diff mbox series

[vhost,v9,1/6] virtio_balloon: remove the dependence where names[] is null

Message ID 20240424091533.86949-2-xuanzhuo@linux.alibaba.com (mailing list archive)
State New, archived
Headers show
Series refactor the params of find_vqs() | expand

Commit Message

Xuan Zhuo April 24, 2024, 9:15 a.m. UTC 
Currently, the init_vqs function within the virtio_balloon driver relies
on the condition that certain names array entries are null in order to
skip the initialization of some virtual queues (vqs). This behavior is
unique to this part of the codebase. In an upcoming commit, we plan to
eliminate this dependency by removing the function entirely. Therefore,
with this change, we are ensuring that the virtio_balloon no longer
depends on the aforementioned function.

As specification 1.0-1.2, vq indexes should not be contiguous if some
vq does not exist. But currently the virtqueue index is contiguous for
all existing devices. The Linux kernel does not implement functionality
to allow vq indexes to be discontinuous. So the current behavior of the
virtio-balloon device is different for the spec. But this commit has no
functional changes.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
---
 drivers/virtio/virtio_balloon.c | 48 ++++++++++++++-------------------
 1 file changed, 20 insertions(+), 28 deletions(-)

Comments

Michael S. Tsirkin June 20, 2024, 8:08 a.m. UTC | #1 
On Wed, Apr 24, 2024 at 05:15:28PM +0800, Xuan Zhuo wrote:
> Currently, the init_vqs function within the virtio_balloon driver relies
> on the condition that certain names array entries are null in order to
> skip the initialization of some virtual queues (vqs). This behavior is
> unique to this part of the codebase. In an upcoming commit, we plan to
> eliminate this dependency by removing the function entirely. Therefore,
> with this change, we are ensuring that the virtio_balloon no longer
> depends on the aforementioned function.
> 
> As specification 1.0-1.2, vq indexes should not be contiguous if some
> vq does not exist. But currently the virtqueue index is contiguous for
> all existing devices. The Linux kernel does not implement functionality
> to allow vq indexes to be discontinuous. So the current behavior of the
> virtio-balloon device is different for the spec. But this commit has no
> functional changes.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Acked-by: Jason Wang <jasowang@redhat.com>

I can't make heads of tails of this.

David you acked so maybe you can help rewrite the commit log here?

I don't understand what this says.
What in the balloon driver is out of spec?
NULL in names *exactly* allows skipping init for some vqs.
How is that "does not implement"?

And so on.


