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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

> +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.

> +#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.

> +#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.

Paolo