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From: Johannes Sixt <j6t@kdbg.org>
To: Junio C Hamano <gitster@pobox.com>
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 20:13:56 +0100
Message-ID: <6beaf25f-1369-3e77-fd54-fdb5a1e63707@kdbg.org> (raw)
In-Reply-To: <xmqq5zj12qc2.fsf@gitster-ct.c.googlers.com>

Am 30.11.19 um 19:04 schrieb Junio C Hamano:
> "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
> writes:
> 
>>  * We now assign errno only when the call to CreateProcessW() failed.
> 
> Meaning the global variable 'errno' is left as it was (instead of
> getting cleared) when a system call succeeds?  That I think is the
> correct behaviour people who use the variable expect.

I hope you mean people who read the code. You cannot possibly mean
developers who expect that the run-command API keeps errno unchanged if
the calls were successful. I'm pretty sure they do not provide such a
guarantee.

> 
>>  * For good measure, we teach the err_win_to_posix() function to translate 
>>    ERROR_SUCCESS into the errno value 0.
> 
> So, I am not sure if this is a good idea---who are the callers of
> this function and why do they call it?  I would imagine that a
> caller who makes a system call, upon seeing a failure from the
> system call, calls this helper with the Windows error code it
> received from the system call so that errno can be updated with a
> POSIXy value.  If my imagination is correct, such a caller should
> not be assigning anything to errno if the underlying system call
> succeeds, i.e. returns ERROR_SUCCESS.  So a better solution might
> be for the function to BUG() when fed ERROR_SUCCESS to point fingers
> at the caller, no?

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.

-- Hannes

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-29 21:44 [PATCH 0/1] " 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 [this message]
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
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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