Re: [PATCH for-4.15] dmop: Add XEN_DMOP_nr_vcpus

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Andrew Cooper writes ("[PATCH for-4.15] dmop: Add XEN_DMOP_nr_vcpus"):
> Curiously absent from the stable API/ABIs is an ability to query the number of
> vcpus which a domain has.  Emulators need to know this information in
> particular to know how many stuct ioreq's live in the ioreq server mappings.
> 
> In practice, this forces all userspace to link against libxenctrl to use
> xc_domain_getinfo(), which rather defeats the purpose of the stable libraries.

Wat

> For 4.15.  This was a surprise discovery in the massive ABI untangling effort
> I'm currently doing for XenServer's new build system.

Given that this is a new feature at a late stage I am going to say
this:

I will R-A it subject to it getting *two* independent Reviewed-by.

I will try to one of them myself :-).

...

> +/*
> + * XEN_DMOP_nr_vcpus: Query the number of vCPUs a domain has.
> + *
> + * The number of vcpus a domain has is fixed from creation time.  This bound
> + * is applicable to e.g. the vcpuid parameter of XEN_DMOP_inject_event, or
> + * number of struct ioreq objects mapped via XENMEM_acquire_resource.

AIUI from the code, the value is the maximum number of vcpus, in the
sense that they are not necessarily all online.  In which case I think
maybe you want to mention that here ?

> diff --git a/xen/include/xlat.lst b/xen/include/xlat.lst
> index 398993d5f4..cbbd20c958 100644
> --- a/xen/include/xlat.lst
> +++ b/xen/include/xlat.lst
> @@ -107,6 +107,7 @@
>  ?    dm_op_set_pci_intx_level        hvm/dm_op.h
>  ?    dm_op_set_pci_link_route        hvm/dm_op.h
>  ?    dm_op_track_dirty_vram          hvm/dm_op.h
> +?    dm_op_nr_vcpus                  hvm/dm_op.h
>  !    hvm_altp2m_set_mem_access_multi hvm/hvm_op.h
>  ?    vcpu_hvm_context                hvm/hvm_vcpu.h
>  ?    vcpu_hvm_x86_32                 hvm/hvm_vcpu.h
> -- 

I have no idea what even.  I read the comment at the top of the file.

So for *everything except the xlat.lst change*
Reviewed-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>

Thanks,
Ian.