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![Dmitry Torokhov](/assets/img/avatar_default.png)
In certain cases (for example when a cdev structure is embedded into another object whose lifetime is controlled by a separate kobject) it is beneficial to tie lifetime of another object to the lifetime of character device so that related object is not freed until after char_dev object is freed. To achieve this let's pin kobject's parent when doing cdev_add() and unpin when last reference to cdev structure is being released. Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
591 lines
14 KiB
C
591 lines
14 KiB
C
/*
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* linux/fs/char_dev.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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*/
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/kdev_t.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include <linux/major.h>
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#include <linux/errno.h>
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#include <linux/module.h>
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#include <linux/seq_file.h>
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#include <linux/kobject.h>
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#include <linux/kobj_map.h>
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#include <linux/cdev.h>
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#include <linux/mutex.h>
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#include <linux/backing-dev.h>
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#include <linux/tty.h>
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#include "internal.h"
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/*
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* capabilities for /dev/mem, /dev/kmem and similar directly mappable character
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* devices
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* - permits shared-mmap for read, write and/or exec
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* - does not permit private mmap in NOMMU mode (can't do COW)
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* - no readahead or I/O queue unplugging required
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*/
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struct backing_dev_info directly_mappable_cdev_bdi = {
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.name = "char",
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.capabilities = (
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#ifdef CONFIG_MMU
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/* permit private copies of the data to be taken */
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BDI_CAP_MAP_COPY |
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#endif
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/* permit direct mmap, for read, write or exec */
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BDI_CAP_MAP_DIRECT |
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BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP |
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/* no writeback happens */
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BDI_CAP_NO_ACCT_AND_WRITEBACK),
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};
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static struct kobj_map *cdev_map;
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static DEFINE_MUTEX(chrdevs_lock);
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static struct char_device_struct {
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struct char_device_struct *next;
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unsigned int major;
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unsigned int baseminor;
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int minorct;
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char name[64];
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struct cdev *cdev; /* will die */
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} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
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/* index in the above */
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static inline int major_to_index(unsigned major)
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{
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return major % CHRDEV_MAJOR_HASH_SIZE;
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}
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#ifdef CONFIG_PROC_FS
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void chrdev_show(struct seq_file *f, off_t offset)
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{
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struct char_device_struct *cd;
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if (offset < CHRDEV_MAJOR_HASH_SIZE) {
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mutex_lock(&chrdevs_lock);
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for (cd = chrdevs[offset]; cd; cd = cd->next)
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seq_printf(f, "%3d %s\n", cd->major, cd->name);
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mutex_unlock(&chrdevs_lock);
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}
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}
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#endif /* CONFIG_PROC_FS */
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/*
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* Register a single major with a specified minor range.
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*
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* If major == 0 this functions will dynamically allocate a major and return
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* its number.
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*
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* If major > 0 this function will attempt to reserve the passed range of
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* minors and will return zero on success.
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*
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* Returns a -ve errno on failure.
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*/
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static struct char_device_struct *
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__register_chrdev_region(unsigned int major, unsigned int baseminor,
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int minorct, const char *name)
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{
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struct char_device_struct *cd, **cp;
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int ret = 0;
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int i;
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cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
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if (cd == NULL)
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return ERR_PTR(-ENOMEM);
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mutex_lock(&chrdevs_lock);
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/* temporary */
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if (major == 0) {
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for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
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if (chrdevs[i] == NULL)
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break;
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}
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if (i == 0) {
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ret = -EBUSY;
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goto out;
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}
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major = i;
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ret = major;
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}
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cd->major = major;
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cd->baseminor = baseminor;
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cd->minorct = minorct;
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strlcpy(cd->name, name, sizeof(cd->name));
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i = major_to_index(major);
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for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
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if ((*cp)->major > major ||
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((*cp)->major == major &&
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(((*cp)->baseminor >= baseminor) ||
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((*cp)->baseminor + (*cp)->minorct > baseminor))))
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break;
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/* Check for overlapping minor ranges. */
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if (*cp && (*cp)->major == major) {
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int old_min = (*cp)->baseminor;
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int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
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int new_min = baseminor;
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int new_max = baseminor + minorct - 1;
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/* New driver overlaps from the left. */
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if (new_max >= old_min && new_max <= old_max) {
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ret = -EBUSY;
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goto out;
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}
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/* New driver overlaps from the right. */
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if (new_min <= old_max && new_min >= old_min) {
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ret = -EBUSY;
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goto out;
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}
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}
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cd->next = *cp;
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*cp = cd;
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mutex_unlock(&chrdevs_lock);
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return cd;
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out:
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mutex_unlock(&chrdevs_lock);
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kfree(cd);
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return ERR_PTR(ret);
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}
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static struct char_device_struct *
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__unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
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{
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struct char_device_struct *cd = NULL, **cp;
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int i = major_to_index(major);
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mutex_lock(&chrdevs_lock);
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for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
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if ((*cp)->major == major &&
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(*cp)->baseminor == baseminor &&
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(*cp)->minorct == minorct)
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break;
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if (*cp) {
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cd = *cp;
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*cp = cd->next;
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}
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mutex_unlock(&chrdevs_lock);
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return cd;
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}
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/**
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* register_chrdev_region() - register a range of device numbers
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* @from: the first in the desired range of device numbers; must include
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* the major number.
