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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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