linux-kernel - Re: [PATCH 0/2] 9p/trans_virtio: handle request cancellation

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Date:   Mon, 8 Jan 2018 10:18:09 +0100
From:   Greg Kurz <groug@...d.org>
To:     linux-kernel@...r.kernel.org
Cc:     v9fs-developer@...ts.sourceforge.net,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 0/2] 9p/trans_virtio: handle request cancellation

Hi Michael,

I wish you a happy new year, and I really need some feedback on this
series because it holds down some patches on the QEMU side.

Thanks,

--
Greg

On Wed, 20 Dec 2017 18:46:27 +0100
Greg Kurz <groug@...d.org> wrote:

> The 9p protocol mostly relies on a request/reply dialog between the
> client and the server. A notable exception to this rule is request
> cancellation (ie, flush in 9p wording): when the client requests an
> in-flight request to be flushed, the server should only reply to the
> flush request and not to the flushed in-flight request (otherwise it
> considers the in-flight request to have completed just like it has
> never been flushed).
> 
> It is up to the client to inform the transport that the in-flight request
> has been flushed and won't receive a reply. This is achieved with the
> 'cancelled' operation of the struct p9_trans_module.
> 
> This operation isn't currently implemented with the virtio transport.
> As a consequence, flushed requests leave buffers in the used list
> forever and the virtqueue ends up in being able to process only one
> request at a time.
> 
> This issue never popped up because the 9p server in QEMU had a bug
> and would always reply to flushed requests. But this will be fixed
> soon, so it is time to implement the 'cancelled' operation in the
> 9p virtio transport.
> 
> --
> Greg
> 
> ---
> 
> Greg Kurz (2):
>       virtio: allow to detach a buffer from the virtqueue
>       9p/trans_virtio: implement cancelled callback
> 
> 
>  drivers/virtio/virtio_ring.c |   28 ++++++++++++++++++++++++++++
>  include/linux/virtio.h       |    1 +
>  net/9p/trans_virtio.c        |   18 ++++++++++++++++++
>  3 files changed, 47 insertions(+)
> 
>