[RFC v3 05/10] KVM: selftests: Print the vcpu_id when KVM_CREATE_VCPU ioctl fails

[Ritesh Harjani (IBM)]

Print the vcpu_id and errno when the KVM_CREATE_VCPU ioctl fails, for
debug purposes.
This helped in debugging an issue with KVM on PowerVM, where KVM_CREATE_VCPU
only supports max 2048 vcpus, because the PAPR_HCALL H_GUEST_CREATE_VCPU
("Documentation/arch/powerpc/kvm-nested.rst") supports only up to 0-2047
vcpu_id. However KVM_CAP_MAX_VCPUS capability extension always reports max_vcpus
as NR_CPUS of the host.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
---
 tools/testing/selftests/kvm/lib/kvm_util.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index e00a25f59416..6319e2037882 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1354,6 +1354,13 @@ struct kvm_vcpu *__vm_vcpu_add(struct kvm_vm *vm, u32 vcpu_id)
 	vcpu->vm = vm;
 	vcpu->id = vcpu_id;
 	vcpu->fd = __vm_ioctl(vm, KVM_CREATE_VCPU, (void *)(unsigned long)vcpu_id);
+	if (vcpu->fd < 0) {
+		int saved_errno = errno;
+
+		pr_info("Failed KVM_CREATE_VCPU for vcpu_id %u with errno %d\n",
+			vcpu_id, saved_errno);
+		errno = saved_errno;
+	}
 	TEST_ASSERT_VM_VCPU_IOCTL(vcpu->fd >= 0, KVM_CREATE_VCPU, vcpu->fd, vm);
 
 	TEST_ASSERT(vcpu_mmap_sz() >= sizeof(*vcpu->run), "vcpu mmap size "
-- 
2.39.5