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Date: Tue, 10 Jul 2012 16:23:56 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH 4/5] Avoid unportable %m format
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To: Stefan Weil <sw@weilnetz.de>
Cc: Blue Swirl <blauwirbel@gmail.com>, qemu-devel@nongnu.org

On 07/10/2012 04:12 PM, Stefan Weil wrote:
> Am 10.07.2012 22:53, schrieb Anthony Liguori:
>> On 07/08/2012 06:51 AM, blauwirbel@gmail.com wrote:
>>> From: Blue Swirl<blauwirbel@gmail.com>
>>>
>>> Replace %m format with explicit call to standard strerror().
>>>
>>> Signed-off-by: Blue Swirl<blauwirbel@gmail.com>
>>
>> I would expect '%m' to be thread safe whereas strerror() isn't. I don't think
>> this change is actually good.
>>
>> You'd need to do something more clever with strerror_r() to be equivalent.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>
> Extract from the Linux manpage PRINTF(3):
>
> m (Glibc extension.) Print output of strerror(errno). No argument is required.

You're reading the docs too literally:

http://sourceware.org/git/?p=glibc.git;a=blob;f=stdio-common/vfprintf.c;h=d5690342536bc8cf948c786f663bb63f73f91f3a;hb=HEAD#l966

It uses strerror_r() and is thread-safe.  Converting to strerror() removes that 
safety.

Regards,

Anthony Liguori