On 02/16/2012 03:04 AM, Michael Ellerman wrote: > > > > ioctl is good for hardware devices and stuff that you want to enumerate > > and/or control permissions on. For something like KVM that is really a > > core kernel service, a syscall makes much more sense. > > Yeah maybe. That distinction is at least in part just historical. > > The first problem I see with using a syscall is that you don't need one > syscall for KVM, you need ~90. OK so you wouldn't do that, you'd use a > multiplexed syscall like epoll_ctl() - or probably several > (vm/vcpu/etc). No. Many of our ioctls are for state save/restore - we reduce that to two. Many others are due to the with/without irqchip support - we slash that as well. The device assignment stuff is relegated to vfio. I still have to draw up a concrete proposal, but I think we'll end up with 10-15. > > Secondly you still need a handle/context for those syscalls, and I think > the most sane thing to use for that is an fd. The context is the process (for vm-wide calls) and thread (for vcpu local calls). > > At that point you've basically reinvented ioctl :) > > I also think it is an advantage that you have a node in /dev for > permissions. I know other "core kernel" interfaces don't use a /dev > node, but arguably that is their loss. Have to agree with that. Theoretically we don't need permissions for /dev/kvm, but in practice we do. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
