Re: POSIX error names and codes in PV protocols

[Julien Grall <julien.grall@arm.com>]

Hi,

On 26/01/2017 17:28, Oleksandr Andrushchenko wrote:
> On 01/26/2017 05:44 PM, Jan Beulich wrote:
>>>>> On 26.01.17 at 15:40, <andr2000@gmail.com> wrote:
>>> There is some work happening on new PV protocols: sndif [1],
>>>
>>> displif [2], PV calls [3] and the common part of those is that
>>>
>>> error/status codes must be returned as a part of a response packet.
>>>
>>> For that Konrad suggested [1] (and Stefano already used in [3]) POSIX
>>>
>>> to be employed here instead of defining protocol specific error codes.
>>>
>>> The problem I see here is that POSIX only defines names of the errors,
>>>
>>> but not values [4]. So, in order to use POSIX one still needs to define
>>>
>>> the values (names must be the same, but values may differ for different
>>> OSes).
>>>
>>> So, the question is what would be the best option to
>>>
>>> a) have those numbers defined in OS agnostic way
>>>
>>> b) have those defined for all PV protocols
>>>
>>> Stefano has already defined the error code values in his work [3],
>>>
>>> but for other protocols this should be reimplemented again.
>> Aren't these simply what public/errno.h provides? Why would any
>> Xen specific protocol want to define their own, now that we have
>> this base set?
>>
>> Jan
> Indeed, thank you
> The problem is that it is not exposed to Linux, but I can see it
> in FreeBSD [1] and the helper to convert error codes [2] there as well.
> Is there any reason these are not available in Linux?

This is because Linux and Xen are using the exact same error codes. The 
one in FreeBSD differs a bit, hence the helper to convert errors.

Strictly speaking Linux should have a converter, but it is not necessary 
today.

Cheers,

-- 
Julien Grall

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