Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [kvm-devel] [PATCH 3/3] KVM: Expose MSRs to userspace | Date | Thu, 16 Nov 2006 20:08:48 +0100 |
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On Thursday 16 November 2006 19:04, Avi Kivity wrote: > +struct kvm_msr_entry { > + __u32 index; > + __u32 reserved; > + __u64 data; > +}; > + > +/* for KVM_GET_MSRS and KVM_SET_MSRS */ > +struct kvm_msrs { > + __u32 vcpu; > + __u32 nmsrs; /* number of msrs in entries */ > + > + union { > + struct kvm_msr_entry __user *entries; > + __u64 padding; > + }; > +};
ioctl interfaces with pointers in them are generally a bad idea, though you handle most of the points against them fine here (endianess doesn't matter, padding is correct).
Still, it might be better not to set a bad example. Is accessing the MSRs actually performance critical? If not, you could define the ioctl to take only a single entry argument.
A possible alternative could also be to have a variable length argument like below, but that creates other problems:
+struct kvm_msrs { + __u32 vcpu; + __u32 nmsrs; /* number of msrs in entries */ + struct kvm_msr_entry entries[0]; /* followed by actual msrs */ +};
This would mean that you can't tell the transfer size from the ioctl number, but you can't do that in your code either, because you do two separate transfers.
Arnd <>< - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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