text: /*
   *  linux/fs/char_dev.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   */
  
  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/kdev_t.h>
  #include <linux/slab.h>
  #include <linux/string.h>
  
  #include <linux/major.h>
  #include <linux/errno.h>
  #include <linux/module.h>
  #include <linux/seq_file.h>
  
  #include <linux/kobject.h>
  #include <linux/kobj_map.h>
  #include <linux/cdev.h>
  #include <linux/mutex.h>
  #include <linux/backing-dev.h>
  #include <linux/tty.h>
  
  #include "internal.h"
  
  static struct kobj_map *cdev_map;
  
  static DEFINE_MUTEX(chrdevs_lock);
  
  static struct char_device_struct {
  	struct char_device_struct *next;
  	unsigned int major;
  	unsigned int baseminor;
  	int minorct;
  	char name[64];
  	struct cdev *cdev;		/* will die */
  } *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
  
  /* index in the above */
  static inline int major_to_index(unsigned major)
  {
  	return major % CHRDEV_MAJOR_HASH_SIZE;
  }
  
  #ifdef CONFIG_PROC_FS
  
  void chrdev_show(struct seq_file *f, off_t offset)
  {
  	struct char_device_struct *cd;
  
  	if (offset < CHRDEV_MAJOR_HASH_SIZE) {
  		mutex_lock(&chrdevs_lock);
  		for (cd = chrdevs[offset]; cd; cd = cd->next)
  			seq_printf(f, "%3d %s\n", cd->major, cd->name);
  		mutex_unlock(&chrdevs_lock);
  	}
  }
  
  #endif /* CONFIG_PROC_FS */
  
  /*
   * Register a single major with a specified minor range.
   *
   * If major == 0 this functions will dynamically allocate a major and return
   * its number.
   *
   * If major > 0 this function will attempt to reserve the passed range of
   * minors and will return zero on success.
   *
   * Returns a -ve errno on failure.
   */
  static struct char_device_struct *
  __register_chrdev_region(unsigned int major, unsigned int baseminor,
  			   int minorct, const char *name)
  {
  	struct char_device_struct *cd, **cp;
  	int ret = 0;
  	int i;
  
  	cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
  	if (cd == NULL)
  		return ERR_PTR(-ENOMEM);
  
  	mutex_lock(&chrdevs_lock);
  
  	/* temporary */
  	if (major == 0) {
  		for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
  			if (chrdevs[i] == NULL)
  				break;
  		}
  
  		if (i < CHRDEV_MAJOR_DYN_END)
  			pr_warn("CHRDEV \"%s\" major number %d goes below the dynamic allocation range\n",
  				name, i);
  
  		if (i == 0) {
  			ret = -EBUSY;
  			goto out;
  		}
  		major = i;
  	}
  
  	cd->major = major;
  	cd->baseminor = baseminor;
  	cd->minorct = minorct;
  	strlcpy(cd->name, name, sizeof(cd->name));
  
  	i = major_to_index(major);
  
  	for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
  		if ((*cp)->major > major ||
  		    ((*cp)->major == major &&
  		     (((*cp)->baseminor >= baseminor) ||
  		      ((*cp)->baseminor + (*cp)->minorct > baseminor))))
  			break;
  
  	/* Check for overlapping minor ranges.  */
  	if (*cp && (*cp)->major == major) {
  		int old_min = (*cp)->baseminor;
  		int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
  		int new_min = baseminor;
  		int new_max = baseminor + minorct - 1;
  
  		/* New driver overlaps from the left.  */
  		if (new_max >= old_min && new_max <= old_max) {
  			ret = -EBUSY;
  			goto out;
  		}
  
  		/* New driver overlaps from the right.  */
  		if (new_min <= old_max && new_min >= old_min) {
  			ret = -EBUSY;
  			goto out;
  		}
  	}
  
  	cd->next = *cp;
  	*cp = cd;
  	mutex_unlock(&chrdevs_lock);
  	return cd;
  out:
  	mutex_unlock(&chrdevs_lock);
  	kfree(cd);
  	return ERR_PTR(ret);
  }
  
  static struct char_device_struct *
  __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
  {
  	struct char_device_struct *cd = NULL, **cp;
  	int i = major_to_index(major);
  
  	mutex_lock(&chrdevs_lock);
  	for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
  		if ((*cp)->major == major &&
  		    (*cp)->baseminor == baseminor &&
  		    (*cp)->minorct == minorct)
  			break;
  	if (*cp) {
  		cd = *cp;
  		*cp = cd->next;
  	}
  	mutex_unlock(&chrdevs_lock);
  	return cd;
  }
  
