linux-kernel - Re: include/linux/aio_abi.h and IOCB_CMD

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Date:	Fri, 05 Jun 2009 00:53:43 +0200
From:	Goswin von Brederlow <goswin-v-b@....de>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Goswin von Brederlow <goswin-v-b@....de>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: include/linux/aio_abi.h and IOCB_CMD_POLL

Davide Libenzi <davidel@...ilserver.org> writes:

> On Thu, 4 Jun 2009, Goswin von Brederlow wrote:
>
>> Miklos Szeredi <miklos@...redi.hu> writes:
>> 
>> > On Thu, 04 Jun 2009, Goswin von Brederlow wrote:
>> >> 3) Are there any alternatives to libaio that don't use threads and
>> >>    support polling?
>> >
>> > There are the poll, select and epoll interfaces that block, but are
>> > able to multiplex events from many file descriptors.
>> 
>> Unfortunately libaio does not use an fd to pass events between user
>> and kernel space so one can't use poll, select or epoll to wait for
>> /dev/fuse or libaio to have some work pending. And none of them
>> replace libaio functionality in respect to read/write.
>
> You can use the eventfd bridge between epoll/poll/select and AIO, that is 
> available by quite some time.
> This is an old example I made when the patch was posted:
>
> http://www.xmailserver.org/eventfd-aio-test.c
>
> This uses direct syscall interface, but you get the idea on how to do that 
> with libaio (that I never used).

Thanks. That example explains it nicely. There really should be
comments in libaio.h and an /usr/share/doc/libaio/examples/.

In case you wonder the libaio just wraps the system calls and provides
helpers in libaio.h. Basically the first 200 lines of the example are
libaio.h. Not 1:1 but nearly. The only difference is that io_prep_* do
not take an eventfd argument but there is

static inline void io_set_eventfd(struct iocb *iocb, int eventfd)

instead.


Now I have 2 ways of doing this. Always with the choices. :)

MfG
        Goswin
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