Re: [PATCH vhost v3 1/4] virtio: find_vqs: pass struct instead of multi parameters

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On Tue, Mar 12, 2024 at 10:10 AM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> 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.
> Because the vp_modern_create_avq() use the "const char *names[]",
> and the virtio_uml.c changes the name in the subsequent commit, so
> change the "names" inside the virtio_vq_config from "const char *const
> *names" to "const char **names".
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> Acked-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
> Reviewed-by: Ilpo J=E4rvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>

The name seems broken here.


>  typedef void vq_callback_t(struct virtqueue *);
> +/**
> + * struct virtio_vq_config - configure for find_vqs()
> + * @cfg_idx: Used by virtio core. The drivers should set this to 0.
> + *     During the initialization of each vq(vring setup), we need to know which
> + *     item in the array should be used at that time. But since the item in
> + *     names can be null, which causes some item of array to be skipped, we
> + *     cannot use vq.index as the current id. So add a cfg_idx to let vring
> + *     know how to get the current configuration from the array when
> + *     initializing vq.

So this design is not good. If it is not something that the driver
needs to care about, the core needs to hide it from the API.


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