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* @count: the number of consecutive device numbers required
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* @name: the name of the device or driver.
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*
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* Return value is zero on success, a negative error code on failure.
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*/
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int register_chrdev_region(dev_t from, unsigned count, const char *name)
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{
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struct char_device_struct *cd;
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dev_t to = from + count;
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dev_t n, next;
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for (n = from; n < to; n = next) {
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next = MKDEV(MAJOR(n)+1, 0);
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if (next > to)
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next = to;
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cd = __register_chrdev_region(MAJOR(n), MINOR(n),
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next - n, name);
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if (IS_ERR(cd))
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goto fail;
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}
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return 0;
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fail:
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to = n;
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for (n = from; n < to; n = next) {
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next = MKDEV(MAJOR(n)+1, 0);
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kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
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}
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return PTR_ERR(cd);
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}
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/**
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* alloc_chrdev_region() - register a range of char device numbers
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* @dev: output parameter for first assigned number
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* @baseminor: first of the requested range of minor numbers
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* @count: the number of minor numbers required
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* @name: the name of the associated device or driver
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*
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* Allocates a range of char device numbers. The major number will be
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* chosen dynamically, and returned (along with the first minor number)
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* in @dev. Returns zero or a negative error code.
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*/
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int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
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const char *name)
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{
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struct char_device_struct *cd;
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cd = __register_chrdev_region(0, baseminor, count, name);
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if (IS_ERR(cd))
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return PTR_ERR(cd);
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*dev = MKDEV(cd->major, cd->baseminor);
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return 0;
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}
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/**
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* __register_chrdev() - create and register a cdev occupying a range of minors
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* @major: major device number or 0 for dynamic allocation
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* @baseminor: first of the requested range of minor numbers
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* @count: the number of minor numbers required
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* @name: name of this range of devices
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* @fops: file operations associated with this devices
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*
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* If @major == 0 this functions will dynamically allocate a major and return
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* its number.
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*
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* If @major > 0 this function will attempt to reserve a device with the given
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* major number and will return zero on success.
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*
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* Returns a -ve errno on failure.
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*
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* The name of this device has nothing to do with the name of the device in
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* /dev. It only helps to keep track of the different owners of devices. If
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* your module name has only one type of devices it's ok to use e.g. the name
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* of the module here.
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*/
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int __register_chrdev(unsigned int major, unsigned int baseminor,
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unsigned int count, const char *name,
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const struct file_operations *fops)
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{
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struct char_device_struct *cd;
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struct cdev *cdev;
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int err = -ENOMEM;
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cd = __register_chrdev_region(major, baseminor, count, name);
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if (IS_ERR(cd))
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return PTR_ERR(cd);
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cdev = cdev_alloc();
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if (!cdev)
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goto out2;
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cdev->owner = fops->owner;
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cdev->ops = fops;
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kobject_set_name(&cdev->kobj, "%s", name);
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err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
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if (err)
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goto out;
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cd->cdev = cdev;
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return major ? 0 : cd->major;
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out:
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kobject_put(&cdev->kobj);
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out2:
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kfree(__unregister_chrdev_region(cd->major, baseminor, count));
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return err;
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}
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/**
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* unregister_chrdev_region() - return a range of device numbers
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* @from: the first in the range of numbers to unregister
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* @count: the number of device numbers to unregister
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*
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* This function will unregister a range of @count device numbers,
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* starting with @from. The caller should normally be the one who
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* allocated those numbers in the first place...
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*/
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void unregister_chrdev_region(dev_t from, unsigned count)
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{
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dev_t to = from + count;
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dev_t n, next;
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for (n = from; n < to; n = next) {
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next = MKDEV(MAJOR(n)+1, 0);
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if (next > to)
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next = to;
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kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
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}
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}
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/**
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* __unregister_chrdev - unregister and destroy a cdev
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* @major: major device number
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* @baseminor: first of the range of minor numbers
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* @count: the number of minor numbers this cdev is occupying
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* @name: name of this range of devices
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*
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* Unregister and destroy the cdev occupying the region described by
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* @major, @baseminor and @count. This function undoes what
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* __register_chrdev() did.
