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Re: [RFC 0/2] virtio-rng: add a control queue

From: Laurent Vivier
Subject: Re: [RFC 0/2] virtio-rng: add a control queue
Date: Fri, 24 Jan 2020 14:50:22 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2

On 24/01/2020 13:43, Amit Shah wrote:
> On Thu, 2020-01-23 at 16:16 +0100, Laurent Vivier wrote:
>> The kernel needs sometime to be able to cancel an ongoing command.
>> For instance, if the virtio-rng device uses the egd backend
>> and this backend doesn't provide data, the buffer provided by the
>> kernel is kept as long as it is needed.
>> On the kernel side, a read blocks until the buffer returns from QEMU.
>> As the read is done with a mutex held, all the hw_random interface
>> hangs and we cannot switch to another hw_random backend.
>> So this series adds a control queue to the virtio-rng device to allow
>> to flush the virtio-rng input queue to release the kernel mutex and
>> to allow to switch to another device.
>> The kernel side series can be found at:
>> https://github.com/vivier/linux/commits/virtio-rng-ctrl
> Did you submit the kernel series too?  Can you please CC me to it?

No, I didn't. I'd like to have some comments on the QEMU side first.
QEMU list is generally more responsive than kernel one.

It's why I put the link to my linux branch here.

> This will need spec changes as well, can you please point me to them
> too?

The same here. I didn't update the specs, I'd like to have some comments

BTW, where can I find the specs to update?
Is this https://github.com/oasis-tcs/virtio-spec ?

> I also recall a previous discussion about this, but my search-fu is
> failing to find it...


[RFC] virtio-rng: add a watchdog


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