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

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Date:	Tue, 13 Feb 2007 17:36:17 -0500
From:	Dmitry Torokhov <dtor@...ightbb.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Alan <alan@...rguk.ukuu.org.uk>, 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>,
	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>,
	Davide Libenzi <davidel@...ilserver.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 00/11] ANNOUNCE: "Syslets", generic asynchronous system call support

Hi Ingo,

On Tuesday 13 February 2007 15:39, Ingo Molnar wrote:
> 
> * Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> 
> > > What are the semantics of async sys_async_wait and async sys_async ?
> > 
> > Ooooohh. OpenVMS lives forever ;) Me likeee ;)
> 
> hm, i dont know OpenVMS - but googled around a bit for 'VMS 
> asynchronous' and it gave me this:
> 
>   http://en.wikipedia.org/wiki/Asynchronous_system_trap
> 
> is AST what you mean? From a quick read AST seems to be a signal 
> mechanism a bit like Unix signals, extended to kernel-space as well - 
> while syslets are a different 'safe execution engine' kind of thing 
> centered around the execution of system calls.
> 

That is only one of ways of notifying userspace of system call completion
on OpenVMS. Pretty much every syscall there exists in 2 flavors - async
and sync, for example $QIO and $QIOW or $ENQ/$ENQW (actually -W flavor
is async call + $SYNCH to wait for completion). Once system service call
is completed the OS would raise a so-called event flag and may also
deliver an AST to the process. Application may either wait for an
event flag/set of event flags (EFN) or rely on AST to get notification.

-- 
Dmitry
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