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

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Message-ID: <Pine.LNX.4.64.0702131526410.32055@alien.or.mcafeemobile.com>
Date:	Tue, 13 Feb 2007 15:28:03 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Ingo Molnar <mingo@...e.hu>
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

On Tue, 13 Feb 2007, Ingo Molnar wrote:

> * 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.

That works too. I was thinking about identifying syslets with the 
userspace ptr, but the TID is fine too.



> 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. )

Yup.



- Davide


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