Linux Virtualization - Nov 2014 - [PATCH v6 01/46] virtio: add low-level APIs for feature bits

Add low level APIs to test/set/clear feature bits.
For use by transports, to make it easier to
write code independent of feature bit array format.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/linux/virtio_config.h | 53 ++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 50 insertions(+), 3 deletions(-)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7f4ef66..249fcd6 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -77,11 +77,47 @@ void virtio_check_driver_offered_feature(const struct
virtio_device *vdev,
 					 unsigned int fbit);
 
 /**
- * virtio_has_feature - helper to determine if this device has this feature.
+ * __virtio_test_bit - helper to test feature bits. For use by transports.
+ *                     Devices should normally use virtio_has_feature,
+ *                     which includes more checks.
  * @vdev: the device
  * @fbit: the feature bit
  */
-static inline bool virtio_has_feature(const struct virtio_device *vdev,
+static inline bool __virtio_test_bit(const struct virtio_device *vdev,
+				     unsigned int fbit)
+{
+	/* Did you forget to fix assumptions on max features? */
+	if (__builtin_constant_p(fbit))
+		BUILD_BUG_ON(fbit >= 32);
+	else
+		BUG_ON(fbit >= 32);
+
+	return test_bit(fbit, vdev->features);
+}
+
+/**
+ * __virtio_set_bit - helper to set feature bits. For use by transports.
+ * @vdev: the device
+ * @fbit: the feature bit
+ */
+static inline void __virtio_set_bit(struct virtio_device *vdev,
+				    unsigned int fbit)
+{
+	/* Did you forget to fix assumptions on max features? */
+	if (__builtin_constant_p(fbit))
+		BUILD_BUG_ON(fbit >= 32);
+	else
+		BUG_ON(fbit >= 32);
+
+	set_bit(fbit, vdev->features);
+}
+
+/**
+ * __virtio_clear_bit - helper to set feature bits. For use by transports.
+ * @vdev: the device
+ * @fbit: the feature bit
+ */
+static inline void __virtio_clear_bit(struct virtio_device *vdev,
 				      unsigned int fbit)
 {
 	/* Did you forget to fix assumptions on max features? */
@@ -90,10 +126,21 @@ static inline bool virtio_has_feature(const struct
virtio_device *vdev,
 	else
 		BUG_ON(fbit >= 32);
 
+	clear_bit(fbit, vdev->features);
+}
+
+/**
+ * virtio_has_feature - helper to determine if this device has this feature.
+ * @vdev: the device
+ * @fbit: the feature bit
+ */
+static inline bool virtio_has_feature(const struct virtio_device *vdev,
+				      unsigned int fbit)
+{
 	if (fbit < VIRTIO_TRANSPORT_F_START)
 		virtio_check_driver_offered_feature(vdev, fbit);
 
-	return test_bit(fbit, vdev->features);
+	return __virtio_test_bit(vdev, fbit);
 }
 
 static inline
-- 
MST

On Thu, 27 Nov 2014 22:07:36 +0200
"Michael S. Tsirkin" <mst at redhat.com> wrote:
> Add low level APIs to test/set/clear feature bits.
> For use by transports, to make it easier to
> write code independent of feature bit array format.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  include/linux/virtio_config.h | 53
++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 50 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 7f4ef66..249fcd6 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -77,11 +77,47 @@ void virtio_check_driver_offered_feature(const struct
virtio_device *vdev,
>  					 unsigned int fbit);
> 
>  /**
> - * virtio_has_feature - helper to determine if this device has this
feature.
> + * __virtio_test_bit - helper to test feature bits. For use by transports.
> + *                     Devices should normally use virtio_has_feature,
> + *                     which includes more checks.
>   * @vdev: the device
>   * @fbit: the feature bit
>   */
> -static inline bool virtio_has_feature(const struct virtio_device *vdev,
> +static inline bool __virtio_test_bit(const struct virtio_device *vdev,
> +				     unsigned int fbit)
> +{
> +	/* Did you forget to fix assumptions on max features? */
> +	if (__builtin_constant_p(fbit))
> +		BUILD_BUG_ON(fbit >= 32);
> +	else
> +		BUG_ON(fbit >= 32);
Does this want to be a helper? Might be overkill, but I'm always wary
of changes that need to be applied manually in many different places :)
> +
> +	return test_bit(fbit, vdev->features);
> +}
> +
> +/**
> + * __virtio_set_bit - helper to set feature bits. For use by transports.
> + * @vdev: the device
> + * @fbit: the feature bit
> + */
> +static inline void __virtio_set_bit(struct virtio_device *vdev,
> +				    unsigned int fbit)
> +{
> +	/* Did you forget to fix assumptions on max features? */
> +	if (__builtin_constant_p(fbit))
> +		BUILD_BUG_ON(fbit >= 32);
> +	else
> +		BUG_ON(fbit >= 32);
> +
> +	set_bit(fbit, vdev->features);
> +}
> +
> +/**
> + * __virtio_clear_bit - helper to set feature bits. For use by transports.
s/set/clear/
> + * @vdev: the device
> + * @fbit: the feature bit
> + */
> +static inline void __virtio_clear_bit(struct virtio_device *vdev,
>  				      unsigned int fbit)
>  {
>  	/* Did you forget to fix assumptions on max features? */
> @@ -90,10 +126,21 @@ static inline bool virtio_has_feature(const struct
virtio_device *vdev,
>  	else
>  		BUG_ON(fbit >= 32);
> 
> +	clear_bit(fbit, vdev->features);
> +}
> +
> +/**
> + * virtio_has_feature - helper to determine if this device has this
feature.
> + * @vdev: the device
> + * @fbit: the feature bit
> + */
> +static inline bool virtio_has_feature(const struct virtio_device *vdev,
> +				      unsigned int fbit)
> +{
>  	if (fbit < VIRTIO_TRANSPORT_F_START)
>  		virtio_check_driver_offered_feature(vdev, fbit);
> 
> -	return test_bit(fbit, vdev->features);
> +	return __virtio_test_bit(vdev, fbit);
>  }
> 
>  static inline

