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Date: Mon, 8 Jan 2018 10:05:42 -0800 (PST)
From: Don Lewis <truckman@FreeBSD.org>
Subject: Re: Is it considered to be ok to not check the return code of
 close(2) in base?
To: Eugene Grosbein <eugen@grosbein.net>
cc: Eric van Gyzen <eric@vangyzen.net>, Brooks Davis <brooks@freebsd.org>,
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 Freebsd hackers list <freebsd-hackers@freebsd.org>
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On  8 Jan, Eugene Grosbein wrote:
> 08.01.2018 23:13, Eric van Gyzen wrote:
> 
>> Right, which is the reason such bugs are hard to diagnose.  Optionally
>> killing the process on close->EBADF would help find buggy code when
>> another thread did NOT re-open the file descriptor between the two close
>> calls.
> 
> Wouldn't "close(f); assert(errno != EBADF);" be better?

That can produce false positives.  The close() might be successful,
in which case it will not touch errno, and errno might have been set
to EBADF by some earlier operation.