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 copied mostly verbatim from video/v4l2-dev.c.
Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
---
drivers/media/Makefile | 8 +-
drivers/media/media-devnode.c | 479 +++++++++++++++++++++++++++++++++++++++++
include/media/media-devnode.h | 97 +++++++++
3 files changed, 582 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..53f618b
--- /dev/null
+++ b/drivers/media/media-devnode.c
@@ -0,0 +1,479 @@
+/*
+ * 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 struct media_devnode *media_devnodes[MEDIA_NUM_DEVICES];
+static DEFINE_MUTEX(media_devnode_lock);
+static DECLARE_BITMAP(devnode_nums[MEDIA_TYPE_MAX], MEDIA_NUM_DEVICES);
+
+/* Device node utility functions */
+
+/* Note: these utility functions all assume that type is in the range
+ [0, MEDIA_TYPE_MAX-1]. */
+
+/* Return the bitmap corresponding to type. */
+static inline unsigned long *devnode_bits(int type)
+{
+ return devnode_nums[type];
+}
+
+/* Mark device node number mdev->num as used */
+static inline void devnode_set(struct media_devnode *mdev)
+{
+ set_bit(mdev->num, devnode_bits(mdev->type));
+}
+
+/* Mark device node number mdev->num as unused */
+static inline void devnode_clear(struct media_devnode *mdev)
+{
+ clear_bit(mdev->num, devnode_bits(mdev->type));
+}
+
+/* Try to find a free device node number in the range [from, to> */
+static inline int devnode_find(struct media_devnode *mdev, int from, int to)
+{
+ return find_next_zero_bit(devnode_bits(mdev->type), to, from);
+}
+
+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);
+}
+
+/* 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);
+ if (media_devnodes[mdev->minor] != mdev) {
+ mutex_unlock(&media_devnode_lock);
+ /* should not happen */
+ WARN_ON(1);
+ return;
+ }
+
+ /* Free up this device for reuse */
+ media_devnodes[mdev->minor] = NULL;
+
+ /* Delete the cdev on this minor as well */
+ cdev_del(mdev->cdev);
+ /* Just in case some driver tries to access this from the release()
+ * callback.
+ */
+ mdev->cdev = NULL;
+
+ /* Mark device node number as free */
+ devnode_clear(mdev);
+
+ 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,
+};
+
+struct media_devnode *media_devnode_data(struct file *file)
+{
+ return media_devnodes[iminor(file->f_path.dentry->d_inode)];
+}
+EXPORT_SYMBOL(media_devnode_data);
+
+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);
+ int ret = -ENOTTY;
+
+ /* Allow ioctl to continue even if the device was unregistered.
+ Things like dequeueing buffers might still be useful. */
+ if (mdev->fops->unlocked_ioctl)
+ ret = mdev->fops->unlocked_ioctl(filp, cmd, arg);
+ else if (mdev->fops->ioctl) {
+ lock_kernel();
+ ret = mdev->fops->ioctl(filp, cmd, arg);
+ unlock_kernel();
+ }
+
+ return ret;
+}
+
+#ifdef CONFIG_MMU
+#define media_get_unmapped_area NULL
+#else
+static unsigned long media_get_unmapped_area(struct file *filp,
+ unsigned long addr, unsigned long len, unsigned long pgoff,
+ unsigned long flags)
+{
+ struct media_devnode *mdev = media_devnode_data(filp);
+
+ if (!mdev->fops->get_unmapped_area)
+ return -ENOSYS;
+ if (!media_devnode_is_registered(mdev))
+ return -ENODEV;
+ return mdev->fops->get_unmapped_area(filp, addr, len, pgoff, flags);
+}
+#endif
+
+static int media_mmap(struct file *filp, struct vm_area_struct *vm)
+{
+ struct media_devnode *mdev = media_devnode_data(filp);
+
+ if (!mdev->fops->mmap || !media_devnode_is_registered(mdev))
+ return -ENODEV;
+ return mdev->fops->mmap(filp, vm);
+}
+
+/* Override for the open function */
+static int media_open(struct inode *inode, struct file *filp)
+{
+ struct media_devnode *mdev;
+ int ret = 0;
+
+ /* Check if the media device is available */
+ mutex_lock(&media_devnode_lock);
+ mdev = media_devnode_data(filp);
+ /* 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)) {
+ 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);
+
+ /* decrease the refcount in case of an error */
+ if (ret)
+ media_put(mdev);
+ return ret;
+}
+
+/* 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);
+ return ret;
+}
+
+static const struct file_operations media_devnode_fops = {
+ .owner = THIS_MODULE,
+ .read = media_read,
+ .write = media_write,
+ .open = media_open,
+ .get_unmapped_area = media_get_unmapped_area,
+ .mmap = media_mmap,
+ .unlocked_ioctl = media_ioctl,
+#ifdef CONFIG_COMPAT
+/* .compat_ioctl = media_compat_ioctl32, */
+#endif
+ .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
+ * @type: type of device node to register
+ *
+ * The registration code assigns minor numbers and device node numbers based
+ * on the requested type and registers the new device node with the kernel. An
+ * error is returned if no free minor or device node number could be found, or
+ * if the registration of the device node failed.
