Re: [PATCH v7 2/4] KVM: stats: Add fd-based API to read binary stats data

Hi Paolo,

On Thu, Jun 10, 2021 at 11:42 AM Paolo Bonzini pbonzini@redhat.com wrote:

On 03/06/21 23:14, Jing Zhang wrote:

...

+struct _kvm_stats_header {

• __u32 name_size;
  

• __u32 count;
  

• __u32 desc_offset;
  

• __u32 data_offset;
  

+};

Keeping this struct in sync with kvm_stats_header is a bit messy. If you move the id at the end of the header, however, you can use the same trick with the zero-sized array that you used for _kvm_stats_desc.

Good point. Will do.

...

+struct kvm_vm_stats_data {

• unsigned long value[0];
  

+};

I posted the patch to switch the VM statistics to 64-bit; you can rebase on top of it.

Cool!

...

+#define KVM_GET_STATS_FD _IOR(KVMIO, 0xcc, struct kvm_stats_header)

This should be _IO(KVMIO, 0xcc) since it does not have an argument.

Will correct it.

...

+#define STATS_DESC(stat, type, unit, scale, exp) \

• {                                                                      \
  

•         {                                                              \
  

•                 .flags = type | unit | scale,                          \
  

•                 .exponent = exp,                                       \
  

•                 .size = 1                                              \
  

•         },                                                             \
  

•         .name = stat,                                                  \
  

Here you can use

    type | BUILD_BUG_ON_ZERO(type & ~KVM_STATS_TYPE_MASK) |
    unit | BUILD_BUG_ON_ZERO(unit & ~KVM_STATS_UNIT_MASK) |
    scale | BUILD_BUG_ON_ZERO(scale & ~KVM_STATS_SCALE_MASK) |

to get a little bit of type checking.

Sure, will do.

Paolo

Thanks, Jing