On Sat, May 11, 2013 at 1:04 AM, Peter Maydell <peter.maydell@xxxxxxxxxx> wrote: > On 11 May 2013 01:38, Christoffer Dall <cdall@xxxxxxxxxxxxxxx> wrote: >> On Tue, May 07, 2013 at 05:36:52PM +0100, Marc Zyngier wrote: >>> Here's what the documentation says: >>> <quote> >>> 4.77 KVM_ARM_VCPU_INIT >>> >>> Capability: basic >>> Architectures: arm, arm64 >>> Type: vcpu ioctl >>> Parameters: struct struct kvm_vcpu_init (in) >>> Returns: 0 on success; -1 on error >>> Errors: >>> EINVAL: the target is unknown, or the combination of features is invalid. >>> ENOENT: a features bit specified is unknown. >>> </quote> >>> >>> When this call fails, it is because you've requested a feature >>> that is invalid for this CPU. To me, that exactly fits the >>> EINVAL entry copied above. >>> >>> Or am I completely misunderstanding it? >>> >> I read the EINVAL to say that you supplied something which is invalid >> for the software interface and you should fix your user space code. > > Well, more likely "tell the user they picked a bad feature combo"; > I doubt userspace is going to bother specifically trying to track > which features don't go together when we can get a reliable answer > just by asking the kernel. > >> The fact that you're requesting a feature that your hardware doesn't >> support is a different thing IMHO. > > My reading of the docs above would be that "ENOENT" is "I have > no idea what feature you just asked me for" and "EINVAL" is > "I know those features but can't do them". That said, we don't > actually do anything with the error return yet so we should > feel free to clarify things so that it's clear what error is > returned for the cases we care about distinguishing. It seems > like it would be useful to have separate errors for: > * the kernel doesn't support this CPU > * the kernel doesn't support this feature bit > * the combination of CPU and features doesn't make sense > > and at the moment we've shoehorned two of those into one > errno, hence the confusion. > > (do we need to distinguish "I know about but don't support X" > from "I have no idea what you mean when you say X" ?) > I just think that saying "EINVAL: Invalid argument" for a perfectly valid argument which is just not supported on this hardware is what's wrong, I think ENXIO or ENODEV or whatever is more appropriate of this. -Christoffer -- 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
