On 7/9/20 6:30 PM, Andrea Bolognani wrote:
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 :)
Just realized that for exclusive (aka write) lock, the FD must be opened
for writing (working on patches for the following report [1] and been
experimenting a bit and that's what I'm seeing).
1: https://www.redhat.com/archives/libvir-list/2020-July/msg00451.html
Michal
