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[RFC,v3,05/12] virtio: introduce legacy virtio devices

Message ID 1417022923-1654-6-git-send-email-cornelia.huck@de.ibm.com
State New
Headers show

Commit Message

Cornelia Huck Nov. 26, 2014, 5:28 p.m. UTC 
Introduce a helper function to indicate  whether a virtio device is
operating in legacy or virtio standard mode.

It may be used to make decisions about the endianess of virtio accesses
and other virtio-1 specific changes, enabling us to support transitional
devices.

Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
---
 hw/virtio/virtio.c                |    6 +++++-
 include/hw/virtio/virtio-access.h |    4 ++++
 include/hw/virtio/virtio.h        |   13 +++++++++++--
 3 files changed, 20 insertions(+), 3 deletions(-)

Comments

Greg Kurz Nov. 26, 2014, 6:46 p.m. UTC | #1 
On Wed, 26 Nov 2014 18:28:36 +0100
Cornelia Huck <cornelia.huck@de.ibm.com> wrote:

> Introduce a helper function to indicate  whether a virtio device is
> operating in legacy or virtio standard mode.
> 
> It may be used to make decisions about the endianess of virtio accesses
> and other virtio-1 specific changes, enabling us to support transitional
> devices.
> 
> Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> ---
>  hw/virtio/virtio.c                |    6 +++++-
>  include/hw/virtio/virtio-access.h |    4 ++++
>  include/hw/virtio/virtio.h        |   13 +++++++++++--
>  3 files changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 2eb5d3c..4149f45 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -883,7 +883,11 @@ static bool virtio_device_endian_needed(void *opaque)
>      VirtIODevice *vdev = opaque;
> 
>      assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
> -    return vdev->device_endian != virtio_default_endian();
> +    if (virtio_device_is_legacy(vdev)) {
> +        return vdev->device_endian != virtio_default_endian();
> +    }
> +    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
> +    return vdev->device_endian != VIRTIO_DEVICE_ENDIAN_LITTLE;
>  }
> 

Sorry but I still don't understand why we need to stream the device_endian
subsection if we have a virtio-1 device... this field is only used on
legacy device paths. Can you share an example where it is needed ?

>  static const VMStateDescription vmstate_virtio_device_endian = {
> diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h
> index 46456fd..c123ee0 100644
> --- a/include/hw/virtio/virtio-access.h
> +++ b/include/hw/virtio/virtio-access.h
> @@ -19,6 +19,10 @@
> 
>  static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
>  {
> +    if (!virtio_device_is_legacy(vdev)) {
> +        /* Devices conforming to VIRTIO 1.0 or later are always LE. */
> +        return false;
> +    }
>  #if defined(TARGET_IS_BIENDIAN)
>      return virtio_is_big_endian(vdev);
>  #elif defined(TARGET_WORDS_BIGENDIAN)
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index b408166..40e567c 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -275,9 +275,18 @@ void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
>  void virtio_queue_notify_vq(VirtQueue *vq);
>  void virtio_irq(VirtQueue *vq);
> 
> +static inline bool virtio_device_is_legacy(VirtIODevice *vdev)
> +{
> +    return !(vdev->guest_features[1] & (1 << (VIRTIO_F_VERSION_1 - 32)));
> +}
> +
>  static inline bool virtio_is_big_endian(VirtIODevice *vdev)
>  {
> -    assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
> -    return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
> +    if (virtio_device_is_legacy(vdev)) {
> +        assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
> +        return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
> +    }
> +    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
> +    return false;
>  }
>  #endif
Michael S. Tsirkin Nov. 26, 2014, 6:51 p.m. UTC | #2 
On Wed, Nov 26, 2014 at 07:46:38PM +0100, Greg Kurz wrote:
> On Wed, 26 Nov 2014 18:28:36 +0100
> Cornelia Huck <cornelia.huck@de.ibm.com> wrote:
> 
> > Introduce a helper function to indicate  whether a virtio device is
> > operating in legacy or virtio standard mode.
> > 
> > It may be used to make decisions about the endianess of virtio accesses
> > and other virtio-1 specific changes, enabling us to support transitional
> > devices.
> > 
> > Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
> > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> > ---
> >  hw/virtio/virtio.c                |    6 +++++-
> >  include/hw/virtio/virtio-access.h |    4 ++++
> >  include/hw/virtio/virtio.h        |   13 +++++++++++--
> >  3 files changed, 20 insertions(+), 3 deletions(-)
> > 
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 2eb5d3c..4149f45 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -883,7 +883,11 @@ static bool virtio_device_endian_needed(void *opaque)
> >      VirtIODevice *vdev = opaque;
> > 
> >      assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
> > -    return vdev->device_endian != virtio_default_endian();
> > +    if (virtio_device_is_legacy(vdev)) {
> > +        return vdev->device_endian != virtio_default_endian();
> > +    }
> > +    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
> > +    return vdev->device_endian != VIRTIO_DEVICE_ENDIAN_LITTLE;
> >  }
> > 
> 
> Sorry but I still don't understand why we need to stream the device_endian
> subsection if we have a virtio-1 device... this field is only used on
> legacy device paths. Can you share an example where it is needed ?

