On 16.05.22 16:21, Pierre Morel wrote: > > > On 5/12/22 12:01, David Hildenbrand wrote: >>>> >>>> I think we prefer something like u16 when copying to user space. >>> >>> but then userspace also has to expect a u16, right? >> >> Yep. >> > > Yes but in fact, inspired by previous discussion I had on the VFIO > interface, that is the reason why I did prefer an int. > It is much simpler than a u16 and the definition of a bit. > > Despite a bit in a u16 is what the s3990 achitecture proposes I thought > we could make it easier on the KVM/QEMU interface. > > But if the discussion stops here, I will do as you both propose change > to u16 in KVM and userland and add the documentation for the interface. In general, we pass via the ABI fixed-sized values -- u8, u16, u32, u64 ... instead of int. Simply because sizeof(int) is in theory variable (e.g., 32bit vs 64bit). Take a look at arch/s390/include/uapi/asm/kvm.h and you won't find any usage of int or bool. Having that said, I'll let the maintainers decide. Using e.g., u8 is just the natural thing to do on a Linux ABI, but we don't really support 32 bit ... maybe we'll support 128bit at one point? ;) -- Thanks, David / dhildenb
