linux-kernel - Re: [PATCH 1/3] virtio: add virtioqueue_more

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Date:   Tue, 25 May 2021 10:23:39 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefan Hajnoczi <stefanha@...hat.com>,
        virtualization@...ts.linux-foundation.org
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, slp@...hat.com,
        sgarzare@...hat.com, "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH 1/3] virtio: add virtioqueue_more_used()


在 2021/5/20 下午10:13, Stefan Hajnoczi 写道:
> Add an API to check whether there are pending used buffers. There is
> already a similar API called virtqueue_poll() but it only works together
> with virtqueue_enable_cb_prepare(). The patches that follow add blk-mq
> ->poll() support to virtio_blk and they need to check for used buffers
> without re-enabling virtqueue callbacks, so introduce an API for it.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>


Typo in the subject.


> ---
>   include/linux/virtio.h       |  2 ++
>   drivers/virtio/virtio_ring.c | 17 +++++++++++++++++
>   2 files changed, 19 insertions(+)
>
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index b1894e0323fa..c6ad0f25f412 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -63,6 +63,8 @@ bool virtqueue_kick_prepare(struct virtqueue *vq);
>   
>   bool virtqueue_notify(struct virtqueue *vq);
>   
> +bool virtqueue_more_used(const struct virtqueue *vq);
> +
>   void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
>   
>   void *virtqueue_get_buf_ctx(struct virtqueue *vq, unsigned int *len,
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 71e16b53e9c1..7c3da75da462 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2032,6 +2032,23 @@ static inline bool more_used(const struct vring_virtqueue *vq)
>   	return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq);
>   }
>   
> +/**
> + * virtqueue_more_used - check if there are used buffers pending
> + * @_vq: the struct virtqueue we're talking about.
> + *
> + * Returns true if there are used buffers, false otherwise. May be called at
> + * the same time as other virtqueue operations, but actually calling
> + * virtqueue_get_buf() requires serialization so be mindful of the race between
> + * calling virtqueue_more_used() and virtqueue_get_buf().
> + */
> +bool virtqueue_more_used(const struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	return more_used(vq);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_more_used);


It's worth to mention that the function is not serialized (no barriers).

Thanks


> +
>   irqreturn_t vring_interrupt(int irq, void *_vq)
>   {
>   	struct vring_virtqueue *vq = to_vvq(_vq);