On Wednesday 21 July 2010 16:35:26 Laurent Pinchart wrote:
> The media_devnode structure provides support for registering and
> unregistering character devices using a dynamic major number. Reference
> counting is handled internally, making device drivers easier to write
> without having to solve the open/disconnect race condition issue over
> and over again.
>
> The code is based on video/v4l2-dev.c.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
> drivers/media/Makefile | 8 +-
> drivers/media/media-devnode.c | 339 +++++++++++++++++++++++++++++++++++++++++
> include/media/media-devnode.h | 91 +++++++++++
> 3 files changed, 436 insertions(+), 2 deletions(-)
> create mode 100644 drivers/media/media-devnode.c
> create mode 100644 include/media/media-devnode.h
>
> diff --git a/drivers/media/Makefile b/drivers/media/Makefile
> index 499b081..c1b5938 100644
> --- a/drivers/media/Makefile
> +++ b/drivers/media/Makefile
> @@ -2,7 +2,11 @@
> # Makefile for the kernel multimedia device drivers.
> #
>
> +media-objs := media-devnode.o
> +
> +obj-$(CONFIG_MEDIA_SUPPORT) += media.o
> +
> obj-y += common/ IR/ video/
>
> -obj-$(CONFIG_VIDEO_DEV) += radio/
> -obj-$(CONFIG_DVB_CORE) += dvb/
> +obj-$(CONFIG_VIDEO_DEV) += radio/
> +obj-$(CONFIG_DVB_CORE) += dvb/
> diff --git a/drivers/media/media-devnode.c b/drivers/media/media-devnode.c
> new file mode 100644
> index 0000000..fa300f8
> --- /dev/null
> +++ b/drivers/media/media-devnode.c
> @@ -0,0 +1,339 @@
> +/*
> + * Media device node
> + *
> + * Generic media device node infrastructure to register and unregister
> + * character devices using a dynamic major number and proper reference
> + * counting.
> + *
> + * Copyright 2010 Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> + *
> + * Based on drivers/media/video/v4l2_dev.c code authored by
> + *
> + * Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx> (version 2)
> + * Alan Cox, <alan@xxxxxxxxxxxxxxxxxxx> (version 1)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version
> + * 2 of the License, or (at your option) any later version.
> + *
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/kmod.h>
> +#include <linux/slab.h>
> +#include <linux/mm.h>
> +#include <linux/smp_lock.h>
> +#include <linux/string.h>
> +#include <linux/types.h>
> +#include <linux/uaccess.h>
> +#include <asm/system.h>
> +
> +#include <media/media-devnode.h>
> +
> +#define MEDIA_NUM_DEVICES 256
> +#define MEDIA_NAME "media"
> +
> +static dev_t media_dev_t;
> +
> +/*
> + * sysfs stuff
> + */
> +
> +static ssize_t show_name(struct device *cd,
> + struct device_attribute *attr, char *buf)
> +{
> + struct media_devnode *mdev = to_media_devnode(cd);
> +
> + return sprintf(buf, "%.*s\n", (int)sizeof(mdev->name), mdev->name);
> +}
> +
> +static struct device_attribute media_devnode_attrs[] = {
> + __ATTR(name, S_IRUGO, show_name, NULL),
> + __ATTR_NULL
> +};
> +
> +/*
> + * Active devices
> + */
> +static DEFINE_MUTEX(media_devnode_lock);
I don't think this lock is actually needed. The bit operations are already
atomic, so we can do without this lock.
> +static DECLARE_BITMAP(media_devnode_nums, MEDIA_NUM_DEVICES);
> +
> +static inline void media_get(struct media_devnode *mdev)
> +{
> + get_device(&mdev->dev);
> +}
> +
> +static inline void media_put(struct media_devnode *mdev)
> +{
> + put_device(&mdev->dev);
> +}
These functions are used quite rarely. I'd remove these inlines and just
call get/put_device directly.
