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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

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

~Andrew

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