Re: [PATCH v4 2/8] media: virtio: Add virtio-media driver structs and function declarations

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jun 22, 2026 at 04:43:37PM -0400, Brian Daniels wrote:
> From: Alexandre Courbot <gnurou@gmail.com>
> 
> Add the structs and function declarations for the new virtio-media drvier.
> 
> Signed-off-by: Alexandre Courbot <gnurou@gmail.com>
> Co-developed-by: Brian Daniels <briandaniels@google.com>
> Signed-off-by: Brian Daniels <briandaniels@google.com>
> ---
>  drivers/media/virtio/virtio_media.h | 95 +++++++++++++++++++++++++++++
>  1 file changed, 95 insertions(+)
>  create mode 100644 drivers/media/virtio/virtio_media.h
> 
> diff --git a/drivers/media/virtio/virtio_media.h b/drivers/media/virtio/virtio_media.h
> new file mode 100644
> index 000000000..52809d4e9
> --- /dev/null
> +++ b/drivers/media/virtio/virtio_media.h
> @@ -0,0 +1,95 @@
> +/* SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0+ */
> +
> +/*
> + * Virtio-media structures & functions declarations.
> + *
> + * Copyright (c) 2024-2025 Google LLC.
> + */
> +
> +#ifndef __VIRTIO_MEDIA_H
> +#define __VIRTIO_MEDIA_H
> +
> +#include <linux/virtio_config.h>
> +#include <media/v4l2-device.h>
> +
> +#include "protocol.h"
> +
> +#define DESC_CHAIN_MAX_LEN SG_MAX_SINGLE_ALLOC
> +
> +#define VIRTIO_MEDIA_DEFAULT_DRIVER_NAME "virtio-media"
> +
> +extern char *virtio_media_driver_name;
> +extern bool virtio_media_allow_userptr;
> +
> +/**
> + * struct virtio_media - Virtio-media device.
> + * @v4l2_dev: v4l2_device for the media device.
> + * @video_dev: video_device for the media device.
> + * @virtio_dev: virtio device for the media device.
> + * @commandq: virtio command queue.
> + * @eventq: virtio event queue.
> + * @eventq_work: work to run when events are received on @eventq.
> + * @mmap_region: region into which MMAP buffers are mapped by the host.
> + * @event_buffer: buffer for event descriptors.
> + * @sessions: list of active sessions on the device.
> + * @sessions_lock: protects @sessions and ``virtio_media_session::list``.
> + * @events_lock: prevents concurrent processing of events.
> + * @cmd: union of the device commands "open" and "munmap". The other
> + *       commands are handled by @struct virtio_media_session
> + * @resp: union of responses.to device commands "open" and "munmap". The
> + *        other responses are handled by @struct virtio_media_session
> + * @vlock: serializes access to the command queue.
> + * @wq: waitqueue for host responses on the command queue.
> + */
> +struct virtio_media {
> +	struct v4l2_device v4l2_dev;
> +	struct video_device video_dev;
> +
> +	struct virtio_device *virtio_dev;
> +	struct virtqueue *commandq;
> +	struct virtqueue *eventq;
> +	struct work_struct eventq_work;
> +
> +	struct virtio_shm_region mmap_region;
> +
> +	void *event_buffer;
> +
> +	struct list_head sessions;
> +	struct mutex sessions_lock; /* protects sessions list */
> +
> +	struct mutex events_lock; /* prevents concurrent event processing */
> +
> +	union {
> +		struct virtio_media_cmd_open open;
> +		struct virtio_media_cmd_munmap munmap;
> +	} cmd;
> +
> +	union {
> +		struct virtio_media_resp_open open;
> +		struct virtio_media_resp_munmap munmap;
> +	} resp;


You need DMA alignment padding for these things.

Which one can only see when I reads the actual driver 8 patches down.
Which is why it's not a sensible way to split patches.

A sensible way is to have a driver then add functionality
in logical pieces gradually.


> +
> +	struct mutex vlock; /* serializes command queue access */
> +	wait_queue_head_t wq;
> +};
> +
> +static inline struct virtio_media *
> +to_virtio_media(struct video_device *video_dev)
> +{
> +	return container_of(video_dev, struct virtio_media, video_dev);
> +}
> +
> +/* virtio_media_driver.c */
> +
> +int virtio_media_send_command(struct virtio_media *vv, struct scatterlist **sgs,
> +			      const size_t out_sgs, const size_t in_sgs,
> +			      size_t minimum_resp_len, size_t *resp_len);
> +void virtio_media_process_events(struct virtio_media *vv);
> +
> +/* virtio_media_ioctls.c */
> +
> +long virtio_media_device_ioctl(struct file *file, unsigned int cmd,
> +			       unsigned long arg);
> +extern const struct v4l2_ioctl_ops virtio_media_ioctl_ops;
> +
> +#endif // __VIRTIO_MEDIA_H
> -- 
> 2.55.0.rc0.799.gd6f94ed593-goog