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From: Junio C Hamano <gitster@pobox.com>
To: Johannes Sixt <j6t@kdbg.org>
Cc: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org,
	Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: Re: [PATCH v2 0/2] Brown-bag fix on top of js/mingw-inherit-only-std-handles
Date: Sat, 30 Nov 2019 22:26:42 -0800	[thread overview]
Message-ID: <xmqqfti41rz1.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <xmqq1rtp2k01.fsf@gitster-ct.c.googlers.com> (Junio C. Hamano's message of "Sat, 30 Nov 2019 12:21:18 -0800")

Junio C Hamano <gitster@pobox.com> writes:

> Johannes Sixt <j6t@kdbg.org> writes:
>
>> Just like on POSIX the value of errno is indeterminate after a
>> successful system call, the value of GetLastError() indeterminate after
>> a successful Windows API call. Therefore, the err_win_to_posix() would
>> not be able to point at a bogus caller reliably. For this reason, let's
>> consider the function as a simple error code translator, and then
>> translating ERROR_SUCCESS to 0 (or is there ESUCCESS?) makes total sense.
>
> OK, that makes sense.

Actually, I do not think it makes that much sense, especially in the
context of this patch that claims to map success to 0 (assuming that
no E_ANYTHING has the value of zero---I am not sure POSIX gives such
a guarantee) "for good measure".

Even if Windows API makes the GetLastError() unusable after a
success call (unlike POSIX, where errno is left alone), the API
calls themselves would be signaling their own success or failure,
right?  So I would have imagined that any kosher caller would be
doing this:

	if (SomeWinAPI() != SUCCESS) {
		errno = err_win_to_posix(GetLastError());
		... possibly other reactions to the error ...
	}

If using a value grabbed from GetLastError() after a successfull
Windows API call is a wrong thing to do as you taught us in your
message, then an unconditional

	SomeWinAPI();
	errno = err_win_to_posix(GetLastError());

would be wrong anyway, and touching errno unconditionally, when the
previous call may have succeeded without checking, makes the pattern
doubly wrong, no?

Having said that, I do not expect myself to be looking into and
fixing anything in compat/*win*.[ch], so I do not care too deeply
either way, but I thought that it would help keep the sanity of
developers involved if we touched errno only upon a failure from an
underlying system.

Thanks.

  reply	other threads:[~2019-12-01  6:27 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-29 21:44 [PATCH 0/1] Brown-bag fix on top of js/mingw-inherit-only-std-handles Johannes Schindelin via GitGitGadget
2019-11-29 21:44 ` [PATCH 1/1] mingw: do set `errno` correctly when trying to restrict handle inheritance Johannes Schindelin via GitGitGadget
2019-11-29 23:02   ` Johannes Sixt
2019-11-30 22:06     ` Johannes Schindelin
2019-11-30 22:16       ` Johannes Sixt
2019-11-30 10:36 ` [PATCH v2 0/2] Brown-bag fix on top of js/mingw-inherit-only-std-handles Johannes Schindelin via GitGitGadget
2019-11-30 10:36   ` [PATCH v2 1/2] mingw: do set `errno` correctly when trying to restrict handle inheritance Johannes Schindelin via GitGitGadget
2019-11-30 10:36   ` [PATCH v2 2/2] mingw: translate ERROR_SUCCESS to errno = 0 Johannes Schindelin via GitGitGadget
2019-11-30 18:04   ` [PATCH v2 0/2] Brown-bag fix on top of js/mingw-inherit-only-std-handles Junio C Hamano
2019-11-30 19:13     ` Johannes Sixt
2019-11-30 20:11       ` Andreas Schwab
2019-11-30 20:23         ` Junio C Hamano
2019-11-30 20:43           ` Andreas Schwab
2019-11-30 21:22             ` Johannes Schindelin
2019-11-30 20:21       ` Junio C Hamano
2019-12-01  6:26         ` Junio C Hamano [this message]
2019-12-01  9:53           ` Johannes Schindelin
2019-12-02  6:07             ` Junio C Hamano
2019-12-02  9:05               ` Johannes Schindelin
2019-11-30 19:20   ` Johannes Sixt
2019-11-30 22:09     ` Junio C Hamano
2019-12-02 11:33   ` [PATCH v3 " Johannes Schindelin via GitGitGadget
2019-12-02 11:33     ` [PATCH v3 1/2] mingw: do set `errno` correctly when trying to restrict handle inheritance Johannes Schindelin via GitGitGadget
2019-12-02 11:33     ` [PATCH v3 2/2] mingw: translate ERROR_SUCCESS to errno = 0 Johannes Schindelin via GitGitGadget
2019-12-02 17:35     ` [PATCH v3 0/2] Brown-bag fix on top of js/mingw-inherit-only-std-handles Johannes Sixt
2019-12-02 19:04       ` Junio C Hamano
2019-12-03 12:04       ` Johannes Schindelin

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