Re: [libvirt] [PATCH] kvm: maxVCPU runtime detection

Hi, with recent linux kernels we can detect the maximum number of virtual cpus at runtime via an ioctl. Possible patch attached. It does this on every call to qemudGetMaxVCPUs. Would you prefer something that does this only once in qemudStartup()? Cheers, -- Guido

+dnl +dnl check for kvm headers +dnl +AC_CHECK_HEADERS([linux/kvm.h])

@@ -72,6 +77,9 @@ static int qemudShutdown(void); #endif +/* device for kvm ioctls */ +#define KVM_DEVICE "/dev/kvm" + /* qemudDebug statements should be changed to use this macro instead. */ #define DEBUG(fmt,...) VIR_DEBUG(__FILE__, fmt, __VA_ARGS__) #define DEBUG0(msg) VIR_DEBUG(__FILE__, "%s", msg) @@ -1768,6 +1776,29 @@ static const char *qemudGetType(virConnectPtr conn ATTRIBUTE_UNUSED) { return "QEMU"; } + +static int kvmGetMaxVCPUs(void) { + int maxvcpus = 1; + +#if defined(KVM_CAP_NR_VCPUS) + int r, fd; + + fd = open(KVM_DEVICE, O_RDONLY); + if (fd < 0) { + qemudLog(QEMUD_WARN, _("Unable to open " KVM_DEVICE ": %s\n"), strerror(errno)); + return maxvcpus; + } + + r = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS); + if (r > 0) + maxvcpus = r; + + close(fd); +#endif + return maxvcpus; +}