Re: [RFCv4 01/21] media: add request API core and UAPI

[Hans Verkuil <hverkuil@xs4all.nl>]

On 02/20/18 05:44, Alexandre Courbot wrote:
> The request API provides a way to group buffers and device parameters
> into units of work to be queued and executed. This patch introduces the
> UAPI and core framework.
> 
> This patch is based on the previous work by Laurent Pinchart. The core
> has changed considerably, but the UAPI is mostly untouched.
> 
> Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
> ---
>  drivers/media/Kconfig              |   3 +
>  drivers/media/Makefile             |   6 +
>  drivers/media/media-request.c      | 341 ++++++++++++++++++++++++++++
>  include/media/media-request.h      | 349 +++++++++++++++++++++++++++++
>  include/uapi/linux/media-request.h |  37 +++
>  5 files changed, 736 insertions(+)
>  create mode 100644 drivers/media/media-request.c
>  create mode 100644 include/media/media-request.h
>  create mode 100644 include/uapi/linux/media-request.h
> 
> diff --git a/drivers/media/Kconfig b/drivers/media/Kconfig
> index 145e12bfb819..db30fc9547d2 100644
> --- a/drivers/media/Kconfig
> +++ b/drivers/media/Kconfig
> @@ -130,6 +130,9 @@ config VIDEO_V4L2_SUBDEV_API
>  
>  	  This API is mostly used by camera interfaces in embedded platforms.
>  
> +config MEDIA_REQUEST_API
> +	tristate
> +
>  source "drivers/media/v4l2-core/Kconfig"
>  
>  #
> diff --git a/drivers/media/Makefile b/drivers/media/Makefile
> index 594b462ddf0e..03c0a39ad344 100644
> --- a/drivers/media/Makefile
> +++ b/drivers/media/Makefile
> @@ -5,6 +5,12 @@
>  
>  media-objs	:= media-device.o media-devnode.o media-entity.o
>  
> +#
> +# Request API support comes as its own module since it can be used by
> +# both media and video devices
> +#
> +obj-$(CONFIG_MEDIA_REQUEST_API) += media-request.o
> +
>  #
>  # I2C drivers should come before other drivers, otherwise they'll fail
>  # when compiled as builtin drivers
> diff --git a/drivers/media/media-request.c b/drivers/media/media-request.c
> new file mode 100644
> index 000000000000..b88362028561
> --- /dev/null
> +++ b/drivers/media/media-request.c
> @@ -0,0 +1,341 @@
> +/*
> + * Request base implementation
> + *
> + * Copyright (C) 2018, The Chromium OS Authors.  All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/anon_inodes.h>
> +#include <linux/fs.h>
> +#include <linux/file.h>
> +#include <linux/list.h>
> +#include <linux/device.h>
> +#include <linux/media-request.h>
> +#include <linux/module.h>
> +#include <linux/poll.h>
> +#include <linux/slab.h>
> +
> +#include <media/media-request.h>
> +
> +const struct file_operations request_fops;
> +
> +static const char * const media_request_states[] __maybe_unused = {

Why 'maybe_unused'?

> +	"IDLE",
> +	"SUBMITTED",
> +	"COMPLETED",
> +	"INVALID",

I don't like to yell. I prefer "Idle", "Submitted", etc.