+ *
+ * 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.
+ *
+ * Valid types are
+ *
+ * %MEDIA_TYPE_DEVICE - A media device
+ */
+int __must_check media_devnode_register(struct media_devnode *mdev, int type)
+{
+ const char *name_base;
+ int minor_offset = 0;
+ int minor_cnt = MEDIA_NUM_DEVICES;
+ void *priv;
+ int ret;
+ int nr;
+ int i;
+
+ /* Part 1: check device type. */
+ name_base = media_devnode_type_name(type);
+ if (name_base == NULL) {
+ printk(KERN_ERR "%s called with unknown type: %d\n",
+ __func__, type);
+ return -EINVAL;
+ }
+
+ mdev->type = type;
+ mdev->cdev = NULL;
+
+ /* Part 2: find a free minor and device node number. */
+
+ /* Pick a device node number */
+ mutex_lock(&media_devnode_lock);
+ nr = devnode_find(mdev, 0, minor_cnt);
+ if (nr == minor_cnt) {
+ printk(KERN_ERR "could not get a free device node number\n");
+ mutex_unlock(&media_devnode_lock);
+ return -ENFILE;
+ }
+
+ /* The device node number and minor numbers are independent, so we just
+ * find the first free minor number.
+ */
+ for (i = 0; i < MEDIA_NUM_DEVICES; i++)
+ if (media_devnodes[i] == NULL)
+ break;
+ if (i == MEDIA_NUM_DEVICES) {
+ mutex_unlock(&media_devnode_lock);
+ printk(KERN_ERR "could not get a free minor\n");
+ return -ENFILE;
+ }
+
+ mdev->minor = i + minor_offset;
+ mdev->num = nr;
+ devnode_set(mdev);
+
+ /* Should not happen since we thought this minor was free */
+ WARN_ON(media_devnodes[mdev->minor] != NULL);
+ mutex_unlock(&media_devnode_lock);
+
+ /* Part 3: Initialize the character device */
+ mdev->cdev = cdev_alloc();
+ if (mdev->cdev == NULL) {
+ ret = -ENOMEM;
+ goto cleanup;
+ }
+ mdev->cdev->ops = &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__);
+ kfree(mdev->cdev);
+ mdev->cdev = NULL;
+ goto cleanup;
+ }
+
+ /* Part 4: register the device with sysfs
+ *
+ * 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);
+ mdev->dev.class = &media_class;
+ mdev->dev.devt = MKDEV(MAJOR(media_dev_t), mdev->minor);
+ if (mdev->parent)
+ mdev->dev.parent = mdev->parent;
+ dev_set_name(&mdev->dev, "%s%d", name_base, mdev->num);
+ ret = device_register(&mdev->dev);
+ if (ret < 0) {
+ printk(KERN_ERR "%s: device_register failed\n", __func__);
+ goto cleanup;
+ }
+ /* Register the release callback that will be called when the last
+ reference to the device goes away. */
+ mdev->dev.release = media_devnode_release;
+
+ /* Part 5: Activate this minor. The char device can now be used. */
+ set_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
+ mutex_lock(&media_devnode_lock);
+ media_devnodes[mdev->minor] = mdev;
+ mutex_unlock(&media_devnode_lock);
+ return 0;
+
+cleanup:
+ mutex_lock(&media_devnode_lock);
+ if (mdev->cdev)
+ cdev_del(mdev->cdev);
+ devnode_clear(mdev);
+ 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);
+}
+
+const char *media_devnode_type_name(int type)
+{
+ switch (type) {
+ case MEDIA_TYPE_DEVICE:
+ return "media";
+ default:
+ return NULL;
+ }
+}
+
+/*
+ * 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..85c890f
--- /dev/null
+++ b/include/media/media-devnode.h
@@ -0,0 +1,97 @@
+/*
+ * 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>
+
+/* Media device node type. */
+#define MEDIA_TYPE_DEVICE 0
+#define MEDIA_TYPE_MAX 1
+
+/*
+ * 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);
+ 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
+ * @type: node type, one of the MEDIA_TYPE_* constants
+ * @minor: device node minor number
+ * @num: device node 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.
+ */
+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 type;
+
+ int minor;
+ u16 num;
+ 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, int type);
+void media_devnode_unregister(struct media_devnode *mdev);
+
+const char *media_devnode_type_name(int type);
+struct media_devnode *media_devnode_data(struct file *file);
+
+static inline int media_devnode_is_registered(struct media_devnode *mdev)
+{
+ return test_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
+}
+
+#endif /* _MEDIA_DEVNODE_H */
--
1.7.1
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