Invalid arguments error when passing macros in c++ - c++

Question

There is a function like:
int kvm_vcpu_ioctl(int vcpu_fd,int type, ...)
{
int ret;
void *arg;
va_list ap;
va_start(ap, type);
arg = va_arg(ap, void *);
va_end(ap);
ret = ioctl(vcpu_fd, type, arg);
if (ret == -1)
ret = -errno;
return ret;
}
and when I want to call it but pass a macro as the argument like:
kvm_vcpu_ioctl(vcpus.fds[vcpu_id],KVM_NITRO_GET_SREGS,sregs);
in which defined macro is:
#define KVM_NITRO_GET_SREGS _IOR(KVMIO, 0xE9, struct kvm_sregs)
I get this error:
Invalid arguments '
Candidates are:
int kvm_vcpu_ioctl(int, int, ...)
I do not why?
_IOR is :
#define _IOR(type,nr,size) _IOC(_IOC_READ,(type),(nr),(_IOC_TYPECHECK(size)))
and _IOC is:
#define _IOC(dir,type,nr,size) \
(((dir) << _IOC_DIRSHIFT) | \
((type) << _IOC_TYPESHIFT) | \
((nr) << _IOC_NRSHIFT) | \
((size) << _IOC_SIZESHIFT))

Answer 1

Your definition of KVM_NITRO_GET_SREGS "calls" _IOR with a third argument of struct kvm_sregs. From the definition of _IOR, it would appear that perhaps a sizeof(struct kvm_sregs) might be more appropriate. Or perhaps you have arguments out of order, since it appears the first argument to _IOR should possibly be a type, but I'm not sure what KVMIO expands to...
Look for other locations where _IOR is used in other drivers, and mimic those.