linux-kernel - Re: [patch 13/13] signal/timer/event fds v9

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Date:	Sun, 01 Apr 2007 18:06:56 +0300
From:	Avi Kivity <avi@...o.co.il>
To:	Davide Libenzi <davidel@...ilserver.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Zach Brown <zach.brown@...cle.com>,
	Benjamin LaHaise <bcrl@...ck.org>
Subject: Re: [patch 13/13] signal/timer/event fds v9 - KAIO eventfd support
 example ...

Davide Libenzi wrote:
> This is an example about how to add eventfd support to the current KAIO code,
> in order to enable KAIO to post readiness events to a pollable fd
> (hence compatible with POSIX select/poll). The KAIO code simply signals
> the eventfd fd when events are ready, and this triggers a POLLIN in the fd.
> This patch uses a reserved for future use member of the struct iocb to pass
> an eventfd file descriptor, that KAIO will use to post events every time
> a request completes. At that point, an aio_getevents() will return the
> completed result to a struct io_event.
> I made a quick test program to verify the patch, and it runs fine here:
>
> Index: linux-2.6.21-rc5.fds/include/linux/aio_abi.h
> ===================================================================
> --- linux-2.6.21-rc5.fds.orig/include/linux/aio_abi.h	2007-03-31 12:45:30.000000000 -0700
> +++ linux-2.6.21-rc5.fds/include/linux/aio_abi.h	2007-03-31 12:46:31.000000000 -0700
> @@ -84,7 +84,11 @@
>  
>  	/* extra parameters */
>  	__u64	aio_reserved2;	/* TODO: use this for a (struct sigevent *) */
> -	__u64	aio_reserved3;
> +	__u32	aio_reserved3;
> +	/*
> +	 * If different from 0, this is an eventfd to deliver AIO results to
> +	 */
> +	__u32	aio_resfd;
>  }; /* 64 bytes */
>  

What is the motivation for adding aio_resfd to an individual iocb 
instead of the entire io context?  It seems redundant, as you can 
already create multiple io contexts to wait on.

[also, minor nit: sys_eventfd() can legitimately return 0, but you're 
banning its use in aio.  userspace could easily dup() and close(), but...]

-- 
error compiling committee.c: too many arguments to function

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