> +
> +/* Called when the last user of the media device exits. */
> +static void media_devnode_release(struct device *cd)
> +{
> + struct media_devnode *mdev = to_media_devnode(cd);
> +
> + mutex_lock(&media_devnode_lock);
> +
> + /* Delete the cdev on this minor as well */
> + cdev_del(&mdev->cdev);
> +
> + /* Mark device node number as free */
> + clear_bit(mdev->minor, media_devnode_nums);
> +
> + mutex_unlock(&media_devnode_lock);
> +
> + /* Release media_devnode and perform other cleanups as needed. */
> + if (mdev->release)
> + mdev->release(mdev);
> +}
> +
> +static struct class media_class = {
> + .name = MEDIA_NAME,
> + .dev_attrs = media_devnode_attrs,
> +};
> +
> +static ssize_t media_read(struct file *filp, char __user *buf,
> + size_t sz, loff_t *off)
> +{
> + struct media_devnode *mdev = media_devnode_data(filp);
> +
> + if (!mdev->fops->read)
> + return -EINVAL;
> + if (!media_devnode_is_registered(mdev))
> + return -EIO;
> + return mdev->fops->read(filp, buf, sz, off);
> +}
> +
> +static ssize_t media_write(struct file *filp, const char __user *buf,
> + size_t sz, loff_t *off)
> +{
> + struct media_devnode *mdev = media_devnode_data(filp);
> +
> + if (!mdev->fops->write)
> + return -EINVAL;
> + if (!media_devnode_is_registered(mdev))
> + return -EIO;
> + return mdev->fops->write(filp, buf, sz, off);
> +}
> +
> +static unsigned int media_poll(struct file *filp,
> + struct poll_table_struct *poll)
> +{
> + struct media_devnode *mdev = media_devnode_data(filp);
> +
> + if (!mdev->fops->poll || !media_devnode_is_registered(mdev))
> + return DEFAULT_POLLMASK;
> + return mdev->fops->poll(filp, poll);
> +}
> +
> +static long media_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> +{
> + struct media_devnode *mdev = media_devnode_data(filp);
> +
> + if (!media_devnode_is_registered(mdev))
> + return -EIO;
> +
> + if (!mdev->fops->unlocked_ioctl)
> + return -ENOTTY;
These two if's should be swapper (just like in media_read and write).
> +
> + return mdev->fops->unlocked_ioctl(filp, cmd, arg);
> +}
> +
> +/* Override for the open function */
> +static int media_open(struct inode *inode, struct file *filp)
> +{
> + struct media_devnode *mdev;
> + int ret;
> +
> + /* Check if the media device is available */
> + mutex_lock(&media_devnode_lock);
> + mdev = container_of(inode->i_cdev, struct media_devnode, cdev);
> + /* return ENODEV if the media device has been removed
> + already or if it is not registered anymore. */
> + if (mdev == NULL || !media_devnode_is_registered(mdev)) {
mdev can never be NULL.
> + mutex_unlock(&media_devnode_lock);
> + return -ENODEV;
> + }
> + /* and increase the device refcount */
> + media_get(mdev);
> + mutex_unlock(&media_devnode_lock);
> + if (mdev->fops->open) {
> + ret = mdev->fops->open(filp);
> + if (ret) {
> + media_put(mdev);
> + return ret;
> + }
> + }
> +
> + filp->private_data = mdev;
> + return 0;
> +}
> +
> +/* Override for the release function */
> +static int media_release(struct inode *inode, struct file *filp)
> +{
> + struct media_devnode *mdev = media_devnode_data(filp);
> + int ret = 0;
> +
> + if (mdev->fops->release)
> + mdev->fops->release(filp);
> +
> + /* decrease the refcount unconditionally since the release()
> + return value is ignored. */
> + media_put(mdev);
> + filp->private_data = NULL;
> + return ret;
> +}
> +
> +static const struct file_operations media_devnode_fops = {
> + .owner = THIS_MODULE,
> + .read = media_read,
> + .write = media_write,
> + .open = media_open,
> + .unlocked_ioctl = media_ioctl,
> + .release = media_release,
> + .poll = media_poll,
> + .llseek = no_llseek,
> +};
> +
> +/**
> + * media_devnode_register - register a media device node
> + * @mdev: media device node structure we want to register
> + *
> + * The registration code assigns minor numbers and registers the new device node
> + * with the kernel. An error is returned if no free minor number can be found,
> + * or if the registration of the device node fails.