> ---
>  drivers/virtio/virtio_balloon.c | 48 ++++++++++++++-------------------
>  1 file changed, 20 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index c0a63638f95e..ccda6d08493f 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -548,49 +548,41 @@ static int init_vqs(struct virtio_balloon *vb)
>  	struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX];
>  	vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
>  	const char *names[VIRTIO_BALLOON_VQ_MAX];
> -	int err;
> +	int err, idx = 0;
>  
> -	/*
> -	 * Inflateq and deflateq are used unconditionally. The names[]
> -	 * will be NULL if the related feature is not enabled, which will
> -	 * cause no allocation for the corresponding virtqueue in find_vqs.
> -	 */
> -	callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
> -	names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
> -	callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
> -	names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
> -	callbacks[VIRTIO_BALLOON_VQ_STATS] = NULL;
> -	names[VIRTIO_BALLOON_VQ_STATS] = NULL;
> -	callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> -	names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> -	names[VIRTIO_BALLOON_VQ_REPORTING] = NULL;
> +	callbacks[idx] = balloon_ack;
> +	names[idx++] = "inflate";
> +	callbacks[idx] = balloon_ack;
> +	names[idx++] = "deflate";
>  
>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> -		names[VIRTIO_BALLOON_VQ_STATS] = "stats";
> -		callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
> +		names[idx] = "stats";
> +		callbacks[idx++] = stats_request;
>  	}
>  
>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> -		names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
> -		callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> +		names[idx] = "free_page_vq";
> +		callbacks[idx++] = NULL;
>  	}
>  
>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
> -		names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq";
> -		callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack;
> +		names[idx] = "reporting_vq";
> +		callbacks[idx++] = balloon_ack;
>  	}
>  
> -	err = virtio_find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, vqs,
> -			      callbacks, names, NULL);
> +	err = virtio_find_vqs(vb->vdev, idx, vqs, callbacks, names, NULL);
>  	if (err)
>  		return err;
>  
> -	vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
> -	vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
> +	idx = 0;
> +
> +	vb->inflate_vq = vqs[idx++];
> +	vb->deflate_vq = vqs[idx++];
> +
>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
>  		struct scatterlist sg;
>  		unsigned int num_stats;
> -		vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
> +		vb->stats_vq = vqs[idx++];
>  
>  		/*
>  		 * Prime this virtqueue with one buffer so the hypervisor can
> @@ -610,10 +602,10 @@ static int init_vqs(struct virtio_balloon *vb)
>  	}
>  
>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
> -		vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
> +		vb->free_page_vq = vqs[idx++];
>  
>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
> -		vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING];
> +		vb->reporting_vq = vqs[idx++];
>  
>  	return 0;
>  }
> -- 
> 2.32.0.3.g01195cf9f
Jason Wang June 20, 2024, 8:21 a.m. UTC | #2 
On Thu, Jun 20, 2024 at 4:08 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Wed, Apr 24, 2024 at 05:15:28PM +0800, Xuan Zhuo wrote:
> > Currently, the init_vqs function within the virtio_balloon driver relies
> > on the condition that certain names array entries are null in order to
> > skip the initialization of some virtual queues (vqs). This behavior is
> > unique to this part of the codebase. In an upcoming commit, we plan to
> > eliminate this dependency by removing the function entirely. Therefore,
> > with this change, we are ensuring that the virtio_balloon no longer
> > depends on the aforementioned function.
> >
> > As specification 1.0-1.2, vq indexes should not be contiguous if some
> > vq does not exist. But currently the virtqueue index is contiguous for
> > all existing devices. The Linux kernel does not implement functionality
> > to allow vq indexes to be discontinuous. So the current behavior of the
> > virtio-balloon device is different for the spec. But this commit has no
> > functional changes.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > Acked-by: David Hildenbrand <david@redhat.com>
> > Acked-by: Jason Wang <jasowang@redhat.com>
>
> I can't make heads of tails of this.
>
> David you acked so maybe you can help rewrite the commit log here?
>
> I don't understand what this says.
> What in the balloon driver is out of spec?

The problem is the spec has bug, see this:

