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Re: bash: Correct usage of F_SETFD


From: Eric Blake
Subject: Re: bash: Correct usage of F_SETFD
Date: Mon, 22 Nov 2010 15:27:06 -0700
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On 11/22/2010 03:16 PM, Chet Ramey wrote:
>> include/filecntl.h in bash-4.1 has following:
>>
>> #define SET_CLOSE_ON_EXEC(fd)  (fcntl ((fd), F_SETFD, FD_CLOEXEC))
>>
>> Is that really the correct/intended usage of F_SETFD ?
> 
>      F_SETFD            Set the close-on-exec flag associated with fildes to
>                         the low order bit of arg (0 or 1 as above).
> 
>> If kernel ever adds a new flag to the fd, this would end up clearing the
>> other new flag right ?
>>
>> Shouldn't bash use F_GETFD to get the current flags and set/clear just
>> the FD_CLOEXEC bit ?
> 
> I suppose it would matter if there are systems that have more than one
> flag value.

In practice, there aren't any such systems; but POSIX warns that current
practice is no indicator of future systems, and that read-modify-write
is the only way to use F_SETFD.

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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