> + *
> + * Zero is returned on success.
> + *
> + * Note that if the media_devnode_register call fails, the release() callback of
> + * the media_devnode structure is *not* called, so the caller is responsible for
> + * freeing any data.
> + */
> +int __must_check media_devnode_register(struct media_devnode *mdev)
> +{
> + void *priv;
> + int minor;
> + int ret;
> +
> + /* Part 1: find a free minor number */
> + mutex_lock(&media_devnode_lock);
> + minor = find_next_zero_bit(media_devnode_nums, 0, MEDIA_NUM_DEVICES);
When media_devnode_lock is removed we can't use find_next_zero_bit anymore.
Instead, we have to loop over all bits and call test_and_set_bit() to ensure
atomicity.
> + if (minor == MEDIA_NUM_DEVICES) {
> + printk(KERN_ERR "could not get a free minor\n");
> + mutex_unlock(&media_devnode_lock);
> + return -ENFILE;
> + }
> +
> + set_bit(mdev->minor, media_devnode_nums);
> + mdev->minor = minor;
> +
> + mutex_unlock(&media_devnode_lock);
> +
> + /* Part 2: Initialize and register the character device */
> + cdev_init(&mdev->cdev, &media_devnode_fops);
> + mdev->cdev.owner = mdev->fops->owner;
> +
> + ret = cdev_add(&mdev->cdev, MKDEV(MAJOR(media_dev_t), mdev->minor), 1);
> + if (ret < 0) {
> + printk(KERN_ERR "%s: cdev_add failed\n", __func__);
> + goto error;
> + }
> +
> + /* Part 3: register the media device
> + *
> + * Zeroing struct device will clear the device's drvdata, so make a
> + * copy and put it back.
> + */
> + priv = dev_get_drvdata(&mdev->dev);
> + memset(&mdev->dev, 0, sizeof(mdev->dev));
> + dev_set_drvdata(&mdev->dev, priv);
Don't zero mdev->dev. We should assume that mdev has been zeroed by the caller.
This construct is actually a bug in v4l2-dev.c. I've seen patches that fixed it,
but I don't know the status of those patches. The problem is that dev_set_drvdata
these days allocates memory. So if dev_set_drvdata was called before this
function, then this construct will leak a bit of memory.
I would just remove this and require that mdev was initialized correctly
when it was allocated.
> + mdev->dev.class = &media_class;
> + mdev->dev.devt = MKDEV(MAJOR(media_dev_t), mdev->minor);
> + mdev->dev.release = media_devnode_release;
> + if (mdev->parent)
> + mdev->dev.parent = mdev->parent;
> + dev_set_name(&mdev->dev, "media%d", mdev->minor);
Wouldn't mediactlX be a better name? Just plain 'media' is awfully general.
> + ret = device_register(&mdev->dev);
> + if (ret < 0) {
> + printk(KERN_ERR "%s: device_register failed\n", __func__);
> + goto error;
> + }
> +
> + /* Part 4: Activate this minor. The char device can now be used. */
> + set_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
> +
> + return 0;
> +
> +error:
> + cdev_del(&mdev->cdev);
> + mutex_lock(&media_devnode_lock);
> + clear_bit(mdev->minor, media_devnode_nums);
> + mutex_unlock(&media_devnode_lock);
> + return ret;
> +}
> +
> +/**
> + * media_devnode_unregister - unregister a media device node
> + * @mdev: the device node to unregister
> + *
> + * This unregisters the passed device. Future open calls will be met with
> + * errors.
> + *
> + * This function can safely be called if the device node has never been
> + * registered or has already been unregistered.
