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

-----Original Message----- From: Jiri Denemark [mailto:jdenemar@redhat.com] Sent: Tuesday, November 24, 2015 12:25 AM To: Ren, Qiaowei Cc: libvir-list(a)redhat.com Subject: Re: [libvirt] [PATCH 3/8] perf: implement the public APIs for perf event 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(a)intel.com&gt; > --- > 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.