Re: [Xen-devel] [PATCH] tools/libxc: Fix domid parameter types

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Oct 09, 2017 at 03:51:49PM +0100, Andrew Cooper wrote:
> On 09/10/17 15:47, Wei Liu wrote:
> > On Fri, Oct 06, 2017 at 08:00:00PM +0100, Andrew Cooper wrote:
> >> Mixed throughout libxc are uint32_t, int, and domid_t for domid parameters.
> >> With a signed type, and an explicitly 16-bit type, it is exceedingly 
> >> difficult
> >> to construct an INVALID_DOMID constant which works with all of them.  (The
> >> main problem being that domid_t gets unconditionally zero extended when
> >> promoted to int for arithmatic.)
> >>
> >> Libxl uses uint32_t consistently everywhere, so alter libxc to match.
> > I would rather using domid_t throughout in libxc. Is there any problem
> > with that?
> 
> That would cause implicit truncation between libxl's idea of a domid,
> and libxc's idea of a domid.  In practice, it means any libxl domid with
> the upper 16 bits set may start to work (on the wrong domain!) where
> they may have failed previously.
> 

But that's already the case for a lot of hypercalls -- domid_t is widely
used in public headers. The truncation happens regardless of what libxc
uses.

> Finally, it won't fix the INVALID_DOMID constant problem, as xc_dom.h
> leaks fully into libxl.
> 

Sorry, I don't follow. What do you want to do?

Surely INVALID_DOMID should be part of public ABI? How does something in
xc_dom.h leaking (what is leaking?) change that?

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