Re: [PATCH vhost 1/4] virtio: find_vqs: pass struct instead of multi parameters

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Mon, 4 Mar 2024, Xuan Zhuo wrote:

> Now, we pass multi parameters to find_vqs. These parameters
> may work for transport or work for vring.
> 
> And find_vqs has multi implements in many places:
> 
>  arch/um/drivers/virtio_uml.c
>  drivers/platform/mellanox/mlxbf-tmfifo.c
>  drivers/remoteproc/remoteproc_virtio.c
>  drivers/s390/virtio/virtio_ccw.c
>  drivers/virtio/virtio_mmio.c
>  drivers/virtio/virtio_pci_legacy.c
>  drivers/virtio/virtio_pci_modern.c
>  drivers/virtio/virtio_vdpa.c
> 
> Every time, we try to add a new parameter, that is difficult.
> We must change every find_vqs implement.
> 
> One the other side, if we want to pass a parameter to vring,
> we must change the call path from transport to vring.
> Too many functions need to be changed.
> 
> So it is time to refactor the find_vqs. We pass a structure
> cfg to find_vqs(), that will be passed to vring by transport.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>  arch/um/drivers/virtio_uml.c             | 23 ++++-----
>  drivers/platform/mellanox/mlxbf-tmfifo.c | 13 ++----
>  drivers/remoteproc/remoteproc_virtio.c   | 28 ++++++-----
>  drivers/s390/virtio/virtio_ccw.c         | 29 ++++++------
>  drivers/virtio/virtio_mmio.c             | 26 +++++------
>  drivers/virtio/virtio_pci_common.c       | 59 +++++++++++-------------
>  drivers/virtio/virtio_pci_common.h       |  9 +---
>  drivers/virtio/virtio_pci_legacy.c       | 11 +++--
>  drivers/virtio/virtio_pci_modern.c       | 33 +++++++------
>  drivers/virtio/virtio_vdpa.c             | 36 +++++++--------
>  include/linux/virtio_config.h            | 51 ++++++++++++++++----
>  11 files changed, 172 insertions(+), 146 deletions(-)
> 
> diff --git a/arch/um/drivers/virtio_uml.c b/arch/um/drivers/virtio_uml.c
> index 8adca2000e51..c13dfeeb90c4 100644
> --- a/arch/um/drivers/virtio_uml.c
> +++ b/arch/um/drivers/virtio_uml.c
> @@ -937,8 +937,8 @@ static int vu_setup_vq_call_fd(struct virtio_uml_device *vu_dev,
>  }
>  
>  static struct virtqueue *vu_setup_vq(struct virtio_device *vdev,
> -				     unsigned index, vq_callback_t *callback,
> -				     const char *name, bool ctx)
> +				     unsigned index,
> +				     struct virtio_vq_config *cfg)
>  {
>  	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
>  	struct platform_device *pdev = vu_dev->pdev;
> @@ -953,10 +953,12 @@ static struct virtqueue *vu_setup_vq(struct virtio_device *vdev,
>  		goto error_kzalloc;
>  	}
>  	snprintf(info->name, sizeof(info->name), "%s.%d-%s", pdev->name,
> -		 pdev->id, name);
> +		 pdev->id, cfg->names[cfg->cfg_idx]);
>  
>  	vq = vring_create_virtqueue(index, num, PAGE_SIZE, vdev, true, true,
> -				    ctx, vu_notify, callback, info->name);
> +				    cfg->ctx ? cfg->ctx[cfg->cfg_idx] : false,

Based on the commit message, I don't understand why this transformation 
was made. It's perhaps some artifact of moving things around but please 
state it in the commit message because this isn't 1:1 transformation 
which would be just ctx -> cfg->ctx

> +				    vu_notify,
> +				    cfg->callbacks[cfg->cfg_idx], info->name);
>  	if (!vq) {
>  		rc = -ENOMEM;
>  		goto error_create;


> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> index b655fccaf773..a9ae03904dcf 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -172,9 +172,7 @@ static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
>  }
>  
>  static struct virtqueue *vp_setup_vq(struct virtio_device *vdev, unsigned int index,
> -				     void (*callback)(struct virtqueue *vq),
> -				     const char *name,
> -				     bool ctx,
> +				     struct virtio_vq_config *cfg,
>  				     u16 msix_vec)
>  {
>  	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> @@ -186,13 +184,13 @@ static struct virtqueue *vp_setup_vq(struct virtio_device *vdev, unsigned int in
>  	if (!info)
>  		return ERR_PTR(-ENOMEM);
>  
> -	vq = vp_dev->setup_vq(vp_dev, info, index, callback, name, ctx,
> +	vq = vp_dev->setup_vq(vp_dev, info, index, cfg,
>  			      msix_vec);

Should now easily fit to one line.


> @@ -126,10 +124,7 @@ bool vp_notify(struct virtqueue *vq);
>  /* the config->del_vqs() implementation */
>  void vp_del_vqs(struct virtio_device *vdev);
>  /* the config->find_vqs() implementation */
> -int vp_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
> -		struct virtqueue *vqs[], vq_callback_t *callbacks[],
> -		const char * const names[], const bool *ctx,
> -		struct irq_affinity *desc);
> +int vp_find_vqs(struct virtio_device *vdev, struct virtio_vq_config *cfg);

Without knowing better, do you expect cfg is mutated inside vp_find_vqs()? 
If not, mark it as const.

> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index da9b271b54db..1df8634d1258 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -96,6 +96,20 @@ typedef void vq_callback_t(struct virtqueue *);
>   * @create_avq: create admin virtqueue resource.
>   * @destroy_avq: destroy admin virtqueue resource.
>   */
> +
> +struct virtio_vq_config {
> +	unsigned int nvqs;
> +
> +	/* the vq index may not eq to the cfg index of the other array items */

Can you try to make this comment clearer, as is I don't understand what it 
means. E.g. what is "the other array"? not eq = not equal ?

> +	unsigned int cfg_idx;
> +
> +	struct virtqueue **vqs;
> +	vq_callback_t **callbacks;
> +	const char *const *names;
> +	const bool *ctx;
> +	struct irq_affinity *desc;
> +};

The placement of the struct is wrong. Now the documentation of struct 
virtio_config_ops is above your struct!?!

Please also document the members of the newly added struct with kerneldoc.

> +
>  struct virtio_config_ops {
>  	void (*get)(struct virtio_device *vdev, unsigned offset,
>  		    void *buf, unsigned len);
> @@ -105,10 +119,7 @@ struct virtio_config_ops {
>  	u8 (*get_status)(struct virtio_device *vdev);
>  	void (*set_status)(struct virtio_device *vdev, u8 status);
>  	void (*reset)(struct virtio_device *vdev);
> -	int (*find_vqs)(struct virtio_device *, unsigned nvqs,
> -			struct virtqueue *vqs[], vq_callback_t *callbacks[],
> -			const char * const names[], const bool *ctx,
> -			struct irq_affinity *desc);
> +	int (*find_vqs)(struct virtio_device *vdev, struct virtio_vq_config *cfg);
>  	void (*del_vqs)(struct virtio_device *);
>  	void (*synchronize_cbs)(struct virtio_device *);
>  	u64 (*get_features)(struct virtio_device *vdev);


-- 
 i.