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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Jan 26, 2017 at 08:14:10PM +0200, Oleksandr Andrushchenko wrote:
> On 01/26/2017 07:38 PM, Roger Pau Monné wrote:
> > On Thu, Jan 26, 2017 at 07:28:44PM +0200, Oleksandr Andrushchenko wrote:
> > > 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?
> > Xen error codes are Linux error codes, so I guess there's basically no need 
> > to
> > use them on Linux (although it would be good, just so that people is aware 
> > that
> > Xen and Linux are in different theoretical spaces, which happen to match in
> > Linux's case).
> > 
> > Roger.
> Thank you for clarifications.
> Does it mean that I can state in PV protocols that XEN_E??? error codes are
> used and still use Linux error codes directly in Linux front/back w/o
> complains
> from the community because of no conversion? :)

I guess if it's inside of the Linux kernel that's fine (although that's a
question for the Linux maintainers). If it runs in user-space you certainly
need to use the XEN_E error codes.

Roger.

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