Re: [Xen-devel] [RFC Patch v4 7/9] correct xc_domain_save()'s return value

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-09-22 at 14:03 +0100, Ian Jackson wrote:
> Ian Campbell writes ("Re: [Xen-devel] [RFC Patch v4 7/9] correct 
> xc_domain_save()'s return value"):
> > libxc doesn't know that, if it is important then it seems like the
> > failure + errno ought to be marshalled across the IPC link.
> 
> Yes, but ...
> 
> > It may be that this can be easily handled in
> > libxl__srm_callout_sendreply + helper_getreply. Ian J -- what do you
> > think?
> 
> ... while that would be possbile, we have another option.
> 
> We could say that the callbacks return errno values.  That would
> simplify the API and avoid having the IPC involve accesses to global
> variables (ie, things not in the functions' parameter lists).
> 
> If we do that then it becomes the responsibility of xc_domain_save to
> either change its own API to return errno, or to save the callback's
> return value in errno.

Hrm. libxc is already a complete mess wrt error returning/handling
because some proportion of the code incorrectly does/assumes this sort
of thing is happening (because people were confused about the syscall
returns from the kernel vs. process context). Having a place in libxc
where this is now done on purpose seems a bit like setting the rope on
fire to me...

Ian.



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