linux-kernel - Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

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Date:	Thu, 1 Mar 2007 11:38:06 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Chris Friesen <cfriesen@...tel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ulrich Drepper <drepper@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.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>,
	Zach Brown <zach.brown@...cle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

On Wed, Feb 28, 2007 at 11:42:24AM -0800, Davide Libenzi (davidel@...ilserver.org) wrote:
> On Wed, 28 Feb 2007, Chris Friesen wrote:
> 
> > Davide Libenzi wrote:
> > 
> > > struct async_syscall {
> > > 	unsigned long nr_sysc;
> > > 	unsigned long params[8];
> > > 	long *result;
> > > };
> > > 
> > > And what would async_wait() return bak? Pointers to "struct async_syscall"
> > > or pointers to "result"?
> > 
> > Either one has downsides.  Pointer to struct async_syscall requires that the
> > caller keep the struct around.  Pointer to result requires that the caller
> > always reserve a location for the result.
> > 
> > Does the kernel care about the (possibly rare) case of callers that don't want
> > to pay attention to result?  If so, what about adding some kind of
> > caller-specified handle to struct async_syscall, and having async_wait()
> > return the handle?  In the case where the caller does care about the result,
> > the handle could just be the address of result.
> 
> Something like this (with async_wait() returning asynid's)?
> 
> struct async_syscall {
> 	long *result;
> 	unsigned long asynid;
> 	unsigned long nr_sysc;
> 	unsigned long params[8];
> };

Having result pointer as NULL might imply that result is not interested
in and thus it can be discarded and event async syscall will not be
returned through aync_wait().
More flexible is having request flags field in the structure.
 
> - Davide
> 

-- 
	Evgeniy Polyakov
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