Re: [Xen-devel] POSIX error names and codes in PV protocols

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

On 01/26/2017 05:44 PM, Jan Beulich wrote:
> > > > On 26.01.17 at 15:40, <andr2000@xxxxxxxxx> 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?

Besides this fact,
Konrad, Stefano, are you ok that we say in the protocol file that
these are the error codes used?
As error codes are unsigned ints, what should be used in packets?
uint16_t or uint32_t?

Thank you,
Oleksandr

[1] https://github.com/freebsd/freebsd/blob/master/sys/xen/interface/errno.h
[2] https://github.com/freebsd/freebsd/blob/master/sys/xen/error.h


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