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SubjectRe: [PATCH 0/2] eventfd: new EFD_STATE flag
On Wed, 26 Aug 2009, Avi Kivity wrote:

> On 08/26/2009 10:13 PM, Davide Libenzi 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));
> > }
> >
> >
> > On the hypervisor side:
> >
> > int read_state(int sfd) {
> > u64 cnt;
> >
> > read(sfd,&cnt, sizeof(cnt));
> > return state - 1;
> > }
> >
> >
>
> Hadn't though of read+write as set. While the 1+ is a little ugly, it's
> workable.

Pick what you want, as long as it always writes something != 0 :)


> I see no kernel equivalent to read(), but that's easily done.

Adding an in-kernel read based on "ctx", that is no problem at all.



- Davide




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