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qemu: Fix retrieval of maximum number of vCPUs on KVM hosts

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The detection of the maximum number of cpus used incorrect ioctl
argument value. This flaw caused that on kvm hosts this returns always
"160" as the maximum. This is just a recommended maximum value. The real
value is higher than that.

This patch tweaks the detection function to behave as described by the
kernel docs:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/virtual/kvm/api.txt?id=refs/tags/v3.9-rc2#n199
This commit is contained in:
Peter Krempa 2013-03-11 14:50:54 +01:00
parent 5c86ace1e7
commit 1715c83b5f
1 changed files with 19 additions and 10 deletions
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29
src/qemu/qemu_driver.c
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@ -1103,23 +1103,32 @@ static int qemuIsAlive(virConnectPtr conn ATTRIBUTE_UNUSED)
} }
static int kvmGetMaxVCPUs(void) { static int
int maxvcpus = 1; kvmGetMaxVCPUs(void) {
int fd;
int ret;
int r, fd; if ((fd = open(KVM_DEVICE, O_RDONLY)) < 0) {
fd = open(KVM_DEVICE, O_RDONLY);
if (fd < 0) {
virReportSystemError(errno, _("Unable to open %s"), KVM_DEVICE); virReportSystemError(errno, _("Unable to open %s"), KVM_DEVICE);
return -1; return -1;
} }
r = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS); /* at first try KVM_CAP_MAX_VCPUS to determine the maximum count */
if (r > 0) if ((ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_MAX_VCPUS)) > 0)
maxvcpus = r; goto cleanup;
/* as a fallback get KVM_CAP_NR_VCPUS (the recommended maximum number of
* vcpus). Note that on most machines this is set to 160. */
if ((ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS)) > 0)
goto cleanup;
/* if KVM_CAP_NR_VCPUS doesn't exist either, kernel documentation states
* that 4 should be used as the maximum number of cpus */
ret = 4;
cleanup:
VIR_FORCE_CLOSE(fd); VIR_FORCE_CLOSE(fd);
return maxvcpus; return ret;
} }