> + */
> +void media_devnode_unregister(struct media_devnode *mdev)
> +{
> + /* Check if mdev was ever registered at all */
> + if (!media_devnode_is_registered(mdev))
> + return;
> +
> + mutex_lock(&media_devnode_lock);
> + clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
> + mutex_unlock(&media_devnode_lock);
> + device_unregister(&mdev->dev);
> +}
> +
> +/*
> + * Initialise media for linux
> + */
> +static int __init media_devnode_init(void)
> +{
> + int ret;
> +
> + printk(KERN_INFO "Linux media interface: v0.10\n");
> + ret = alloc_chrdev_region(&media_dev_t, 0, MEDIA_NUM_DEVICES,
> + MEDIA_NAME);
> + if (ret < 0) {
> + printk(KERN_WARNING "media: unable to allcoate major\n");
> + return ret;
> + }
> +
> + ret = class_register(&media_class);
> + if (ret < 0) {
> + unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
> + printk(KERN_WARNING "media: class_register failed\n");
> + return -EIO;
> + }
> +
> + return 0;
> +}
> +
> +static void __exit media_devnode_exit(void)
> +{
> + class_unregister(&media_class);
> + unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
> +}
> +
> +module_init(media_devnode_init)
> +module_exit(media_devnode_exit)
> +
> +MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("Device node registration for media drivers");
> +MODULE_LICENSE("GPL");
> diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h
> new file mode 100644
> index 0000000..5c8f682
> --- /dev/null
> +++ b/include/media/media-devnode.h
> @@ -0,0 +1,91 @@
> +/*
> + * Media device node handling
> + *
> + * Copyright (C) 2010 Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> + *
> + * Common functions for media-related drivers to register and unregister media
> + * device nodes.
> + */
> +#ifndef _MEDIA_DEVNODE_H
> +#define _MEDIA_DEVNODE_H
> +
> +#include <linux/poll.h>
> +#include <linux/fs.h>
> +#include <linux/device.h>
> +#include <linux/cdev.h>
> +
> +/*
> + * Flag to mark the media_devnode struct as registered. Drivers must not touch
> + * this flag directly, it will be set and cleared by media_devnode_register and
> + * media_devnode_unregister.
> + */
> +#define MEDIA_FLAG_REGISTERED 0
> +
> +struct media_file_operations {
> + struct module *owner;
> + ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
> + ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
> + unsigned int (*poll) (struct file *, struct poll_table_struct *);
> + long (*ioctl) (struct file *, unsigned int, unsigned long);
I think you forgot to remove the ioctl, mmap and get_unmapped_area ops from this
struct.
> + long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
> + unsigned long (*get_unmapped_area) (struct file *, unsigned long,
> + unsigned long, unsigned long, unsigned long);
> + int (*mmap) (struct file *, struct vm_area_struct *);
> + int (*open) (struct file *);
> + int (*release) (struct file *);
> +};
> +
> +/**
> + * struct media_devnode - Media device node
> + * @parent: parent device
> + * @name: media device node name
> + * @minor: device node minor number
> + * @flags: flags, combination of the MEDIA_FLAG_* constants
> + *
> + * This structure represents a media-related device node.
> + *
> + * The @parent is a physical device. It must be set by core or device drivers
> + * before registering the node.
> + *
> + * @name is a descriptive name exported through sysfs. It doesn't have to be
> + * unique.
> + *
> + * The device node number @num is used to create the kobject name and thus
> + * serves as a hint to udev when creating the device node.
'num' no longer exists.
> + */
> +struct media_devnode {
> + /* device ops */
> + const struct media_file_operations *fops;
> +
> + /* sysfs */
> + struct device dev; /* v4l device */
> + struct cdev cdev; /* character device */
> + struct device *parent; /* device parent */
> +
> + /* device info */
> + char name[32];
> +
> + int minor;
> + unsigned long flags; /* Use bitops to access flags */
> +
> + /* callbacks */
> + void (*release)(struct media_devnode *mdev);
> +};
> +
> +/* dev to media_devnode */
> +#define to_media_devnode(cd) container_of(cd, struct media_devnode, dev)
> +
> +int __must_check media_devnode_register(struct media_devnode *mdev);
> +void media_devnode_unregister(struct media_devnode *mdev);
> +
> +static inline struct media_devnode *media_devnode_data(struct file *filp)
> +{
> + return filp->private_data;
> +}
> +
> +static inline int media_devnode_is_registered(struct media_devnode *mdev)
> +{
> + return test_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
> +}
> +
> +#endif /* _MEDIA_DEVNODE_H */
>
Regards,
Hans
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG, part of Cisco
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