Re: [Xen-devel] [PATCH v2 4/5] x86/hvm: Add debug exception vm_events

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.05.16 at 17:35, <tamas@xxxxxxxxxxxxx> wrote:
> On May 2, 2016 07:12, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>>
>> >>> On 29.04.16 at 20:07, <tamas@xxxxxxxxxxxxx> wrote:
>> > @@ -229,8 +231,15 @@ struct vm_event_write_ctrlreg {
>> >      uint64_t old_value;
>> >  };
>> >
>> > +struct vm_event_singlestep {
>> > +    uint64_t gfn;
>> > +};
>> > +
>> >  struct vm_event_debug {
>> >      uint64_t gfn;
>> > +    uint8_t type;        /* HVMOP_TRAP_* */
>> > +    uint8_t insn_length;
>> > +    uint8_t _pad[6];
>> >  };
>>
>> This being an incompatible change - didn't you mean to increment some
>> version number?
> 
> I'm not sure. It would still work with clients compiled with the older
> version of the header as the layout of the debug struct didnt change, was
> just appended. The size of the request/response struct didn't change either
> so technically this would still be backwards compatible.

But you also need to consider the other direction: Code compiled
against the new variant, but running on an older hypervisor would
expect the new fields to be valid, yet they can't be, and the caller
has no way to know.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel