On Mon, Nov 17, 2014 at 5:37 PM, Jan Beulich <jbeul...@suse.com> wrote:
> >>> On 12.11.14 at 16:48, <andrew.coop...@citrix.com> wrote: > > On 12/11/14 15:31, Tamas K Lengyel wrote: > >> xen/include/public/domctl.h | 44 +-- > >> xen/include/public/hvm/params.h | 2 +- > >> xen/include/public/mem_event.h | 134 ------- > >> xen/include/public/memory.h | 6 +- > >> xen/include/public/vm_event.h | 179 +++++++++ > > > > While in principle I think this series is a very good thing, there is a > > problem with editing the pubic header files. > > > > The contents of mem_event.h is not currently hidden behind #ifdef > > __XEN_TOOLS__ > > > > As a result, it is strictly speaking part of the VM-visible public > > API/ABI and not permitted to change in a backwards incompatible manor. > > > > Having said that, it is currently only usable by privileged domains, so > > there is an argument to be made for declaring that it should have been > > hidden behind __XEN_TOOLS__ in the first place, making it permittable to > > change. > > I'm not sure I agree - the meaning of "tools" here would seem quite a > bit different than e.g. in domctl.h. Looking at patch 1, I can't see how > an old consumer (remember that for many of these we have at best > fake consumers in the tree) would deal with the now differently > arranged data. I don't see any versioning of the interface, and hence > I can't see how tools would know which of the formats to expect. > > Jan > The lack of versioning is a real concern which I have aired during the 4.5 development process. For example, when we switched from HVMEM_access_* to XENMEM_access_* a customer had to do a bunch of manual configure checks to determine what is supported and what isn't. Furthermore, many of the related APIs have changed quite radically between Xen 4.1-4.5, some being abandoned midway just to resurface later in a different context. Going forward having a clear VM_EVENT_VERSION definition would be very helpful and would be the cleanest solution IMHO. Tamas
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