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    SubjectRe: [take25 1/6] kevent: Description.
    On Fri, Nov 24, 2006 at 03:05:31PM +0300, Evgeniy Polyakov (johnpol@2ka.mipt.ru) wrote:
    > On Thu, Nov 23, 2006 at 02:33:16PM -0800, Ulrich Drepper (drepper@redhat.com) wrote:
    > > Evgeniy Polyakov wrote:
    > > >+ int kevent_commit(int ctl_fd, unsigned int start,
    > > >+ unsigned int num, unsigned int over);
    > >
    > > I think we can simplify this interface:
    > >
    > > int kevent_commit(int ctl_fd, unsigned int new_tail,
    > > unsigned int over);
    > >
    > > The kernel sets the ring_uidx value to the 'new_tail' value if the tail
    > > pointer would be incremented (module wrap around) and is not higher then
    > > the current front pointer. The test will be a bit complicated but not
    > > more so than what the current code has to do to check for mistakes.
    > >
    > > This approach has the advantage that the commit calls don't have to be
    > > synchronized. If one thread sets the tail pointer to, say, 10 and
    > > another to 12, then it does not matter whether the first thread is
    > > delayed. If it will eventually be executed the result is simply a no-op
    > > and since second thread's action supersedes it.
    > >
    > > Maybe the current form is even impossible to use with explicit locking
    > > at userlevel. What if one thread, which is about to call kevent_commit,
    > > if indefinitely delayed. Then this commit request's value is never
    > > taken into account and the tail pointer is always short of what it
    > > should be.
    >
    > I like this interface, although current one does not allow special

    ...does not require...

    > synchronization in userspace, since it calculates if new commit is in
    > the area where previous commit was.
    > Will change for the next release.

    --
    Evgeniy Polyakov
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