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*/
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void __unregister_chrdev(unsigned int major, unsigned int baseminor,
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unsigned int count, const char *name)
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{
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struct char_device_struct *cd;
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cd = __unregister_chrdev_region(major, baseminor, count);
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if (cd && cd->cdev)
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cdev_del(cd->cdev);
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kfree(cd);
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}
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static DEFINE_SPINLOCK(cdev_lock);
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static struct kobject *cdev_get(struct cdev *p)
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{
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struct module *owner = p->owner;
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struct kobject *kobj;
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if (owner && !try_module_get(owner))
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return NULL;
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kobj = kobject_get(&p->kobj);
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if (!kobj)
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module_put(owner);
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return kobj;
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}
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void cdev_put(struct cdev *p)
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{
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if (p) {
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struct module *owner = p->owner;
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kobject_put(&p->kobj);
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module_put(owner);
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}
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}
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/*
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* Called every time a character special file is opened
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*/
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static int chrdev_open(struct inode *inode, struct file *filp)
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{
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struct cdev *p;
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struct cdev *new = NULL;
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int ret = 0;
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spin_lock(&cdev_lock);
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p = inode->i_cdev;
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if (!p) {
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struct kobject *kobj;
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int idx;
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spin_unlock(&cdev_lock);
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kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
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if (!kobj)
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return -ENXIO;
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new = container_of(kobj, struct cdev, kobj);
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spin_lock(&cdev_lock);
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/* Check i_cdev again in case somebody beat us to it while
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we dropped the lock. */
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p = inode->i_cdev;
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if (!p) {
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inode->i_cdev = p = new;
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list_add(&inode->i_devices, &p->list);
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new = NULL;
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} else if (!cdev_get(p))
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ret = -ENXIO;
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} else if (!cdev_get(p))
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ret = -ENXIO;
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spin_unlock(&cdev_lock);
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cdev_put(new);
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if (ret)
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return ret;
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ret = -ENXIO;
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filp->f_op = fops_get(p->ops);
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if (!filp->f_op)
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goto out_cdev_put;
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if (filp->f_op->open) {
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ret = filp->f_op->open(inode, filp);
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if (ret)
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goto out_cdev_put;
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}
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return 0;
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out_cdev_put:
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cdev_put(p);
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return ret;
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}
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void cd_forget(struct inode *inode)
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{
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spin_lock(&cdev_lock);
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list_del_init(&inode->i_devices);
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inode->i_cdev = NULL;
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spin_unlock(&cdev_lock);
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}
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static void cdev_purge(struct cdev *cdev)
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{
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spin_lock(&cdev_lock);
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while (!list_empty(&cdev->list)) {
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struct inode *inode;
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inode = container_of(cdev->list.next, struct inode, i_devices);
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list_del_init(&inode->i_devices);
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inode->i_cdev = NULL;
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}
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spin_unlock(&cdev_lock);
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}
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/*
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* Dummy default file-operations: the only thing this does
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* is contain the open that then fills in the correct operations
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* depending on the special file...
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*/
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const struct file_operations def_chr_fops = {
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.open = chrdev_open,
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.llseek = noop_llseek,
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};
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static struct kobject *exact_match(dev_t dev, int *part, void *data)
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{
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struct cdev *p = data;
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return &p->kobj;
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}
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static int exact_lock(dev_t dev, void *data)
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{
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struct cdev *p = data;
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return cdev_get(p) ? 0 : -1;
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}
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/**
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* cdev_add() - add a char device to the system
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* @p: the cdev structure for the device
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* @dev: the first device number for which this device is responsible
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* @count: the number of consecutive minor numbers corresponding to this
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* device
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*
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* cdev_add() adds the device represented by @p to the system, making it
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* live immediately. A negative error code is returned on failure.
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*/
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int cdev_add(struct cdev *p, dev_t dev, unsigned count)
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{
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int error;
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p->dev = dev;
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p->count = count;
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error = kobj_map(cdev_map, dev, count, NULL,
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exact_match, exact_lock, p);
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if (error)
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return error;
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kobject_get(p->kobj.parent);
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return 0;
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}
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static void cdev_unmap(dev_t dev, unsigned count)
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{
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kobj_unmap(cdev_map, dev, count);
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}
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/**
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* cdev_del() - remove a cdev from the system
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* @p: the cdev structure to be removed
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*
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* cdev_del() removes @p from the system, possibly freeing the structure
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* itself.
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*/
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void cdev_del(struct cdev *p)
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{
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cdev_unmap(p->dev, p->count);
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kobject_put(&p->kobj);
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}
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static void cdev_default_release(struct kobject *kobj)
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{
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struct cdev *p = container_of(kobj, struct cdev, kobj);
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struct kobject *parent = kobj->parent;
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cdev_purge(p);
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kobject_put(parent);
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}
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static void cdev_dynamic_release(struct kobject *kobj)
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{
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struct cdev *p = container_of(kobj, struct cdev, kobj);
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struct kobject *parent = kobj->parent;
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cdev_purge(p);
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kfree(p);
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kobject_put(parent);
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}
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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);
|
|
bdi_init(&directly_mappable_cdev_bdi);
|
|
}
|
|
|
|
|
|
/* 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);
|
|
EXPORT_SYMBOL(directly_mappable_cdev_bdi);
|