Re: [PATCH] Make EWOULDBLOCK be equal to EAGAIN on parisc.

[Guy Martin <gmsoft@tuxicoman.be>]

On 2014-01-16 22:15, Helge Deller wrote:
> On 01/16/2014 10:05 PM, Carlos O'Donell wrote:
>> On Thu, Jan 16, 2014 at 3:49 PM, John David Anglin 
>> <dave.anglin@bell.net> wrote:
>>>> This is an ABI break.
>>>> 
>>>> You can't do this without rebuilding userspace.
>>>> 
>>>> You need debian an gentoo onboard to do this ABI break.
>>> 
>>> This would take about a month on Debian, so I'm against.  Various 
>>> bits of kernel code traditionally
>>> return EWOULDBLOCK, so any application code that just checks 
>>> EWOULDBLOCK would fail.
>> 
>> That's not true if, like all other targets, EWOULDBLOCK == AGAIN. It's
>> only true on hppa, and that's the problem.
>> 
>> The kernel is completely inconsistent about returning EWOULDBLOCK or
>> EAGAIN, and the standards do dictate one or the other so the kernel
>> and glibc are correct to use one or the other to match the standard.
>> 
>> However, user applications are equally sloppy about checking the right 
>> value.
> 
> Guy, do you have actual programs which are currently broken and which
> don't check for both?
> My feeling is, that most programs were fixed, but I might be wrong...

As Mike pointed out, memcached had a test which failed only on hppa.
Fixing the test is easy but that lead me to check the code of 
libmemcache,
client counterpart of memcached. The same problem was there too. Only
EAGAIN was being checked.

I agree that this change will break the ABI. However it will only affect
applications checking solely for EWOULDBLOCK and not EAGAIN. I believe 
that
on linux, most if not all applications check for EAGAIN and few check 
for
EWOULDBLOCK as well.

The problem currently is that finding out which applications are not 
checking
for EWOULDBLOCK requires analyzing the code. Most of the time, failure 
to
correctly check for EWOULDBLOCK will be quite stealth depending on how 
the
application handles it.

So despite the fact that this will break the ABI, the breakage should be 
minimal
if non existent while it will fix a lot of hard to find and identify 
issues.

   Guy