linux-kernel - Re: [patch 2/5] signalfd v2

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Date:	Sat, 31 Mar 2007 01:24:22 +0200
From:	Denis Vlasenko <vda.linux@...glemail.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Michael K. Edwards" <medwards.linux@...il.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	"David M. Lloyd" <dmlloyd@...rg.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 2/5] signalfd v2 - signalfd core ...

On Thursday 08 March 2007 18:28, Linus Torvalds wrote:
> The sad part is that there really is no reason why the BSD crowd couldn't 
> have done recvmsg() as an "extended read with per-system call flags", 
> which would have made things like O_NONBLOCK etc unnecessary, because you 
> could do it just with MSG_DONTWAIT..

Wait a second here... O_NONBLOCK is not just unnecessary - it's buggy!

Try to do nonblocking read from stdin (fd #0) -
* setting O_NONBLOCK with fcntl will set it for all other processes
  which has the same stdin!
* trying to reset O_NONBLOCK after the read doesn't help (think kill -9)
* duping fd #0 doesn't help because O_NONBLOCK is not per-fd,
  it's shared just like filepos.

I really like that trick with recvmsg + MSG_DONTWAIT instead.
--
vda
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