linux-kernel - Re: [patch 00/11] ANNOUNCE: "Syslets", generic asynchronous system call support

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Message-ID: <20070213221052.GE22104@elte.hu>
Date:	Tue, 13 Feb 2007 23:10:52 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 00/11] ANNOUNCE: "Syslets", generic asynchronous system call support


* Davide Libenzi <davidel@...ilserver.org> wrote:

> > If this is going to be a generic AIO subsystem:
> > 
> > - Cancellation of peding request
> 
> What about the busy_async_threads list becoming a hash/rb_tree indexed 
> by syslet_atom ptr. A cancel would lookup the thread and send a signal 
> (of course, signal handling of the async threads should be set 
> properly)?

well, each async syslet has a separate TID at the moment, so if we want 
a submitted syslet to be cancellable then we could return the TID of the 
syslet handler (instead of the NULL) in sys_async_exec(). Then 
user-space could send a signal the old-fashioned way, via sys_tkill(), 
if it so wishes.

the TID could also be used in a sys_async_wait_on() API. I.e. it would 
be a natural, readily accessible 'cookie' for the pending work. TIDs can 
be looked up lockless via RCU, so it's reasonably fast as well.

( Note that there's already a way to 'signal' pending syslets: do_exit() 
  in the user context will signal all async contexts (which results in 
  -EINTR of currently executing syscalls, wherever possible) and will 
  tear them down. But that's too crude for aio_cancel() i guess. )

	Ingo
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