Re: [PATCH v5 3/8] convert: Split start_multi_file_filter into two separate functions

[Lars Schneider <larsxschneider@gmail.com>]

> On 11 Apr 2017, at 21:37, Jeff King <peff@peff.net> wrote:
> 
> On Tue, Apr 11, 2017 at 09:29:36PM +0200, Lars Schneider wrote:
> 
>>> 1. Do we need to save errno before calling sigchain_pop()? It's making
>>>    syscalls (though admittedly they are unlikely to fail).
>> 
>> What if we add the following right before sigchain_pop() ?
>> 
>> 	if (errno == EPIPE)
>> 		err = -1;
> 
> Yes, that would be fine (though again, this runs against point 2 below).
> 
>>> 2. If err is 0, then nothing failed. Who would have set errno? Aren't
>>>    we reading whatever cruft happened to be in errno before the
>>>    function started?
>> 
>> Yeah, looks like you're right:
>> https://www.securecoding.cert.org/confluence/pages/viewpage.action?pageId=6619179
>> 
>> According to this article we shouldn't even check *only* for errno. 
>> At least we should add
>> 	errno = 0;
>> at the beginning of the function, no?
> 
> If you initialize errno to 0 right before a syscall, then yes, you can
> trust it without checking the return value of the syscall. I wouldn't
> trust it before calling more complicated functions, though. Not even
> xwrite(), which may see EINTR and keep going (which is OK for checking
> for EPIPE, but not checking generally for errno values).

Should we remove all the errno checks here as we don't have any direct 
"write" etc syscalls anyways then?


- Lars