Proposal : add 3 functions to Libvirt API, for virtual CPUs

[michel.ponceau@xxxxxxxx]

For our administration, we need the following actions, while concerned domain is running:
1) Change the number of virtual CPUs.
2) Change the pinning (affinity) of a virtual CPU on real CPUs.
3) Get detailed information for each virtual CPU.
Currently there is no Libvirt function provided for that. We suggest to add the following 3 functions (in libvirt.c):
/**
 * virDomainSetVcpus:
 * @domain: pointer to domain object, or NULL for Domain0
 * @nvcpus: the new number of virtual CPUs for this domain
 *
 * Dynamically change the number of virtual CPUs used by the domain.
 * Note that this call may fail if the underlying virtualization hypervisor
 * does not support it or if growing the number is arbitrary limited.
 * This function requires priviledged access to the hypervisor.
 *
 * Returns 0 in case of success, -1 in case of failure.
 */
int virDomainSetVcpus(virDomainPtr domain, unsigned int nvcpus)

/**
 * virDomainPinVcpu:
 * @domain: pointer to domain object, or NULL for Domain0
 * @vcpu: virtual CPU number
 * @cpumap: pointer to a bit map of real CPUs (format in virVcpuInfo)
 * @maplen: length of cpumap, in 8-bit bytes
 * 
 * Dynamically change the real CPUs which can be allocated to a virtual CPU.
 * This function requires priviledged access to the hypervisor.
 *
 * Returns 0 in case of success, -1 in case of failure.
 */
int virDomainPinVcpu(virDomainPtr domain, unsigned int vcpu,
                 unsigned char *cpumap, int maplen)

/**
 * virDomainGetVcpus:
 * @domain: pointer to domain object, or NULL for Domain0
 * @info: pointer to an array of virVcpuInfo structures
 * @maxinfo: number of structures in info array
 * 
 * Extract information about virtual CPUs of a domain, store it in info array.
 *
 * Returns the number of info filled in case of success, -1 in case of failure.
 */
int virDomainGetVcpus(virDomainPtr domain, virVcpuInfoPtr info, int maxinfo)

with the following structure (in libvirt.h):
/**
 * virVcpuInfo: structure for information about a virtual CPU in a domain.
 */
#define VIR_MAX_CPUS                256
typedef enum {
    VIR_VCPU_OFFLINE        = 0,        /* the virtual CPU is offline */
    VIR_VCPU_RUNNING        = 1,        /* the virtual CPU is running */
    VIR_VCPU_BLOCKED        = 2,        /* the virtual CPU is blocked on resource */
} virVcpuState;

typedef struct _virVcpuInfo virVcpuInfo;
struct _virVcpuInfo {
    unsigned int number;        /* virtual CPU number */
    int state;                        /* value from virVcpuState */
    unsigned long long cpuTime; /* CPU time used, in nanoseconds */
    int cpu;                        /* real CPU number, or -1 if offline */
    unsigned char cpumap[VIR_MAX_CPUS/8]; /* Bit map of usable real CPUs.
                Each bit set to 1 means that corresponding CPU is usable.
                Bytes are stored in little-endian order: CPU0-7, 8-15...
                In each byte, lowest CPU number is least significant bit */
};
typedef virVcpuInfo *virVcpuInfoPtr;

I have successfully tried those functions via Xen hypervisor, except for the first (SetVcpus) where hypervisor operation DOM0_MAX_VCPUS fails (maybe it is not possible on a running domain ?). That function was successful via Xen daemon.