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From: Jonathan Nieder <jrnieder@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, Jeff King <peff@peff.net>
Subject: Re: [REGRESSION] git-wrapper to run-commands codepath regression
Date: Mon, 18 Apr 2011 17:17:20 -0500	[thread overview]
Message-ID: <20110418221720.GA16977@elie> (raw)
In-Reply-To: <7v4o5v8dlp.fsf@alter.siamese.dyndns.org>

Junio C Hamano wrote:

>     	if (write(...))
>     		; /* yes, yes, there was an error. */
>
> No, a non-zero return is not an error from the write(2) system call.
> I cannot believe both of us didn't spot it.  What were we smoking?

Yagh.

	if (write(child_err, "fatal: ", 7) ||
	    write(child_err, msg, len) ||
	    write(child_err, "\n", 1))
		; /* yes, gcc -D_FORTIFY_SOURCE, we know there was an error. */

There are two unusual conditions in which this could fail:

 - it doesn't write anything at all, in which case the return value
   is -1.
 - a partial write, for example if writing to an almost-full pipe.

I suppose in a calmer time, a better fix will look like

	if (write_in_full(child_err, "fatal: ", 7) != 7 ||
	    write_in_full(child_err, msg, len) != len ||
	    write_in_full(child_err, "\n", 1) != 1)
		/* yes, yes, ...

and gcc will have told us something potentially useful.

Thanks for catching it.

  reply	other threads:[~2011-04-18 22:17 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-18 20:54 [REGRESSION] git-wrapper to run-commands codepath regression Junio C Hamano
2011-04-18 21:11 ` Jeff King
2011-04-18 21:18   ` Jeff King
2011-04-18 21:40     ` Junio C Hamano
2011-04-18 21:43       ` Jeff King
2011-04-18 22:10         ` Junio C Hamano
2011-04-18 22:11       ` Andreas Schwab
2011-04-18 21:16 ` Junio C Hamano
2011-04-18 22:17   ` Jonathan Nieder [this message]
2011-04-19  7:05   ` [PATCH] run-command: write full error message in die_child Jonathan Nieder
2011-04-20  7:42     ` Johannes Sixt
2011-04-20 10:33       ` [PATCH v2 0/2] " Jonathan Nieder
2011-04-20 10:35         ` [PATCH 1/2] tests: check error message from run_command Jonathan Nieder
2011-04-20 10:40         ` [PATCH 2/2] run-command: handle short writes and EINTR in die_child Jonathan Nieder
2011-04-19  0:07 ` [REGRESSION] git-wrapper to run-commands codepath regression Junio C Hamano
2011-04-20  4:01   ` [PATCH] report which $PATH entry had trouble running execvp(3) Junio C Hamano
2011-04-20  5:51     ` Jeff King
2011-04-21  0:00       ` Junio C Hamano
2011-04-20  7:37     ` Johannes Sixt
2011-04-20 11:21     ` Jonathan Nieder

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