On Wed, Jun 02, 2010 at 03:25:11PM +0300, Avi Kivity wrote: > On 06/02/2010 03:19 PM, Joerg Roedel wrote: >> >>> Yes. so you do: >>> iommu = open >>> ioctl(dev1, BIND, iommu) >>> ioctl(dev2, BIND, iommu) >>> ioctl(dev3, BIND, iommu) >>> ioctl(dev4, BIND, iommu) >>> >>> No need to add a SHARE ioctl. >>> >> In my proposal this looks like: >> >> >> dev1 = open(); >> ioctl(dev2, SHARE, dev1); >> ioctl(dev3, SHARE, dev1); >> ioctl(dev4, SHARE, dev1); >> >> So we actually save an ioctl. >> > > The problem with this is that it is assymetric, dev1 is treated > differently from dev[234]. It's an unintuitive API. Its by far more unintuitive that a process needs to explicitly bind a device to an iommu domain before it can do anything with it. If its required anyway the binding can happen implicitly. We could allow to do a nop 'ioctl(dev1, SHARE, dev1)' to remove the asymmetry. Note that this way of handling userspace iommu mappings is also a lot simpler for most use-cases outside of KVM. If a developer wants to write a userspace driver all it needs to do is: dev = open(); ioctl(dev, MAP, ...); /* use device with mappings */ close(dev); Which is much easier than the need to create a domain explicitly. Joerg -- 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