https://www.mail-archive.com/linux-um@lists.infradead.org/msg04359.html

Thanks


> NULL in names *exactly* allows skipping init for some vqs.
> How is that "does not implement"?
>
> And so on.
>
>
> > ---
> >  drivers/virtio/virtio_balloon.c | 48 ++++++++++++++-------------------
> >  1 file changed, 20 insertions(+), 28 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index c0a63638f95e..ccda6d08493f 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -548,49 +548,41 @@ static int init_vqs(struct virtio_balloon *vb)
> >       struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX];
> >       vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
> >       const char *names[VIRTIO_BALLOON_VQ_MAX];
> > -     int err;
> > +     int err, idx = 0;
> >
> > -     /*
> > -      * Inflateq and deflateq are used unconditionally. The names[]
> > -      * will be NULL if the related feature is not enabled, which will
> > -      * cause no allocation for the corresponding virtqueue in find_vqs.
> > -      */
> > -     callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
> > -     names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
> > -     callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
> > -     names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
> > -     callbacks[VIRTIO_BALLOON_VQ_STATS] = NULL;
> > -     names[VIRTIO_BALLOON_VQ_STATS] = NULL;
> > -     callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> > -     names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> > -     names[VIRTIO_BALLOON_VQ_REPORTING] = NULL;
> > +     callbacks[idx] = balloon_ack;
> > +     names[idx++] = "inflate";
> > +     callbacks[idx] = balloon_ack;
> > +     names[idx++] = "deflate";
> >
> >       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> > -             names[VIRTIO_BALLOON_VQ_STATS] = "stats";
> > -             callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
> > +             names[idx] = "stats";
> > +             callbacks[idx++] = stats_request;
> >       }
> >
> >       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> > -             names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
> > -             callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> > +             names[idx] = "free_page_vq";
> > +             callbacks[idx++] = NULL;
> >       }
> >
> >       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
> > -             names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq";
> > -             callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack;
> > +             names[idx] = "reporting_vq";
> > +             callbacks[idx++] = balloon_ack;
> >       }
> >
> > -     err = virtio_find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, vqs,
> > -                           callbacks, names, NULL);
> > +     err = virtio_find_vqs(vb->vdev, idx, vqs, callbacks, names, NULL);
> >       if (err)
> >               return err;
> >
> > -     vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
> > -     vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
> > +     idx = 0;
> > +
> > +     vb->inflate_vq = vqs[idx++];
> > +     vb->deflate_vq = vqs[idx++];
> > +
> >       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> >               struct scatterlist sg;
> >               unsigned int num_stats;
> > -             vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
> > +             vb->stats_vq = vqs[idx++];
> >
> >               /*
> >                * Prime this virtqueue with one buffer so the hypervisor can
> > @@ -610,10 +602,10 @@ static int init_vqs(struct virtio_balloon *vb)
> >       }
> >
> >       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
> > -             vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
> > +             vb->free_page_vq = vqs[idx++];
> >
> >       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
> > -             vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING];
> > +             vb->reporting_vq = vqs[idx++];
> >
> >       return 0;
> >  }
> > --
> > 2.32.0.3.g01195cf9f
>
diff mbox series

Patch

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index c0a63638f95e..ccda6d08493f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -548,49 +548,41 @@  static int init_vqs(struct virtio_balloon *vb)
 	struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX];
 	vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
 	const char *names[VIRTIO_BALLOON_VQ_MAX];
-	int err;
+	int err, idx = 0;
 
-	/*
-	 * Inflateq and deflateq are used unconditionally. The names[]
-	 * will be NULL if the related feature is not enabled, which will
-	 * cause no allocation for the corresponding virtqueue in find_vqs.
-	 */
-	callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
-	names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
-	callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
-	names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
-	callbacks[VIRTIO_BALLOON_VQ_STATS] = NULL;
-	names[VIRTIO_BALLOON_VQ_STATS] = NULL;
-	callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
-	names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
-	names[VIRTIO_BALLOON_VQ_REPORTING] = NULL;
+	callbacks[idx] = balloon_ack;
+	names[idx++] = "inflate";
+	callbacks[idx] = balloon_ack;
+	names[idx++] = "deflate";
 
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
-		names[VIRTIO_BALLOON_VQ_STATS] = "stats";
-		callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
+		names[idx] = "stats";
+		callbacks[idx++] = stats_request;
 	}
 
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
-		names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
-		callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
+		names[idx] = "free_page_vq";
+		callbacks[idx++] = NULL;
 	}
 
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
-		names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq";
-		callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack;
+		names[idx] = "reporting_vq";
+		callbacks[idx++] = balloon_ack;
 	}
 
-	err = virtio_find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, vqs,
-			      callbacks, names, NULL);
+	err = virtio_find_vqs(vb->vdev, idx, vqs, callbacks, names, NULL);
 	if (err)
 		return err;
 
-	vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
-	vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
+	idx = 0;
+
+	vb->inflate_vq = vqs[idx++];
+	vb->deflate_vq = vqs[idx++];
+
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 		struct scatterlist sg;
 		unsigned int num_stats;
-		vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
+		vb->stats_vq = vqs[idx++];
 
 		/*
 		 * Prime this virtqueue with one buffer so the hypervisor can
@@ -610,10 +602,10 @@  static int init_vqs(struct virtio_balloon *vb)
 	}
 
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
-		vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
+		vb->free_page_vq = vqs[idx++];
 
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
-		vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING];
+		vb->reporting_vq = vqs[idx++];
 
 	return 0;
 }