> +};
> +
> +struct media_request *media_request_get(struct media_request *req)
> +{
> +	get_file(req->file);
> +	return req;
> +}
> +EXPORT_SYMBOL_GPL(media_request_get);
> +
> +struct media_request *media_request_get_from_fd(int fd)
> +{
> +	struct file *f;
> +
> +	f = fget(fd);
> +	if (!f)
> +		return NULL;
> +
> +	/* Not a request FD? */
> +	if (f->f_op != &request_fops) {
> +		fput(f);
> +		return NULL;
> +	}
> +
> +	return f->private_data;
> +}
> +EXPORT_SYMBOL_GPL(media_request_get_from_fd);
> +
> +void media_request_put(struct media_request *req)
> +{
> +	if (WARN_ON(req == NULL))
> +		return;
> +
> +	fput(req->file);
> +}
> +EXPORT_SYMBOL_GPL(media_request_put);
> +
> +struct media_request_entity_data *
> +media_request_get_entity_data(struct media_request *req,
> +			      struct media_request_entity *entity)
> +{
> +	struct media_request_entity_data *data;
> +
> +	/* First check that this entity is valid for this request at all */
> +	if (!req->mgr->ops->entity_valid(req, entity))
> +		return ERR_PTR(-EINVAL);
> +
> +	mutex_lock(&req->lock);
> +
> +	/* Lookup whether we already have entity data */
> +	list_for_each_entry(data, &req->data, list) {
> +		if (data->entity == entity)
> +			goto out;
> +	}
> +
> +	/* No entity data found, let's create it */
> +	data = entity->ops->data_alloc(req, entity);
> +	if (IS_ERR(data))
> +		goto out;
> +
> +	data->entity = entity;
> +	list_add_tail(&data->list, &req->data);
> +
> +out:
> +	mutex_unlock(&req->lock);
> +
> +	return data;
> +}
> +EXPORT_SYMBOL_GPL(media_request_get_entity_data);
> +
> +static unsigned int media_request_poll(struct file *file, poll_table *wait)
> +{
> +	struct media_request *req = file->private_data;
> +
> +	poll_wait(file, &req->complete_wait, wait);
> +
> +	if (req->state == MEDIA_REQUEST_STATE_COMPLETED)
> +		return POLLIN | POLLRDNORM;
> +
> +	return 0;
> +}
> +
> +static int media_request_release(struct inode *inode, struct file *filp)
> +{
> +	struct media_request *req = filp->private_data;
> +
> +	if (req == NULL)
> +		return 0;
> +
> +	req->mgr->ops->release(req);
> +	return 0;
> +}
> +
> +static long media_request_ioctl_submit(struct media_request *req)
> +{
> +	mutex_lock(&req->lock);
> +
> +	if (req->state != MEDIA_REQUEST_STATE_IDLE) {
> +		dev_warn(req->mgr->dev, "cannot submit request in state %s\n",
> +			 media_request_states[req->state]);
> +		mutex_unlock(&req->lock);
> +		return -EINVAL;
> +	}
> +
> +	req->state = MEDIA_REQUEST_STATE_SUBMITTED;
> +
> +	/*
> +	 * Nothing can change our state when we are submitted - no need to keep
> +	 * holding that lock.
> +	 */
> +	mutex_unlock(&req->lock);
> +
> +	/* Keep a reference to the request until it is completed */
> +	media_request_get(req);
> +
> +	return req->mgr->ops->submit(req);

What happens if submit() returns an error? I would expect that the state goes
back to IDLE and the reference is put().

> +}
> +
> +static long media_request_ioctl_reinit(struct media_request *req)
> +{
> +	struct media_request_entity_data *data, *next;
> +        LIST_HEAD(to_delete);

Weird indentation.

> +
> +	mutex_lock(&req->lock);
> +
> +	if (req->state == MEDIA_REQUEST_STATE_SUBMITTED) {
> +		dev_warn(req->mgr->dev,
> +			"%s: unable to reinit submitted request\n", __func__);
> +		mutex_unlock(&req->lock);
> +		return -EINVAL;
> +	}
> +
> +	/* delete all entity data */
> +	list_for_each_entry_safe(data, next, &req->data, list) {
> +		list_del(&data->list);
> +                list_add(&data->list, &to_delete);

Strange indentation.

You can also use list_move(&data->list, &to_delete).

> +	}
> +
> +	/* reinitialize request to idle state */
> +	req->state = MEDIA_REQUEST_STATE_IDLE;
> +
> +	mutex_unlock(&req->lock);
> +
> +        list_for_each_entry_safe(data, next, &to_delete, list)

Again strange indentation. Not sure what's going on with that.
I'll ignore it going forward.

> +		data->entity->ops->data_free(data);
> +
> +	return 0;
> +}
> +
> +#define MEDIA_REQUEST_IOC(__cmd, func)					\
> +	[_IOC_NR(MEDIA_REQUEST_IOC_##__cmd) - 0x80] = {			\
> +		.cmd = MEDIA_REQUEST_IOC_##__cmd,			\
> +		.fn = func,						\
> +	}
> +
> +struct media_request_ioctl_info {
> +	unsigned int cmd;
> +	long (*fn)(struct media_request *req);
> +};
> +
> +static const struct media_request_ioctl_info ioctl_info[] = {
> +	MEDIA_REQUEST_IOC(SUBMIT, media_request_ioctl_submit),
> +	MEDIA_REQUEST_IOC(REINIT, media_request_ioctl_reinit),

There are only two ioctls, so there is really no need for the
MEDIA_REQUEST_IOC define. Just keep it simple.