  /**
   * register_chrdev_region() - register a range of device numbers
   * @from: the first in the desired range of device numbers; must include
   *        the major number.
   * @count: the number of consecutive device numbers required
   * @name: the name of the device or driver.
   *
   * Return value is zero on success, a negative error code on failure.
   */
  int register_chrdev_region(dev_t from, unsigned count, const char *name)
  {
  	struct char_device_struct *cd;
  	dev_t to = from + count;
  	dev_t n, next;
  
  	for (n = from; n < to; n = next) {
  		next = MKDEV(MAJOR(n)+1, 0);
  		if (next > to)
  			next = to;
  		cd = __register_chrdev_region(MAJOR(n), MINOR(n),
  			       next - n, name);
  		if (IS_ERR(cd))
  			goto fail;
  	}
  	return 0;
  fail:
  	to = n;
  	for (n = from; n < to; n = next) {
  		next = MKDEV(MAJOR(n)+1, 0);
  		kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
  	}
  	return PTR_ERR(cd);
  }
  
  /**
   * alloc_chrdev_region() - register a range of char device numbers
   * @dev: output parameter for first assigned number
   * @baseminor: first of the requested range of minor numbers
   * @count: the number of minor numbers required
   * @name: the name of the associated device or driver
   *
   * Allocates a range of char device numbers.  The major number will be
   * chosen dynamically, and returned (along with the first minor number)
   * in @dev.  Returns zero or a negative error code.
   */
  int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
  			const char *name)
  {
  	struct char_device_struct *cd;
  	cd = __register_chrdev_region(0, baseminor, count, name);
  	if (IS_ERR(cd))
  		return PTR_ERR(cd);
  	*dev = MKDEV(cd->major, cd->baseminor);
  	return 0;
  }
  
  /**
   * __register_chrdev() - create and register a cdev occupying a range of minors
   * @major: major device number or 0 for dynamic allocation
   * @baseminor: first of the requested range of minor numbers
   * @count: the number of minor numbers required
   * @name: name of this range of devices
   * @fops: file operations associated with this devices
   *
   * If @major == 0 this functions will dynamically allocate a major and return
   * its number.
   *
   * If @major > 0 this function will attempt to reserve a device with the given
   * major number and will return zero on success.
   *
   * Returns a -ve errno on failure.
   *
   * The name of this device has nothing to do with the name of the device in
   * /dev. It only helps to keep track of the different owners of devices. If
   * your module name has only one type of devices it's ok to use e.g. the name
   * of the module here.
   */
  int __register_chrdev(unsigned int major, unsigned int baseminor,
  		      unsigned int count, const char *name,
  		      const struct file_operations *fops)
  {
  	struct char_device_struct *cd;
  	struct cdev *cdev;
  	int err = -ENOMEM;
  
  	cd = __register_chrdev_region(major, baseminor, count, name);
  	if (IS_ERR(cd))
  		return PTR_ERR(cd);
  
  	cdev = cdev_alloc();
  	if (!cdev)
  		goto out2;
  
  	cdev->owner = fops->owner;
  	cdev->ops = fops;
  	kobject_set_name(&cdev->kobj, "%s", name);
  
  	err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
  	if (err)
  		goto out;
  
  	cd->cdev = cdev;
  
  	return major ? 0 : cd->major;
  out:
  	kobject_put(&cdev->kobj);
  out2:
  	kfree(__unregister_chrdev_region(cd->major, baseminor, count));
  	return err;
  }
  
