Date: Mon, 8 Jan 2018 10:13:15 -0600 From: Eric van Gyzen <eric@vangyzen.net> To: Eugene Grosbein <eugen@grosbein.net>, Brooks Davis <brooks@freebsd.org>, Alan Somers <asomers@freebsd.org> Cc: Yuri <yuri@rawbw.com>, Ian Lepore <ian@freebsd.org>, Freebsd hackers list <freebsd-hackers@freebsd.org> Subject: Re: Is it considered to be ok to not check the return code of close(2) in base? Message-ID: <d75e9334-4da1-125c-73a5-1115003d12b5@vangyzen.net> In-Reply-To: <5A5002D9.9080205@grosbein.net> References: <24acbd94-c52f-e71a-8a96-d608a10963c6@rawbw.com> <1514572041.12000.7.camel@freebsd.org> <CAOtMX2jSonHQ9xzVD3Q9XS2twBm_CT3Tquwn%2Bf6zmc7aV0QerQ@mail.gmail.com> <20180105221330.GD95035@spindle.one-eyed-alien.net> <5A4FF989.1040709@grosbein.net> <7b977409-96ee-5acb-60d0-3b0e124495f0@vangyzen.net> <5A5002D9.9080205@grosbein.net>
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On 01/05/2018 16:57, Eugene Grosbein wrote: > 06.01.2018 5:26, Eric van Gyzen wrote: > >>>>> I would argue the opposite. There are very few reasons why close(s) would >>>>> ever fail, and the most likely is EBADF. EBADF indicates a programming >>>>> bug, like a double close or use of an uninitialized variable. Those could >>>>> easily turn into worse bugs in the future. So I think the best course of >>>>> action is to check the return code, assert() on EBADF, and ignore, or >>>>> possibly log, other errors. >>>> >>>> For this specific case, I think there would be value in an option to >>>> have the kernel kill any process that calls close(fd) where fd != -1 >>>> where EBADF would be returned. >>> >>> A medicine should not be worse worse than the disease, imho. >> >> In a multi-threaded application, a double-close can close completely >> unrelated file descriptors, which can be a nightmare to diagnose. In >> that case, death by signal is far better than the disease. > > A kernel cannot know if close() was called for "unrealated" but correct file descriptor. 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. Eric
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