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



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.

>  /**
>   * 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

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/


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