Re: [virtio-comment] [PATCH RFC] virtio: introduce VIRTIO_F_DEVICE_STOP

From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Halil Pasic <pasic@linux.ibm.com>,
	Cornelia Huck <cohuck@redhat.com>,
	stefanha@redhat.com, virtio-comment@lists.oasis-open.org,
	eperezma@redhat.com, sgarzare@redhat.com
Subject: Re: [virtio-comment] [PATCH RFC] virtio: introduce VIRTIO_F_DEVICE_STOP
Date: Mon, 28 Dec 2020 15:05:43 +0800	[thread overview]
Message-ID: <f15c2348-48e1-412f-4ef9-0f96b79a87d4@redhat.com> (raw)
In-Reply-To: <20201227061119-mutt-send-email-mst@kernel.org>

On 2020/12/27 下午7:12, Michael S. Tsirkin wrote:
> On Fri, Dec 25, 2020 at 02:45:28PM +0800, Jason Wang wrote:
>>> I tend to say, that from a perspective of the driver, all requests that
>>> are available, and not yet used, are in-flight. So we have to be very
>>> careful when wording this requirement, to avoid misunderstandings. I
>>> don't think the first RFC is good enough. I will think some more about
>>> this.
>>
>> Yes, I agree. The problem is that the spec doesn't describe how device work,
>> so if we want to be more accurate, it might require some work not only for
>> stop but also for e.g reset (something like in flight has been used by the
>> spec in that case).
> You probably mean the DEVICE_NEEDS_RESET description, right?
>
> 	For example, the driver can't assume requests in flight will be
> 	completed if DEVICE_NEEDS_RESET is set, nor can it assume that
> 	they have not been completed.  A good implementation will try to
> 	recover by issuing a reset.
>
> yes, DEVICE_NEEDS_RESET is unfortunately underspecified which likely
> is related to the fact it is not widely implemented.

For both NEEDS_RESET and device reset.

For NEEDS_RESET, we use "in flight" and "completed" without an actual 
definition.

For device reset, we don't even define what is the device expected (e.g 
how are "in flight" requests expected to be processed) to behave.

Thanks

>

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