Subject: Re: [3/4] kevent: AIO, aio_sendfile() implementation.

From: Suparna Bhattacharya <[email-masked]>
Date: Mon, 31 Jul 2006 15:41:57 +0530

On Thu, Jul 27, 2006 at 11:44:23AM -0700, Ulrich Drepper wrote:
> Badari Pulavarty wrote:
> > Before we spend too much time cleaning up and merging into mainline -
> > I would like an agreement that what we add is good enough for glibc
> > POSIX AIO.
> 
> I haven't seen a description of the interface so far.  Would be good if

Did Sébastien's mail with the description help ? 

> it existed.  But I briefly mentioned one quirk in the interface about
> which Suparna wasn't sure whether it's implemented/implementable in the
> current interface.
> 
> If a lio_listio call is made the individual requests are handle just as
> if they'd be issue separately.  I.e., the notification specified in the
> individual aiocb is performed when the specific request is done.  Then,
> once all requests are done, another notification is made, this time
> controlled by the sigevent parameter if lio_listio.

Looking at the code in lio kernel patch, this should be already covered:

        if (iocb->ki_signo)
                __aio_send_signal(iocb);

+       if (iocb->ki_lio)
+               lio_check(iocb->ki_lio);

That is, it first checks the notification in the individual iocb, and then
the one for the LIO.

> 
> 
> Another feature which I always wanted: the current lio_listio call
> returns in blocking mode only if all requests are done.  In non-blocking
> mode it returns immediately and the program needs to poll the aiocbs.
> What is needed is something in the middle.  For instance, if multiple
> read requests are issued the program might be able to start working as
> soon as one request is satisfied.  I.e., a call similar to lio_listio
> would be nice which also takes another parameter specifying how many of
> the NENT aiocbs have to finish before the call returns.

I imagine the kernel could enable this by incorporating this additional
parameter for IOCB_CMD_GROUP in the ABI (in the default case this should be the
same as the total number of iocbs submitted to lio_listio). Now should the
at least NENT check apply only to LIO_WAIT or also to the LIO_NOWAIT
notification case ? 

BTW, the native io_getevents does support a min_nr wakeup already, except that
it applies to any iocb on the io_context, and not just a given lio_listio call.

Regards
Suparna

-- 
Suparna Bhattacharya ([email-masked])
Linux Technology Center
IBM Software Lab, India