Re: [Qemu-devel] [PATCH v2 3/8] nvdimm acpi: introduce _FIT

[Xiao Guangrong]

On 10/11/2016 07:49 PM, Igor Mammedov wrote:
> On Mon, 10 Oct 2016 21:09:30 +0800
> Xiao Guangrong <address@hidden> wrote:
>
> > On 10/10/2016 08:51 PM, Igor Mammedov wrote:
> > > On Sat, 8 Oct 2016 15:17:14 +0800
> > > Xiao Guangrong <address@hidden> wrote:
> > >
> > > > On 09/30/2016 09:14 PM, Igor Mammedov wrote:
> > > > > On Fri, 12 Aug 2016 14:54:05 +0800
> > > > > Xiao Guangrong <address@hidden> wrote:
> > > > >
> > > > > > _FIT is required for hotplug support, guest will inquire the updated
> > > > > > device info from it if a hotplug event is received
> > > > > >
> > > > > > As FIT buffer is not completely mapped into guest address space, so a
> > > > > > new function, Read FIT whose function index is 0xFFFFFFFF, is reserved
> > > > > > by QEMU to read the piece of FIT buffer. The buffer is concatenated
> > > > > > before _FIT return
> > > > > Only issuer of UUID 2F10E7A4-9E91-11E4-89D3-123B93F75CBA can reserve
> > > > > 0xFFFFFFFF for some purposes.
> > > > > So spec should be amended first or custom generated UUID should be used.
> > > >
> > > > Okay.
> > > >
> > > > I will change the changelog to reflect this fact and move the spec update
> > > > to this patch.
> > > under spec, I've meant ACPI spec where this UUID is declared
> >
> > Er. ACPI spec just said that "0xFFFF is reserved", not sure it will be used
> > in the future.
> >
> > I'd prefer to custom-generated UUID, however, currently the UUID is checked
> > in OSPM, i.e, QEMU is not able to distinguish other UUIDs,
> I'd go with custom-generated UUID
>
> > so how about
> > drop the UUID check in ACPI and pass the UUID info to QEMU?
> It's a bit late to do so as it would be qemu-guest ABI change and
> one would need to maintain old and new protocol.

Okay.

How about extract 16 bits from 'handle' filed in NvdimmDsmIn buffer and use
it to indicate different UUIDs, i,e:
struct NvdimmDsmIn {
    uint16_t handle;
    uint16_t uuid_type;
    uint32_t revision;
    uint32_t function;
    /* the remaining size in the page is used by arg3. */
    union {
        uint8_t arg3[4084];
    };
} QEMU_PACKED;
typedef struct NvdimmDsmIn NvdimmDsmIn;

For this case, we set uuid_type = 1 to indicate the UUID is the one used
for RFIT.

u16 for 'handle' is large enough as QEMU supports 255 memory devices.