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Re: [libvirt] [PATCHv2 1/6] virNodeGetCPUTime: Expose new API



Hi, Daniel.

Thank you for your review.

On Sun, 10 Apr 2011 12:58:56 +0800
Daniel Veillard <veillard redhat com> wrote:

> On Fri, Apr 08, 2011 at 08:33:12PM +0900, Minoru Usui wrote:
> > virNodeGetCPUTime: Expose new API
> > 
> > Signed-off-by: Minoru Usui <usui mxm nes nec co jp>
> > ---
> >  include/libvirt/libvirt.h.in |   64 ++++++++++++++++++++++++++++++++++++++++++
> >  src/libvirt_public.syms      |    5 +++
> >  2 files changed, 69 insertions(+), 0 deletions(-)
> > 
> > diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
> > index bd36015..154c138 100644
> > --- a/include/libvirt/libvirt.h.in
> > +++ b/include/libvirt/libvirt.h.in
> > @@ -228,6 +228,57 @@ struct _virNodeInfo {
> >      unsigned int threads;/* number of threads per core */
> >  };
> >  
> > +/**
> > + * virNodeCpuTime:
> > + *
> > + * a virNodeCpuTime is a structure filled by virNodeGetCpuTime() and providing
> > + * the information for the cpu time of the node.
> > + */
> > +
> > +/**
> > + * Cpu Time Statistics Tags:
> > + */
> > +typedef enum {
> > +    /*
> > +     * The cumulative CPU time which spends by kernel,
> > +     * when the node booting up.(in nanoseconds).
> > +     */
> > +    VIR_NODE_CPU_TIME_KERNEL               = 0,
> > +    /*
> > +     * The cumulative CPU time which spends by user processes,
> > +     * when the node booting up.(in nanoseconds).
> > +     */
> > +    VIR_NODE_CPU_TIME_USER                 = 1,
> > +    /*
> > +     * The cumulative idle CPU time,
> > +     * when the node booting up.(in nanoseconds).
> > +     */
> > +    VIR_NODE_CPU_TIME_IDLE                 = 2,
> > +    /*
> > +     * The cumulative I/O wait CPU time,
> > +     * when the node booting up.(in nanoseconds).
> > +     */
> > +    VIR_NODE_CPU_TIME_IOWAIT               = 3,
> > +    /*
> > +     * The CPU utilization.
> > +     * The usage value is in percent and 100% represents all CPUs on
> > +     * the server.
> > +     */
> > +    VIR_NODE_CPU_TIME_UTILIZATION          = 4,
> > +
> > +    /*
> > +     * The number of statistics supported by this version of the interface.
> > +     * To add new statistics, add them to the enum and increase this value.
> > +     */
> > +    VIR_NODE_CPU_TIME_NR                   = 5,
> > +} virNodeCpuTimeTags;
> > +
> > +typedef struct _virNodeCpuTime virNodeCpuTime;
> > +
> > +struct _virNodeCpuTime {
> > +    virNodeCpuTimeTags tag;
> > +    unsigned long long val;
> > +};
> 
>   NACK, the size of an enum is not defined by the C language and
> hence is compiler dependant. We cannot use it as a component of a
> structure in the API.

OK. I'll change the enum to int.
 
> >  /**
> >   * virDomainSchedParameterType:
> > @@ -460,6 +511,14 @@ int virDomainMigrateSetMaxSpeed(virDomainPtr domain,
> >  typedef virNodeInfo *virNodeInfoPtr;
> >  
> >  /**
> > + * virNodeCpuTimePtr:
> > + *
> > + * a virNodeCpuTimePtr is a pointer to a virNodeCpuTime structure.
> > + */
> > +
> > +typedef virNodeCpuTime *virNodeCpuTimePtr;
> > +
> > +/**
> >   * virConnectFlags
> >   *
> >   * Flags when opening a connection to a hypervisor
> > @@ -593,6 +652,11 @@ int                     virNodeGetInfo          (virConnectPtr conn,
> >                                                   virNodeInfoPtr info);
> >  char *                  virConnectGetCapabilities (virConnectPtr conn);
> >  
> > +int                     virNodeGetCpuTime       (virConnectPtr conn,
> > +                                                 virNodeCpuTimePtr stats,
> > +                                                 unsigned int nr_stats,
> > +                                                 unsigned int flags);
> > +
> 
>   I don't understand how the API is suppoed to work. Suppose you want
> the cumulative CPU time, how do you ask for it ? Seems you can't ! You
> just ask for a big stucture hoping that on return you may find it within
> the results. That looks broken to me.
> 
>   Either you make a simple API giving back an unsigned long long and
> you use the virNodeCpuTimeTags as the flag value
> 
>   int virNodeGetCpuTime(virConnectPtr conn, unsigned long long *time,
>                         unsigned int flags);
> 
> and the flags indicate the value you're interested into, but in that
> case you have to ask multiple times. Or you make the VIR_NODE_CPU_TIME_*
> values a bit field, and you pass an array
> 
>   int virNodeGetCpuTime(virConnectPtr conn,
>                         unsigned long long *stats,
>                         unsigned int nr_stats,
>                         unsigned int flags);
> 
> where flags is the logical or of the values you are interested into, and
> the implementation put them in order based on the VIR_NODE_CPU_TIME_*
> values. But in that case you must fail if one of the statistics is not
> available.
> 
>   But an API where you "go fishing" and you don't know upfront on a
> successful return if you got the data you're interested into sounds
> broken to me

Thank you for your useful advice.
I think the API user would be better to request which values return, too.

I'll change the I/F to above 2nd style.

> 
> Daniel
> 
> -- 
> Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
> daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
> http://veillard.com/ | virtualization library  http://libvirt.org/


-- 
Minoru Usui <usui mxm nes nec co jp>


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