > it seems to me that this change entirely flipped the semantics of
> > the lock.
> 
> Yep, you're right.  When you have a lock that has boolean as a parameter I think
> the boolean should indicate whether the lock is writable, but maybe the proper
> and most readable solution would be virFileFlockShareable() and
> virFileFlockExclusive() to avoid any misconception in the future[2].  Given the
> fact that there are no (and most probably won't be) any other users of flock(2)
> and given the fact that resctrl is also pretty niche feature, I don't have any
> preference.  Also I feel like after some time I'm a little bit rusty with C and
> the libvirt codebase (and most importantly the reasoning and decisions) has
> changed a bit, so I'll leave the decision on how to deal with that on someone
> else.  I'm happy to provide the patches when clear decision is made.

Either

  virFileFlockExclusive(fd)
  virFileFlockShared(fd)

or

  virFileFlock(fd, VIR_FILE_FLOCK_EXCLUSIVE)
  virFileFlock(fd, VIR_FILE_FLOCK_SHARED)

would work. I like the latter better because it's closer to the
original flock(), which it ultimately acts as a very thin wrapper
around of. I'm actually unclear why we'd have the last argument in
the first place: personally I'd just use

  virFileFlock(fd, VIR_FILE_FLOCK_UNLOCK)

and keep things as unambiguous as they can be.

This is all bikeshedding, of course: what actually matters is making
that lock exclusive once again :)

-- 
Andrea Bolognani / Red Hat / Virtualization