Re: [Updated PATCH 2/2] Improve transport helper exec failure reporting

From: Johannes Sixt <j6t@kdbg.org>
Date: Dec 31, 2009, 18:44 UTC
Message-ID: <4B3CF118.7080404@kdbg.org>
In-Reply-To: <20091231182436.GA1326@Knoppix>

Ilari Liusvaara schrieb:

Show 21 quoted lines

> On Thu, Dec 31, 2009 at 06:48:02PM +0100, Johannes Sixt wrote:
>> In case 3, it is expected that the child process prints a suitable
>> error message. Therefore, you should start with merely replacing the
>> unconditional
>>
>> 	exit(127);
>> by
>> 	if (errno == ENOENT)
>> 		exit(127);
>> 	else
>> 		die_errno("Cannot exec %s", cmd->argv[0]);
>>
>> And then you can think about how you support the ENOENT case better.
>> My proposal for this was to do the PATH lookup manually before the
>> fork(), and then the above conditional would melt down to simply:
>>
>> 	die_errno("Cannot exec %s", cmd->argv[0]);
>>
> 
> The child process can't sanely print anything. Stderr would go to
> who knows where.

Wrong - because:

> Parent process should have much better idea what to
> do with errors.

Very correct. For this reason, the parent process assigns a stderr channel to the child (or does not do so to inherit its own stderr), and the child is expected to use it. Errors due to execvp failures are no exception, IMO (except ENOENT, as always).

-- Hannes