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

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Date:   Tue, 25 May 2021 09:48:12 +0100
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        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()

On Tue, May 25, 2021 at 10:23:39AM +0800, Jason Wang wrote:
> 
> 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.

Thanks, will fix.

> > +/**
> > + * 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, will fix.

Stefan

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