linux-kernel - Re: [PATCH/RFC] Re: recvmmsg() timeout behavior strangeness [RESEND]

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Date:	Sat, 24 May 2014 08:13:18 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	David Miller <davem@...emloft.net>
CC:	mtk.manpages@...il.com, linux-kernel@...r.kernel.org,
	linux-man@...r.kernel.org, netdev@...r.kernel.org,
	neleai@...nam.cz, caitlin.bestler@...il.com, nhorman@...driver.com,
	eliedebrauwer@...il.com, steve@...gwyn.com,
	remi.denis-courmont@...ia.com, paul@...l-moore.com,
	chris.friesen@...driver.com
Subject: Re: [PATCH/RFC] Re: recvmmsg() timeout behavior strangeness [RESEND]

On 05/23/2014 09:55 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, May 23, 2014 at 03:00:55PM -0400, David Miller escreveu:
>> From: Arnaldo Carvalho de Melo <acme@...nel.org>
>> Date: Wed, 21 May 2014 18:05:35 -0300
> 
>>> But after thinking a bit more, looks like we need to do that, please
>>> take a look at the attached patch to see if it addresses the problem.
> 
>>> Mostly it adds a new timeop to the per protocol recvmsg()
>>> implementations, that, if not NULL, should be used instead of
>>> SO_RCVTIMEO.
> 
>>> since the underlying recvmsg implementations already check that timeout,
>>> return what is remaining, that will then be used in subsequent recvmsg
>>> calls, at the end we just convert it back to timespec format.
> 
>>> In most cases it is just passed to skb_recv_datagram, that will check
>>> the pointer, use it and update if not NULL.
> 
>>> Should have no problems, but I only did a boot with a system with this
>>> patch applied, no problems noticed on a normal desktop session, ssh,
>>> etc.
>  
>> This looks fine to me, but I have a small request:
>  
>> +	return noblock ? 0 : timeop ? *timeop : sk->sk_rcvtimeo;
>  
>> I keep forgetting which way these expressions associate, so if you could
>> parenthesize the innermost ?: I'd appreciate it. :)
> 
> Ok, I actually wrote a sample program to verify that these ternaries did
> what I meant 8)
> 
> I'll finish the cset log and do this clarification change.
> 
> Would be great to get Acked-by tags from the original reporter, Michael
> and whoever had a look at this change, if possible. Michael, Elie?

Arnaldo, I already sent you a reply (will reping on that one),
but got no response. My light testing got the expected results,
but I still had one question about the semantics.

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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