Re: [KVM PATCH v7 3/3] kvm: add iofd support

Gregory Haskins
2009-05-14T12:02:39Z

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Avi Kivity wrote:
> Gregory Haskins wrote:
>> iofd is a mechanism to register PIO/MMIO regions to trigger an eventfd
>> signal when written to. Userspace can register any arbitrary address
>> with a corresponding eventfd.
>>
>>
>
> Please start a separate patchset for this so I can merge irqfd.

Ack. Will spin a new split series with your irqfd review changes
>
>>
>> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
>> index dfc4bcc..99b6e45 100644
>> --- a/include/linux/kvm.h
>> +++ b/include/linux/kvm.h
>> @@ -292,6 +292,17 @@ struct kvm_guest_debug {
>> struct kvm_guest_debug_arch arch;
>> };
>>
>> +#define KVM_IOFD_FLAG_DEASSIGN (1 << 0)
>> +#define KVM_IOFD_FLAG_PIO (1 << 1)
>> +
>> +struct kvm_iofd {
>> + __u64 addr;
>> + __u32 len;
>> + __u32 fd;
>> + __u32 flags;
>> + __u8 pad[12];
>> +};
>> +
>>
> Please add a data match capability. virtio uses a write with the data
> containing the queue ID, and we want a separate event for each queue.

How about "u64 cookie" ?
>
>
>> * kvm trace categories
>> @@ -508,6 +519,7 @@ struct kvm_irqfd {
>> #define KVM_DEASSIGN_DEV_IRQ _IOW(KVMIO, 0x75, struct
>> kvm_assigned_irq)
>> #define KVM_ASSIGN_IRQFD _IOW(KVMIO, 0x76, struct kvm_irqfd)
>> #define KVM_DEASSIGN_IRQFD _IOW(KVMIO, 0x77, __u32)
>> +#define KVM_IOFD _IOW(KVMIO, 0x78, struct kvm_iofd)
>>
>
> Too general a name. It's not doing IO, just sending out notifications.

Hmm...good point. I was trying to reflect "[MM/P]IO-FD". How about
"IOSIGNALFD"

>
> Why have assign/deassign for irqfd and a single ioctl for iofd?
Heh.. irqfd "liked" two because the deassign only needed a u32. iofd
needed more or less the same structure for both so I guess I thought I
would be "slick" and condense the vectors. Will fix so they are
symmetrical.

>
> The rest looks good.
>

I will also submit a patch to fix the io_bus stuff so that registrations
can gracefully fail instead of BUG_ON(), and to provide an unregister
function.

Thanks Avi,
-Greg

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