> +};
> +
> +static long media_request_ioctl(struct file *filp, unsigned int cmd,
> +				unsigned long __arg)
> +{
> +	struct media_request *req = filp->private_data;
> +	const struct media_request_ioctl_info *info;
> +
> +	if ((_IOC_NR(cmd) < 0x80) ||

Why start the ioctl number at 0x80? Why not just 0?
It avoids all this hassle with the 0x80 offset.

> +	     _IOC_NR(cmd) >= 0x80 + ARRAY_SIZE(ioctl_info) ||
> +	     ioctl_info[_IOC_NR(cmd) - 0x80].cmd != cmd)
> +		return -ENOIOCTLCMD;
> +
> +	info = &ioctl_info[_IOC_NR(cmd) - 0x80];
> +
> +	return info->fn(req);
> +}
> +
> +const struct file_operations request_fops = {
> +	.owner = THIS_MODULE,
> +	.poll = media_request_poll,
> +	.release = media_request_release,
> +	.unlocked_ioctl = media_request_ioctl,
> +};
> +
> +static void media_request_complete(struct media_request *req)
> +{
> +	struct device *dev = req->mgr->dev;
> +
> +	mutex_lock(&req->lock);
> +
> +	if (WARN_ON(req->state != MEDIA_REQUEST_STATE_SUBMITTED)) {
> +		dev_warn(dev, "can't complete request in state %s\n",
> +			media_request_states[req->state]);
> +		mutex_unlock(&req->lock);
> +		return;
> +	}
> +
> +	req->state = MEDIA_REQUEST_STATE_COMPLETED;
> +
> +	wake_up_interruptible(&req->complete_wait);
> +
> +	mutex_unlock(&req->lock);
> +
> +	/* Release the reference acquired when we submitted the request */
> +	media_request_put(req);
> +}
> +
> +void media_request_entity_complete(struct media_request *req,
> +				   struct media_request_entity *completed)
> +{
> +	struct media_request_entity_data *data;
> +	int cpt = 0;
> +
> +	list_for_each_entry(data, &req->data, list) {
> +		if (data->entity == completed)
> +			data->completed = true;
> +		if (!data->completed)

This can be 'else if'.