> Add low level APIs to test/set/clear feature bits.
> For use by transports, to make it easier to
> write code independent of feature bit array format.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  include/linux/virtio_config.h | 53
++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 50 insertions(+), 3 deletions(-)
> 
As these functions really set feature bits, I would rather name them:

virtio_has_feature ...
virtio_set_feature ...
virtio_clear_feature ...

But in general, this looks good to me!

On Fri, Nov 28, 2014 at 11:02:20AM +0100, Cornelia Huck
wrote:
> On Thu, 27 Nov 2014 22:07:36 +0200
> "Michael S. Tsirkin" <mst at redhat.com> wrote:
> 
> > Add low level APIs to test/set/clear feature bits.
> > For use by transports, to make it easier to
> > write code independent of feature bit array format.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> > ---
> >  include/linux/virtio_config.h | 53
++++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 50 insertions(+), 3 deletions(-)
> > 
> > diff --git a/include/linux/virtio_config.h
b/include/linux/virtio_config.h
> > index 7f4ef66..249fcd6 100644
> > --- a/include/linux/virtio_config.h
> > +++ b/include/linux/virtio_config.h
> > @@ -77,11 +77,47 @@ void virtio_check_driver_offered_feature(const
struct virtio_device *vdev,
> >  					 unsigned int fbit);
> > 
> >  /**
> > - * virtio_has_feature - helper to determine if this device has this
feature.
> > + * __virtio_test_bit - helper to test feature bits. For use by
transports.
> > + *                     Devices should normally use
virtio_has_feature,
> > + *                     which includes more checks.
> >   * @vdev: the device
> >   * @fbit: the feature bit
> >   */
> > -static inline bool virtio_has_feature(const struct virtio_device
*vdev,
> > +static inline bool __virtio_test_bit(const struct virtio_device
*vdev,
> > +				     unsigned int fbit)
> > +{
> > +	/* Did you forget to fix assumptions on max features? */
> > +	if (__builtin_constant_p(fbit))
> > +		BUILD_BUG_ON(fbit >= 32);
> > +	else
> > +		BUG_ON(fbit >= 32);
> 
> Does this want to be a helper? Might be overkill, but I'm always wary
> of changes that need to be applied manually in many different places :)
I'm not sure.  It's just an assert, if it's not obvious
what it checks then it doesn't serve a useful purpose.
> > +
> > +	return test_bit(fbit, vdev->features);
> > +}
> > +
> > +/**
> > + * __virtio_set_bit - helper to set feature bits. For use by
transports.
> > + * @vdev: the device
> > + * @fbit: the feature bit
> > + */
> > +static inline void __virtio_set_bit(struct virtio_device *vdev,
> > +				    unsigned int fbit)
> > +{
> > +	/* Did you forget to fix assumptions on max features? */
> > +	if (__builtin_constant_p(fbit))
> > +		BUILD_BUG_ON(fbit >= 32);
> > +	else
> > +		BUG_ON(fbit >= 32);
> > +
> > +	set_bit(fbit, vdev->features);
> > +}
> > +
> > +/**
> > + * __virtio_clear_bit - helper to set feature bits. For use by
transports.
> 
> s/set/clear/
Good catch, thanks.
> > + * @vdev: the device
> > + * @fbit: the feature bit
> > + */
> > +static inline void __virtio_clear_bit(struct virtio_device *vdev,
> >  				      unsigned int fbit)
> >  {
> >  	/* Did you forget to fix assumptions on max features? */
> > @@ -90,10 +126,21 @@ static inline bool virtio_has_feature(const
struct virtio_device *vdev,
> >  	else
> >  		BUG_ON(fbit >= 32);
> > 
> > +	clear_bit(fbit, vdev->features);
> > +}
> > +
> > +/**
> > + * virtio_has_feature - helper to determine if this device has this
feature.
> > + * @vdev: the device
> > + * @fbit: the feature bit
> > + */
> > +static inline bool virtio_has_feature(const struct virtio_device
*vdev,
> > +				      unsigned int fbit)
> > +{
> >  	if (fbit < VIRTIO_TRANSPORT_F_START)
> >  		virtio_check_driver_offered_feature(vdev, fbit);
> > 
> > -	return test_bit(fbit, vdev->features);
> > +	return __virtio_test_bit(vdev, fbit);
> >  }
> > 
> >  static inline

On Fri, Nov 28, 2014 at 01:10:57PM +0100, David Hildenbrand
wrote:
> > Add low level APIs to test/set/clear feature bits.
> > For use by transports, to make it easier to
> > write code independent of feature bit array format.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> > ---
> >  include/linux/virtio_config.h | 53
++++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 50 insertions(+), 3 deletions(-)
> > 
> 
> As these functions really set feature bits, I would rather name them:
> 
> virtio_has_feature ...
> virtio_set_feature ...
> virtio_clear_feature ...
We have these as high level APIs for drivers.
These are low level ones so need a different
name.

> But in general, this looks good to me!