linux-kernel - Re: [PATCH v6 01/46] virtio: add low-level APIs for feature bits

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Message-ID: <20141128110220.741c11af.cornelia.huck@de.ibm.com>
Date:	Fri, 28 Nov 2014 11:02:20 +0100
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	rusty@....ibm.com, nab@...ux-iscsi.org, pbonzini@...hat.com,
	thuth@...ux.vnet.ibm.com, dahi@...ux.vnet.ibm.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v6 01/46] virtio: add low-level APIs for feature bits

On Thu, 27 Nov 2014 22:07:36 +0200
"Michael S. Tsirkin" <mst@...hat.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@...hat.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

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