  /**
   * unregister_chrdev_region() - unregister a range of device numbers
   * @from: the first in the range of numbers to unregister
   * @count: the number of device numbers to unregister
   *
   * This function will unregister a range of @count device numbers,
   * starting with @from.  The caller should normally be the one who
   * allocated those numbers in the first place...
   */
  void unregister_chrdev_region(dev_t from, unsigned count)
  {
  	dev_t to = from + count;
  	dev_t n, next;
  
  	for (n = from; n < to; n = next) {
  		next = MKDEV(MAJOR(n)+1, 0);
  		if (next > to)
  			next = to;
  		kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
  	}
  }
  
  /**
   * __unregister_chrdev - unregister and destroy a cdev
   * @major: major device number
   * @baseminor: first of the range of minor numbers
   * @count: the number of minor numbers this cdev is occupying
   * @name: name of this range of devices
   *
   * Unregister and destroy the cdev occupying the region described by
   * @major, @baseminor and @count.  This function undoes what
   * __register_chrdev() did.
   */
  void __unregister_chrdev(unsigned int major, unsigned int baseminor,
  			 unsigned int count, const char *name)
  {
  	struct char_device_struct *cd;
  
  	cd = __unregister_chrdev_region(major, baseminor, count);
  	if (cd && cd->cdev)
  		cdev_del(cd->cdev);
  	kfree(cd);
  }
  
  static DEFINE_SPINLOCK(cdev_lock);
  
  static struct kobject *cdev_get(struct cdev *p)
  {
  	struct module *owner = p->owner;
  	struct kobject *kobj;
  
  	if (owner && !try_module_get(owner))
  		return NULL;
  	kobj = kobject_get(&p->kobj);
  	if (!kobj)
  		module_put(owner);
  	return kobj;
  }
  
  void cdev_put(struct cdev *p)
  {
  	if (p) {
  		struct module *owner = p->owner;
  		kobject_put(&p->kobj);
  		module_put(owner);
  	}
  }
  
  /*
   * Called every time a character special file is opened
   */
  static int chrdev_open(struct inode *inode, struct file *filp)
  {
  	const struct file_operations *fops;
  	struct cdev *p;
  	struct cdev *new = NULL;
  	int ret = 0;
  
  	spin_lock(&cdev_lock);
  	p = inode->i_cdev;
  	if (!p) {
  		struct kobject *kobj;
  		int idx;
  		spin_unlock(&cdev_lock);
  		kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
  		if (!kobj)
  			return -ENXIO;
  		new = container_of(kobj, struct cdev, kobj);
  		spin_lock(&cdev_lock);
  		/* Check i_cdev again in case somebody beat us to it while
  		   we dropped the lock. */
  		p = inode->i_cdev;
  		if (!p) {
  			inode->i_cdev = p = new;
  			list_add(&inode->i_devices, &p->list);
  			new = NULL;
  		} else if (!cdev_get(p))
  			ret = -ENXIO;
  	} else if (!cdev_get(p))
  		ret = -ENXIO;
  	spin_unlock(&cdev_lock);
  	cdev_put(new);
  	if (ret)
  		return ret;
  
  	ret = -ENXIO;
  	fops = fops_get(p->ops);
  	if (!fops)
  		goto out_cdev_put;
  
  	replace_fops(filp, fops);
  	if (filp->f_op->open) {
  		ret = filp->f_op->open(inode, filp);
  		if (ret)
  			goto out_cdev_put;
  	}
  
  	return 0;
  
   out_cdev_put:
  	cdev_put(p);
  	return ret;
  }
  
  void cd_forget(struct inode *inode)
  {
  	spin_lock(&cdev_lock);
  	list_del_init(&inode->i_devices);
  	inode->i_cdev = NULL;
  	inode->i_mapping = &inode->i_data;
  	spin_unlock(&cdev_lock);
  }
  
  static void cdev_purge(struct cdev *cdev)
  {
  	spin_lock(&cdev_lock);
  	while (!list_empty(&cdev->list)) {
  		struct inode *inode;
  		inode = container_of(cdev->list.next, struct inode, i_devices);
  		list_del_init(&inode->i_devices);
  		inode->i_cdev = NULL;
  	}
  	spin_unlock(&cdev_lock);
  }
  
