"Daniel P. Berrange" <berrange@redhat.com> wrote:
On Fri, Aug 22, 2008 at 03:16:42PM +0200, Guido G?nther wrote:
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])
Hmm, I wonder if that's commonly installed by Fedora/Debian RPMs for KVM....
I've just checked up to date rawhide and debian unstable systems. Both had this: $ grep KVM_CHECK_EXTENSION /usr/include/linux/kvm.h #define KVM_CHECK_EXTENSION _IO(KVMIO, 0x03) But rawhide lacks KVM_CAP_NR_VCPUS, while Debian has it. $ grep -r KVM_CAP_NR_VCPUS /usr/include/linux/kvm.h #define KVM_CAP_NR_VCPUS 9 /* returns max vcpus per vm */
It might be neccessary to just #define the IOCTL constant in our own header files if its not available.
Good point. Otherwise, this patch looks fine.
@@ -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; +}
This is all very cool. IIRC Cole has some code which could guess a reasonable maxvcpus from KVM version number which we could potentially fallback to
Daniel