Re: [Xen-devel] Returning errno values inside of hypercall structs (was: Re: [PATCH for-4.7 3/4] tools/xsplice: fix mixing system)

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Apr 29, 2016 at 07:07:44PM +0200, Roger Pau Monne wrote:
> On Fri, Apr 29, 2016 at 12:59:30PM -0400, Konrad Rzeszutek Wilk wrote:
> > > > > IMHO, the best way to solve this is to define a set of 
> > > > > XSPLICE_ERROR_* that 
> > > > > covers the error codes returned by xsplice, and use that instead of 
> > > > > XEN_* 
> > > > > errno values. This would make it much more easier to avoid mistakes 
> > > > > when 
> > > > > coding the toolstack part of xsplice.
> > > > 
> > > > But why?
> > > > 
> > > > I must be missing something here - but the return from the hypercall
> > > > can return say 0 but the status->rc can be -XEN_EAGAIN.
> > > > 
> > > > Why does it need to be XSPLICE_ERROR_?
> > > 
> > > Because nobody uses or enforces the correct usage of XEN_E* in the tools, 
> > > so 
> > > people just use native error codes, which works on Linux, but breaks on 
> > > other OSes.
> > 
> > That was an oversigh on my part. I think changing the error code handling
> > in xen-xsplice to look for XEN_EXX is the right way.
> > 
> > But are you saying the BSD does not enforce the POSIX errors? errno.h is 
> > POSIX right?
> 
> Yes, BSD uses POSIX error codes just as Linux, the issue is that the values 
> differ. For example on Xen and Linux EAGAIN is 11, on FreeBSD EAGAIN is 35.

Wow! That is messed up. And would explain the odd errors you had seen.

But if the xen-xsplice would use XEN_EXX error handling this would work for you 
right?
(Which BTW, thank you for doing!)

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