  /*
   * Dummy default file-operations: the only thing this does
   * is contain the open that then fills in the correct operations
   * depending on the special file...
   */
  const struct file_operations def_chr_fops = {
  	.open = chrdev_open,
  	.llseek = noop_llseek,
  };
  
  static struct kobject *exact_match(dev_t dev, int *part, void *data)
  {
  	struct cdev *p = data;
  	return &p->kobj;
  }
  
  static int exact_lock(dev_t dev, void *data)
  {
  	struct cdev *p = data;
  	return cdev_get(p) ? 0 : -1;
  }
  
  /**
   * cdev_add() - add a char device to the system
   * @p: the cdev structure for the device
   * @dev: the first device number for which this device is responsible
   * @count: the number of consecutive minor numbers corresponding to this
   *         device
   *
   * cdev_add() adds the device represented by @p to the system, making it
   * live immediately.  A negative error code is returned on failure.
   */
  int cdev_add(struct cdev *p, dev_t dev, unsigned count)
  {
  	int error;
  
  	p->dev = dev;
  	p->count = count;
  
  	error = kobj_map(cdev_map, dev, count, NULL,
  			 exact_match, exact_lock, p);
  	if (error)
  		return error;
  
  	kobject_get(p->kobj.parent);
  
  	return 0;
  }
  
  static void cdev_unmap(dev_t dev, unsigned count)
  {
  	kobj_unmap(cdev_map, dev, count);
  }
  
  /**
   * cdev_del() - remove a cdev from the system
   * @p: the cdev structure to be removed
   *
   * cdev_del() removes @p from the system, possibly freeing the structure
   * itself.
   */
  void cdev_del(struct cdev *p)
  {
  	cdev_unmap(p->dev, p->count);
  	kobject_put(&p->kobj);
  }
  
  
  static void cdev_default_release(struct kobject *kobj)
  {
  	struct cdev *p = container_of(kobj, struct cdev, kobj);
  	struct kobject *parent = kobj->parent;
  
  	cdev_purge(p);
  	kobject_put(parent);
  }
  
  static void cdev_dynamic_release(struct kobject *kobj)
  {
  	struct cdev *p = container_of(kobj, struct cdev, kobj);
  	struct kobject *parent = kobj->parent;
  
  	cdev_purge(p);
  	kfree(p);
  	kobject_put(parent);
  }
  
  static struct kobj_type ktype_cdev_default = {
  	.release	= cdev_default_release,
  };
  
  static struct kobj_type ktype_cdev_dynamic = {
  	.release	= cdev_dynamic_release,
  };
  
  /**
   * cdev_alloc() - allocate a cdev structure
   *
   * Allocates and returns a cdev structure, or NULL on failure.
   */
  struct cdev *cdev_alloc(void)
  {
  	struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
  	if (p) {
  		INIT_LIST_HEAD(&p->list);
  		kobject_init(&p->kobj, &ktype_cdev_dynamic);
  	}
  	return p;
  }
  
  /**
   * cdev_init() - initialize a cdev structure
   * @cdev: the structure to initialize
   * @fops: the file_operations for this device
   *
   * Initializes @cdev, remembering @fops, making it ready to add to the
   * system with cdev_add().
   */
  void cdev_init(struct cdev *cdev, const struct file_operations *fops)
  {
  	memset(cdev, 0, sizeof *cdev);
  	INIT_LIST_HEAD(&cdev->list);
  	kobject_init(&cdev->kobj, &ktype_cdev_default);
  	cdev->ops = fops;
  }
  
  static struct kobject *base_probe(dev_t dev, int *part, void *data)
  {
  	if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
  		/* Make old-style 2.4 aliases work */
  		request_module("char-major-%d", MAJOR(dev));
  	return NULL;
  }
  
  void __init chrdev_init(void)
  {
  	cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
  }
  
  
  /* Let modules do char dev stuff */
  EXPORT_SYMBOL(register_chrdev_region);
  EXPORT_SYMBOL(unregister_chrdev_region);
  EXPORT_SYMBOL(alloc_chrdev_region);
  EXPORT_SYMBOL(cdev_init);
  EXPORT_SYMBOL(cdev_alloc);
  EXPORT_SYMBOL(cdev_del);
  EXPORT_SYMBOL(cdev_add);
  EXPORT_SYMBOL(__register_chrdev);
  EXPORT_SYMBOL(__unregister_chrdev);
  