> +			++cpt;
> +	}
> +
> +	if (cpt == 0)
> +		media_request_complete(req);
> +}
> +EXPORT_SYMBOL_GPL(media_request_entity_complete);
> +
> +long media_request_ioctl_new(struct media_request_mgr *mgr,
> +			     struct media_request_new *new)
> +{
> +	struct media_request *req;
> +	int err;
> +	int fd;
> +
> +	/* User only wants to check the availability of requests? */
> +	if (new->flags & MEDIA_REQUEST_FLAG_TEST)
> +		return 0;
> +
> +	fd = get_unused_fd_flags(O_CLOEXEC);
> +	if (fd < 0)
> +		return fd;
> +
> +	req = mgr->ops->alloc(mgr);
> +	if (IS_ERR(req)) {
> +		err = PTR_ERR(req);
> +		goto out_fd;
> +	}
> +
> +	req->file = anon_inode_getfile("request", &request_fops, req,
> +				       O_CLOEXEC);
> +	if (IS_ERR(req->file)) {
> +		err = PTR_ERR(req->file);
> +		mgr->ops->release(req);
> +		goto out_fd;
> +	}
> +
> +	fd_install(fd, req->file);
> +	new->fd = fd;
> +
> +	return 0;
> +
> +out_fd:
> +	put_unused_fd(fd);
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(media_request_ioctl_new);
> +
> +void media_request_entity_init(struct media_request_entity *entity,
> +			       enum media_request_entity_type type,
> +			       const struct media_request_entity_ops *ops)
> +{
> +	entity->type = type;
> +	entity->ops = ops;
> +}
> +EXPORT_SYMBOL_GPL(media_request_entity_init);
> +
> +void media_request_mgr_init(struct media_request_mgr *mgr, struct device *dev,
> +			    const struct media_request_ops *ops)
> +{
> +	mgr->dev = dev;
> +	mutex_init(&mgr->mutex);
> +	INIT_LIST_HEAD(&mgr->requests);
> +	mgr->ops = ops;
> +}
> +EXPORT_SYMBOL_GPL(media_request_mgr_init);
> +
> +void media_request_mgr_free(struct media_request_mgr *mgr)
> +{
> +	struct device *dev = mgr->dev;
> +
> +	/* Just a sanity check - we should have no remaining requests */
> +	while (!list_empty(&mgr->requests)) {
> +		struct media_request *req;
> +
> +		req = list_first_entry(&mgr->requests, typeof(*req), list);
> +		dev_warn(dev,
> +			"%s: request still referenced, deleting forcibly!\n",
> +			__func__);
> +		mgr->ops->release(req);
> +	}
> +}
> +EXPORT_SYMBOL_GPL(media_request_mgr_free);
> +
> +MODULE_AUTHOR("Alexandre Courbot <acourbot@chromium.org>");
> +MODULE_DESCRIPTION("Core support for media request API");
> +MODULE_LICENSE("GPL");
> diff --git a/include/media/media-request.h b/include/media/media-request.h
> new file mode 100644
> index 000000000000..110dcdc1099f
> --- /dev/null
> +++ b/include/media/media-request.h
> @@ -0,0 +1,349 @@
> +/*
> + * Media requests.
> + *
> + * Copyright (C) 2018, The Chromium OS Authors.  All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#ifndef _MEDIA_REQUEST_H
> +#define _MEDIA_REQUEST_H
> +
> +struct media_request;
> +struct media_request_entity;
> +struct media_request_entity_data;
> +struct media_request_mgr;
> +struct media_request_new;
> +
> +#include <linux/kconfig.h>
> +
> +enum media_request_state {
> +	MEDIA_REQUEST_STATE_IDLE,
> +	MEDIA_REQUEST_STATE_SUBMITTED,
> +	MEDIA_REQUEST_STATE_COMPLETED,
> +	MEDIA_REQUEST_STATE_INVALID,
> +};
> +
> +#if IS_ENABLED(CONFIG_MEDIA_REQUEST_API)
> +
> +#include <linux/kref.h>
> +#include <linux/list.h>
> +#include <linux/notifier.h>
> +#include <linux/wait.h>
> +
> +/**
> + * struct media_request_entity_ops - request entity operations
> + *
> + * @data_alloc:	allocate memory to store that entity's relevant state
> + * @data_free:	free state previously allocated with data_alloc
> + * @submit:	perform all required actions to be ready to process that request
> + */
> +struct media_request_entity_ops {
> +	struct media_request_entity_data *
> +		(*data_alloc)(struct media_request *req,
> +			      struct media_request_entity *entity);
> +	void (*data_free)(struct media_request_entity_data *data);
> +	int (*submit)(struct media_request *req,
> +		      struct media_request_entity_data *data);
> +};
> +
> +/**
> + * enum media_request_entity_type - describe type of an entity
> + *
> + * This type lets us know the upper kind of a struct media_request_entity
> + * instance.
> + *
> + * @MEDIA_REQUEST_ENTITY_TYPE_V4L2:	instance can be upcasted to
> + * 					v4l2_request_entity
> + * @MEDIA_REQUEST_ENTITY_TYPE_MC:	instance can be updated to
> + * 					mc_request_entity
> + *
> + */
> +enum media_request_entity_type {
> +	MEDIA_REQUEST_ENTITY_TYPE_V4L2,
> +	MEDIA_REQUEST_ENTITY_TYPE_MC,
> +};
> +
> +/**
> + * struct media_request_entity - request entity base structure
> + *
> + * @type:	type of entity, indicating which upcast is safe to perform
> + * @ops:	operations that this entity can perform
> + *
> + * This structure is supposed to be embedded into a larger structure
> + * better representing the specifics of the instance (e.g. v4l2_request_entity
> + * for controlling V4L2 devices).
> + *
> + */
> +struct media_request_entity {