I think it's needed.
A transitional device can be used with legacy native endian and
modern little endian format.


> >  static const VMStateDescription vmstate_virtio_device_endian = {
> > diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h
> > index 46456fd..c123ee0 100644
> > --- a/include/hw/virtio/virtio-access.h
> > +++ b/include/hw/virtio/virtio-access.h
> > @@ -19,6 +19,10 @@
> > 
> >  static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
> >  {
> > +    if (!virtio_device_is_legacy(vdev)) {
> > +        /* Devices conforming to VIRTIO 1.0 or later are always LE. */
> > +        return false;
> > +    }
> >  #if defined(TARGET_IS_BIENDIAN)
> >      return virtio_is_big_endian(vdev);
> >  #elif defined(TARGET_WORDS_BIGENDIAN)
> > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > index b408166..40e567c 100644
> > --- a/include/hw/virtio/virtio.h
> > +++ b/include/hw/virtio/virtio.h
> > @@ -275,9 +275,18 @@ void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
> >  void virtio_queue_notify_vq(VirtQueue *vq);
> >  void virtio_irq(VirtQueue *vq);
> > 
> > +static inline bool virtio_device_is_legacy(VirtIODevice *vdev)
> > +{
> > +    return !(vdev->guest_features[1] & (1 << (VIRTIO_F_VERSION_1 - 32)));
> > +}
> > +
> >  static inline bool virtio_is_big_endian(VirtIODevice *vdev)
> >  {
> > -    assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
> > -    return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
> > +    if (virtio_device_is_legacy(vdev)) {
> > +        assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
> > +        return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
> > +    }
> > +    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
> > +    return false;
> >  }
> >  #endif
diff mbox

Patch

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 2eb5d3c..4149f45 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -883,7 +883,11 @@  static bool virtio_device_endian_needed(void *opaque)
     VirtIODevice *vdev = opaque;
 
     assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
-    return vdev->device_endian != virtio_default_endian();
+    if (virtio_device_is_legacy(vdev)) {
+        return vdev->device_endian != virtio_default_endian();
+    }
+    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
+    return vdev->device_endian != VIRTIO_DEVICE_ENDIAN_LITTLE;
 }
 
 static const VMStateDescription vmstate_virtio_device_endian = {
diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h
index 46456fd..c123ee0 100644
--- a/include/hw/virtio/virtio-access.h
+++ b/include/hw/virtio/virtio-access.h
@@ -19,6 +19,10 @@ 
 
 static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
 {
+    if (!virtio_device_is_legacy(vdev)) {
+        /* Devices conforming to VIRTIO 1.0 or later are always LE. */
+        return false;
+    }
 #if defined(TARGET_IS_BIENDIAN)
     return virtio_is_big_endian(vdev);
 #elif defined(TARGET_WORDS_BIGENDIAN)
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index b408166..40e567c 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -275,9 +275,18 @@  void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
 void virtio_queue_notify_vq(VirtQueue *vq);
 void virtio_irq(VirtQueue *vq);
 
+static inline bool virtio_device_is_legacy(VirtIODevice *vdev)
+{
+    return !(vdev->guest_features[1] & (1 << (VIRTIO_F_VERSION_1 - 32)));
+}
+
 static inline bool virtio_is_big_endian(VirtIODevice *vdev)
 {
-    assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
-    return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
+    if (virtio_device_is_legacy(vdev)) {
+        assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
+        return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
+    }
+    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
+    return false;
 }
 #endif