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From: Jeff King <peff@peff.net>
To: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, "SZEDER Gábor" <szeder.dev@gmail.com>,
	"Alexandr Miloslavskiy" <alexandr.miloslavskiy@syntevo.com>,
	"Johannes Schindelin" <johannes.schindelin@gmx.de>,
	"Junio C Hamano" <gitster@pobox.com>
Subject: Re: [PATCH v3 1/1] vreportf(): avoid relying on stdio buffering
Date: Tue, 29 Oct 2019 16:32:59 -0400	[thread overview]
Message-ID: <20191029203259.GB12337@sigill.intra.peff.net> (raw)
In-Reply-To: <fce0894ee46f737322551b51edf5cd2a53413a50.1572379280.git.gitgitgadget@gmail.com>

On Tue, Oct 29, 2019 at 08:01:20PM +0000, Johannes Schindelin via GitGitGadget wrote:

> diff --git a/usage.c b/usage.c
> index 2fdb20086b..471efb2de9 100644
> --- a/usage.c
> +++ b/usage.c
> @@ -9,14 +9,21 @@
>  void vreportf(const char *prefix, const char *err, va_list params)
>  {
>  	char msg[4096];
> -	char *p;
> +	size_t off = strlcpy(msg, prefix, sizeof(msg));
> +	char *p, *pend = msg + sizeof(msg);
>  
> -	vsnprintf(msg, sizeof(msg), err, params);
> -	for (p = msg; *p; p++) {
> +	p = off < pend - msg ? msg + off : pend - 1;
> +	if (vsnprintf(p, pend - p, err, params) < 0)
> +		*p = '\0'; /* vsnprintf() failed, clip at prefix */
> +
> +	for (; p != pend - 1 && *p; p++) {
>  		if (iscntrl(*p) && *p != '\t' && *p != '\n')
>  			*p = '?';
>  	}

This version looks OK to me. Some bikeshedding:

  - I suspect it may be more readable to just stick to offsets instead
    of pointers, since that's what strlcpy() and vsnprintf() give us.

  - I don't think "p == pend - 1" can ever trigger, since either
    vsnprintf() or we will have just written a NUL.

  - Do we need to contend with vsnprintf() return a negative value in
    general in our codebase? We already BUG() on it elsewhere. Yes, that
    BUG() would try to write via this code path, but it implies to me
    that we've already dealt with any such broken vsnprintf()
    implementations (via compat/snprintf.c).

If you're sick of bikeshedding, though, I can live without any of those
being addressed.

> +	*(p++) = '\n'; /* we no longer need a NUL */
> +	fflush(stderr);
> +	write_in_full(2, msg, p - msg);

One non-bikeshed question: would fprintf() on some platforms have sent
"\r\n", which is no longer happening with our write()? Do we need to
care about that?

-Peff

  reply	other threads:[~2019-10-29 20:33 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-28 15:00 [PATCH 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget
2019-10-28 15:00 ` [PATCH 1/1] vreportf(): avoid buffered write in favor of unbuffered one Johannes Schindelin via GitGitGadget
2019-10-29  3:18   ` Junio C Hamano
2019-10-29 12:30     ` Johannes Schindelin
2019-10-29 13:49       ` Jeff King
2019-10-29 14:13         ` Johannes Schindelin
2019-10-29 14:32           ` Jeff King
2019-10-29 20:09             ` Johannes Schindelin
2019-10-30  1:43               ` Junio C Hamano
2019-10-29 16:44         ` Junio C Hamano
2019-10-29 10:38   ` SZEDER Gábor
2019-10-29 12:38     ` Johannes Schindelin
2019-10-29 13:52       ` Jeff King
2019-10-29 14:18         ` Johannes Schindelin
2019-10-29 13:37 ` [PATCH v2 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget
2019-10-29 13:37   ` [PATCH v2 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget
2019-10-29 14:21     ` Alexandr Miloslavskiy
2019-10-29 19:57       ` Johannes Schindelin
2019-10-29 20:09         ` Jeff King
2019-10-29 20:24           ` Alexandr Miloslavskiy
2019-10-29 20:11         ` Alexandr Miloslavskiy
2019-10-29 20:01   ` [PATCH v3 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget
2019-10-29 20:01     ` [PATCH v3 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget
2019-10-29 20:32       ` Jeff King [this message]
2019-10-30  8:54         ` Johannes Schindelin
2019-10-31  6:24           ` Jeff King
2019-10-31 10:26             ` Johannes Schindelin
2019-10-31 15:48               ` Jeff King
2019-11-01 18:41                 ` Johannes Schindelin
2019-10-30  2:01       ` Junio C Hamano
2019-10-30  9:13         ` Johannes Schindelin
2019-10-30 10:44     ` [PATCH v4 0/1] Fix t5516 flakiness in Visual Studio builds Johannes Schindelin via GitGitGadget
2019-10-30 10:44       ` [PATCH v4 1/1] vreportf(): avoid relying on stdio buffering Johannes Schindelin via GitGitGadget
2019-11-02  4:05         ` Junio C Hamano

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