> +	enum media_request_entity_type type;
> +	const struct media_request_entity_ops *ops;
> +};
> +
> +/**
> + * media_request_entity_init() - initialize a request entity's base properties
> + *
> + * @entity:	entity to initialize
> + * @type:	type of this entity
> + * @ops:	operations that this entity will perform
> + */
> +void media_request_entity_init(struct media_request_entity *entity,
> +			       enum media_request_entity_type type,
> +			       const struct media_request_entity_ops *ops);
> +
> +/**
> + * struct media_request_entity_data - per-entity request data
> + *
> + * @request:	request instance this data belongs to
> + * @entity:	entity that stores data here
> + * @list:	entry in media_request::data
> + * @completed:	whether this entity has completed its part of the request
> + *
> + * Base structure used to store request state data. To be extended by actual
> + * implementation.
> + *
> + */
> +struct media_request_entity_data {
> +	struct media_request *request;
> +	struct media_request_entity *entity;
> +	struct list_head list;
> +	bool completed;
> +};
> +
> +/**
> + * struct media_request - Media request base structure
> + *
> + * @mgr:	manager this request belongs to
> + * @file:	used to export FDs to user-space and reference count
> + * @list:	entry in the media_request_mgr::requests list
> + * @lock:	protects following members against concurrent accesses
> + * @state:	current state of the request
> + * @data:	per-entity data list
> + * @complete_wait:	wait queue that signals once the request has completed
> + */
> +struct media_request {
> +	struct media_request_mgr *mgr;
> +	struct file *file;
> +	struct list_head list;
> +
> +	struct mutex lock;
> +	enum media_request_state state;
> +	struct list_head data;
> +	wait_queue_head_t complete_wait;
> +};
> +
> +/**
> + * media_request_get() - increment the reference counter of a request
> + *
> + * The calling context must call media_request_put() once it does not need
> + * the reference to the request anymore.
> + *
> + * Returns the request that has been passed as argument.
> + *
> + * @req:	request to acquire a reference of
> + */
> +struct media_request *media_request_get(struct media_request *req);
> +
> +/**
> + * media_request_get_from_fd() - lookup request by fd and acquire a reference.
> + *
> + * Look a request up from its fd, acquire a reference and return a pointer to
> + * the request. As for media_request_get(), media_request_put() must be called
> + * once the reference is not used anymore.
> + *
> + * @req:	request to lookup and acquire.
> + *
> + */
> +struct media_request *media_request_get_from_fd(int fd);
> +
> +/**
> + * media_request_put() - decrement the reference counter of a request
> + *
> + * Mirror function of media_request_get() and media_request_get_from_fd(). Will
> + * free the request if this was the last valid reference.
> + *
> + * @req:	request to release.
> + */
> +void media_request_put(struct media_request *req);
> +
> +/**
> + * media_request_lock() - prevent concurrent access to that request
> + *
> + * @req:	request to lock
> + */
> +static inline void media_request_lock(struct media_request *req)
> +{
> +	mutex_lock(&req->lock);
> +}
> +
> +/**
> + * media_request_unlock() - release previously acquired request lock
> + *
> + * @req:	request to release
> + */
> +static inline void media_request_unlock(struct media_request *req)
> +{
> +	mutex_unlock(&req->lock);
> +}
> +
> +/**
> + * media_request_get_state() - get the state of a request
> + *
> + * @req:	request which state we are interested in
> + *
> + * The request lock should always be acquired when confirming this value
> + * to avoid race conditions.
> + *
> + */
> +static inline enum media_request_state
> +media_request_get_state(struct media_request *req)
> +{
> +	return req->state;
> +}
> +
> +/**
> + * media_request_get_entity_data() - get per-entity data for a request
> + * @req:	request to get entity data from
> + * @entity:	entity to get data of
> + *
> + * Search and return the entity data associated associated to the request. If no
> + * such data exists, it is allocated as per the entity operations.
> + *
> + * Returns the per-entity data, or an error code if a problem happened. -EINVAL
> + * means that data for the entity already existed, but has been allocated under
> + * a different cookie.
> + */
> +struct media_request_entity_data *
> +media_request_get_entity_data(struct media_request *req,
> +			      struct media_request_entity *entity);
> +
> +/**
> + * media_request_entity_complete() - to be invoked when an entity completes its
> + *				     part of the request
> + *
> + * @req:	request which has completed
> + * @completed:	entity that has completed
> + */
> +void media_request_entity_complete(struct media_request *req,
