Messages in this thread | | | Date | Thu, 23 Nov 2006 14:52:41 +0300 | From | Evgeniy Polyakov <> | Subject | Re: [take25 1/6] kevent: Description. |
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On Wed, Nov 22, 2006 at 03:46:42PM -0800, Ulrich Drepper (drepper@redhat.com) wrote: > Evgeniy Polyakov wrote: > >+ int kevent_wait(int ctl_fd, unsigned int num, __u64 timeout); > >+ > >+ctl_fd - file descriptor referring to the kevent queue > >+num - number of processed kevents > >+timeout - this timeout specifies number of nanoseconds to wait until > >there is + free space in kevent queue > >+ > >+Return value: > >+ number of events copied into ring buffer or negative error value. > > This is not quite sufficient. What we also need is a parameter which > specifies which ring buffer the code assumes is currently active. This > is just like the EWOULDBLOCK error in the futex. I.e., the kernel > doesn't move the thread on the wait list if the index has changed. > Otherwise asynchronous ring buffer filling is impossible. Assume this > > thread kernel > > get current ring buffer idx > > front and tail pointer the same > > add new entry to ring buffer > > bump front pointer > > call kevent_wait() > > > With the interface above this leads to a deadlock. The kernel delivered > the event and is done with it.
Kernel does not put there a new entry, it is only done inside kevent_wait(). Entries are put into queue (in any context), where they can be obtained from only kevent_wait() or kevent_get_events().
-- Evgeniy Polyakov - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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