[libvirt] [PATCH 3/8] perf: implement the public APIs for perf event

[Jiri Denemark]

On Tue, Nov 17, 2015 at 16:00:43 +0800, Qiaowei Ren wrote:
> * src/libvirt-domain.c: Implement virDomainGetPerfEvents and
> virDomainSetPerfEvents.
> 
> Signed-off-by: Qiaowei Ren <qiaowei.ren at intel.com>
> ---
>  src/libvirt-domain.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 106 insertions(+)
> 
> diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c
> index de7eb04..e767606 100644
> --- a/src/libvirt-domain.c
> +++ b/src/libvirt-domain.c
> @@ -9572,6 +9572,112 @@ virDomainOpenChannel(virDomainPtr dom,
>  
>  
>  /**
> + * virDomainGetPerfEvents:
> + * @domain: pointer to domain object
> + * @params: pointer to perf events parameter object
> + *          (return value, allocated by the caller)
> + * @nparams: pointer to number of perf event parameters
> + *
> + * Get all perf events setting. On input, @nparams gives the size of the
> + * @params array; on output, @nparams gives how many slots were filled
> + * with parameter information, which might be less but will not exceed
> + * the input value.
> + *
> + * As a special case, calling with @params as NULL and @nparams as 0 on
> + * input will cause @nparams on output to contain the number of parameters
> + * supported by the hypervisor. The caller should then allocate @params
> + * array, i.e. (sizeof(@virTypedParameter) * @nparams) bytes and call the
> + * API again.
> + *
> + * See virDomainGetMemoryParameters() for an equivalent usage example.

You took a wrong API to copy. Requiring the caller to run the API with
@params == NULL to get the number of parameters and then pass the
allocated @params to get the values is the original design which we do
not use for new APIs. The API should just allocate @params, fill it with
all the values it knows about, and return the count in @nparams. In
other words, no caller allocated arrays, please. You can look at, e.g.,
virDomainGetJobStats to see how it works.

Jirka