> +				   struct media_request_entity *completed);
> +
> +/**
> + * media_request_ioctl_new() - process a NEW_REQUEST ioctl
> + *
> + * @mgr:	request manager from which to allocate the request
> + * @new:	media_request_new structure to be passed back to user-space
> + *
> + * This function is a helper to be called by actual handlers of *_NEW_REQUEST
> + * ioctls.
> + */
> +long media_request_ioctl_new(struct media_request_mgr *mgr,
> +			     struct media_request_new *new);
> +
> +/**
> + * struct media_request_ops - request operations
> + *
> + * @alloc:	allocate a request
> + * @release:	free a previously allocated request
> + * @entity_valid:	returns whether a given entity is valid for that request
> + * @submit:	allow the request to be processed
> + *
> + * This structure allows to specialize requests to a specific scope. For
> + * instance, requests obtained from a V4L2 device node should only be able to
> + * control that device. On the other hand, requests created from a media
> + * controller node will be able to control all the devices managed by this
> + * controller, and may want to implement some form of synchronization between
> + * them.
> + */
> +struct media_request_ops {
> +	struct media_request *(*alloc)(struct media_request_mgr *mgr);
> +	void (*release)(struct media_request *req);
> +	bool (*entity_valid)(const struct media_request *req,
> +			     const struct media_request_entity *entity);
> +	int (*submit)(struct media_request *req);
> +};
> +
> +/**
> + * struct media_request_mgr - requests manager
> + *
> + * @dev:	device owning this manager
> + * @ops:	implementation of the manager
> + * @mutex:	protects the requests list_head
> + * @requests:	list of alive requests produced by this manager
> + *
> + * This structure is mainly responsible for allocating requests. Although it is
> + * not strictly required for that purpose, having it allows us to account for
> + * all requests created by a given device, and to make sure they are all
> + * discarded by the time the device is destroyed.
> + */
> +struct media_request_mgr {
> +	struct device *dev;
> +	const struct media_request_ops *ops;
> +
> +	struct mutex mutex;
> +	struct list_head requests;
> +};
> +
> +/**
> + * media_request_mgr_init() - initialize a request manager.
> + *
> + * @mgr:	manager to initialize
> + */
> +void media_request_mgr_init(struct media_request_mgr *mgr, struct device *dev,
> +			    const struct media_request_ops *ops);
> +
> +/**
> + * media_request_mgr_free() - free a media manager
> + *
> + * This should only be called when all requests produced by this manager
> + * has been destroyed. Will warn if that is not the case.
> + */
> +void media_request_mgr_free(struct media_request_mgr *mgr);
> +
> +#else /* CONFIG_MEDIA_REQUEST_API */
> +
> +static inline void media_request_entity_complete(struct media_request *req,
> +					 struct media_request_entity *completed)
> +{
> +}
> +
> +static inline struct media_request_entity_data *
> +media_request_get_entity_data(struct media_request *req,
> +			      struct media_request_entity *entity)
> +{
> +	return ERR_PTR(-ENOTSUPP);
> +}
> +
> +static inline long media_request_ioctl_new(struct media_request_mgr *mgr,
> +					   struct media_request_new *new)
> +{
> +	return -ENOTTY;
> +}
> +
> +static inline void media_request_put(struct media_request *req)
> +{
> +}
> +
> +static inline void media_request_lock(struct media_request *req)
> +{
> +}
> +
> +static inline void media_request_unlock(struct media_request *req)
> +{
> +}
> +
> +static inline enum media_request_state
> +media_request_get_state(struct media_request *req)
> +{
> +	return MEDIA_REQUEST_STATE_INVALID;
> +}
> +
> +#endif /* CONFIG_MEDIA_REQUEST_API */
> +
> +#endif
> diff --git a/include/uapi/linux/media-request.h b/include/uapi/linux/media-request.h
> new file mode 100644
> index 000000000000..5d30f731a442
> --- /dev/null
> +++ b/include/uapi/linux/media-request.h
> @@ -0,0 +1,37 @@
> +/*
> + * Media requests UAPI
> + *
> + * Copyright (C) 2018, The Chromium OS Authors.  All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#ifndef __LINUX_MEDIA_REQUEST_H
> +#define __LINUX_MEDIA_REQUEST_H
> +
> +#ifndef __KERNEL__
> +#include <stdint.h>
> +#endif
> +#include <linux/ioctl.h>
> +#include <linux/types.h>
> +#include <linux/version.h>
> +
> +/* Only check that requests can be used, do not allocate */
> +#define MEDIA_REQUEST_FLAG_TEST			0x00000001
> +
> +struct media_request_new {
> +	__u32 flags;
> +	__s32 fd;
> +} __attribute__ ((packed));
> +
> +#define MEDIA_REQUEST_IOC_SUBMIT	  _IO('|',  128)
> +#define MEDIA_REQUEST_IOC_REINIT	  _IO('|',  129)
> +
> +#endif
> 

I need to think a bit more on this internal API, so I might come back
to this patch for more comments.

Regards,

	Hans