On Thu, 27 Aug 2009, Michael S. Tsirkin wrote:
> On Thu, Aug 27, 2009 at 07:21:49AM -0700, Davide Libenzi wrote:
> > On Thu, 27 Aug 2009, Paolo Bonzini wrote:
> >
> > > > Ok, so why not using the eventfd counter as state?
> > > > On the device side:
> > > >
> > > > void write_state(int sfd, int state) {
> > > > u64 cnt;
> > > >
> > > > /* Clear the current state, sfd is in non-blocking mode */
> > > > read(sfd,&cnt, sizeof(cnt));
> > > > /* Writes new state */
> > > > cnt = 1 + !!state;
> > > > write(sfd,&cnt, sizeof(cnt));
> > > > }
> > >
> > > It's interesting [no sarcasm intended, mind] that EFD_SEMAPHORE was
> > > added exactly to avoid a read+write combination for the case of
> > > decrementing a value.
> >
> > Like I repeated 25 times already, EFD_SEMAPHORE was added, because a
> > *semaphore* is a pretty widely known and used abstraction.
>
> what about an atomic variable, btw? does it make sense to implement
> write that does compare and exchange?
It is surprising to me, that is front of a workable solution w/out any
use-once additions, yet you want to try to add optimizations and new
ad-hoc abstractions to user visible interfaces.
Now, you tell me what an atomic variable has to do with an eventfd.
- Davide
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