Virtualization - Dec 2014 - [PATCH RFC 1/2] virtio_balloon: convert to virtio 1.0 endian-ness

balloon device is not part of virtio 1.0 spec.  Still, it's easy enough
to make it handle endian-ness exactly as other virtio 1.0 devices: what
we gain from this, is that there's no need to special-case it in virtio
core.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/uapi/linux/virtio_balloon.h | 5 +++--
 drivers/virtio/virtio_balloon.c     | 4 ++--
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/virtio_balloon.h
b/include/uapi/linux/virtio_balloon.h
index 5e26f61..5bee71c 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -27,6 +27,7 @@
  * SUCH DAMAGE. */
 #include <linux/virtio_ids.h>
 #include <linux/virtio_config.h>
+#include <linux/virtio_types.h>
 
 /* The feature bitmap for virtio balloon */
 #define VIRTIO_BALLOON_F_MUST_TELL_HOST	0 /* Tell before reclaiming pages */
@@ -52,8 +53,8 @@ struct virtio_balloon_config
 #define VIRTIO_BALLOON_S_NR       6
 
 struct virtio_balloon_stat {
-	__u16 tag;
-	__u64 val;
+	__virtio16 tag;
+	__virtio64 val;
 } __attribute__((packed));
 
 #endif /* _LINUX_VIRTIO_BALLOON_H */
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 4497def..721e32f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -201,8 +201,8 @@ static inline void update_stat(struct virtio_balloon *vb,
int idx,
 			       u16 tag, u64 val)
 {
 	BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
-	vb->stats[idx].tag = tag;
-	vb->stats[idx].val = val;
+	vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);
+	vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
 }
 
 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
-- 
MST

balloon is the only driver using legacy_only ATM.
It turns out, it's easier to just make balloon support virtio 1.0
endian-ness and drop the flag from core.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/linux/virtio.h          | 2 --
 drivers/virtio/virtio.c         | 4 ----
 drivers/virtio/virtio_balloon.c | 1 -
 3 files changed, 7 deletions(-)

diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 2bbf626..f70411e 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -132,7 +132,6 @@ int virtio_device_restore(struct virtio_device *dev);
  * @feature_table_size: number of entries in the feature table array.
  * @feature_table_legacy: same as feature_table but when working in legacy
mode.
  * @feature_table_size_legacy: number of entries in feature table legacy array.
- * @legacy_only: driver does not support virtio 1.0.
  * @probe: the function to call when a device is found.  Returns 0 or -errno.
  * @remove: the function to call when a device is removed.
  * @config_changed: optional function to call when the device configuration
@@ -145,7 +144,6 @@ struct virtio_driver {
 	unsigned int feature_table_size;
 	const unsigned int *feature_table_legacy;
 	unsigned int feature_table_size_legacy;
-	bool legacy_only;
 	int (*probe)(struct virtio_device *dev);
 	void (*scan)(struct virtio_device *dev);
 	void (*remove)(struct virtio_device *dev);
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index fa6b75d..2e836d8 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -197,10 +197,6 @@ static int virtio_dev_probe(struct device *_d)
 		driver_features_legacy = driver_features;
 	}
 
-	/* Detect legacy-only drivers and disable VIRTIO_F_VERSION_1. */
-	if (drv->legacy_only)
-		device_features &= ~(1ULL << VIRTIO_F_VERSION_1);
-
 	if (device_features & (1ULL << VIRTIO_F_VERSION_1))
 		dev->features = driver_features & device_features;
 	else
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 721e32f..fed3709 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -518,7 +518,6 @@ static unsigned int features[] = {
 };
 
 static struct virtio_driver virtio_balloon_driver = {
-	.legacy_only = true,
 	.feature_table = features,
 	.feature_table_size = ARRAY_SIZE(features),
 	.driver.name =	KBUILD_MODNAME,
-- 
MST

On Tue, 2 Dec 2014 13:44:06 +0200
"Michael S. Tsirkin" <mst at redhat.com> wrote:
> balloon device is not part of virtio 1.0 spec.  Still, it's easy enough
> to make it handle endian-ness exactly as other virtio 1.0 devices: what
> we gain from this, is that there's no need to special-case it in virtio
> core.
Well, the balloon is weird in a number of ways, including its always
little-endian config space.

But I'm not quite sure the spec covers this?
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  include/uapi/linux/virtio_balloon.h | 5 +++--
>  drivers/virtio/virtio_balloon.c     | 4 ++--
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
>  struct virtio_balloon_stat {
> -	__u16 tag;
> -	__u64 val;
> +	__virtio16 tag;
> +	__virtio64 val;
>  } __attribute__((packed));
Would the respective fields in the spec need updating? While it is
actually talking about legacy requirements, the fields are not
specified as __virtio{16,64}.

Also, is changing the stat fields enough? I've not looked into balloon
operation, but does the payload need some endianess conversion as well?

On Tue, Dec 02, 2014 at 07:39:30PM +0100, Cornelia Huck
wrote:
> On Tue, 2 Dec 2014 13:44:06 +0200
> "Michael S. Tsirkin" <mst at redhat.com> wrote:
> 
> > balloon device is not part of virtio 1.0 spec.  Still, it's easy
enough
> > to make it handle endian-ness exactly as other virtio 1.0 devices:
what
> > we gain from this, is that there's no need to special-case it in
virtio
> > core.
> 
> Well, the balloon is weird in a number of ways, including its always
> little-endian config space.
Hmm yes, I forgot about that.
> But I'm not quite sure the spec covers this?
The spec does not cover balloon.  It merely includes a reference section
about legacy balloon device.  What to do when that device sets VERSION_1
is really up to us.

Patchset v8 simply makes balloon tell core it's legacy_only.
This is I guess fine as far as it goes.
I was still looking for the best way that involves minimal noise
in core. This looked like the best way: change 4 lines,
and drop all special casing in core, but given the config space
endian-ness mess, I'm not sure anymore.
I guess we'll just stick to what v8 does for now.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> > ---
> >  include/uapi/linux/virtio_balloon.h | 5 +++--
> >  drivers/virtio/virtio_balloon.c     | 4 ++--
> >  2 files changed, 5 insertions(+), 4 deletions(-)
> > 
> 
> >  struct virtio_balloon_stat {
> > -	__u16 tag;
> > -	__u64 val;
> > +	__virtio16 tag;
> > +	__virtio64 val;
> >  } __attribute__((packed));
> 
> Would the respective fields in the spec need updating? While it is
> actually talking about legacy requirements, the fields are not
> specified as __virtio{16,64}.
> 
> Also, is changing the stat fields enough? I've not looked into balloon
> operation, but does the payload need some endianess conversion as well?