misc.c

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/*
 * linux/drivers/char/misc.c
 *
 * Generic misc open routine by Johan Myreen
 *
 * Based on code from Linus
 *
 * Teemu Rantanen's Microsoft Busmouse support and Derrick Cole's
 *   changes incorporated into 0.97pl4
 *   by Peter Cervasio (pete%[email protected]) (08SEP92)
 *   See busmouse.c for particulars.
 *
 * Made things a lot mode modular - easy to compile in just one or two
 * of the misc drivers, as they are now completely independent. Linus.
 *
 * Support for loadable modules. 8-Sep-95 Philip Blundell <[email protected]>
 *
 * Fixed a failing symbol register to free the device registration
 *      Alan Cox <[email protected]> 21-Jan-96
 *
 * Dynamic minors and /proc/mice by Alessandro Rubini. 26-Mar-96
 *
 * Renamed to misc and miscdevice to be more accurate. Alan Cox 26-Mar-96
 *
 * Handling of mouse minor numbers for kerneld:
 *  Idea by Jacques Gelinas <[email protected]>,
 *  adapted by Bjorn Ekwall <[email protected]>
 *  corrected by Alan Cox <[email protected]>
 *
 * Changes for kmod (from kerneld):
 *  Cyrus Durgin <[email protected]>
 *
 * Added devfs support. Richard Gooch <[email protected]>  10-Jan-1998
 */

#include <linux/module.h>

#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>

/*
 * Head entry for the doubly linked miscdevice list
 */
static LIST_HEAD(misc_list);
static DEFINE_MUTEX(misc_mtx);

/*
 * Assigned numbers, used for dynamic minors
 */
#define DYNAMIC_MINORS 64 /* like dynamic majors */
static DECLARE_BITMAP(misc_minors, DYNAMIC_MINORS);

#ifdef CONFIG_PROC_FS
static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
{
    mutex_lock(&misc_mtx);
    return seq_list_start(&misc_list, *pos);
}

static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
    return seq_list_next(v, &misc_list, pos);
}

static void misc_seq_stop(struct seq_file *seq, void *v)
{
    mutex_unlock(&misc_mtx);
}

static int misc_seq_show(struct seq_file *seq, void *v)
{
    const struct miscdevice *p = list_entry(v, struct miscdevice, list);

    seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
    return 0;
}


static const struct seq_operations misc_seq_ops = {
    .start = misc_seq_start,
    .next  = misc_seq_next,
    .stop  = misc_seq_stop,
    .show  = misc_seq_show,
};

static int misc_seq_open(struct inode *inode, struct file *file)
{
    return seq_open(file, &misc_seq_ops);
}

static const struct file_operations misc_proc_fops = {
    .owner   = THIS_MODULE,
    .open    = misc_seq_open,
    .read    = seq_read,
    .llseek  = seq_lseek,
    .release = seq_release,
};
#endif

static int misc_open(struct inode * inode, struct file * file)
{
    int minor = iminor(inode);
    struct miscdevice *c;
    int err = -ENODEV;
    const struct file_operations *old_fops, *new_fops = NULL;

    mutex_lock(&misc_mtx);
    
    list_for_each_entry(c, &misc_list, list) {
        if (c->minor == minor) {
            new_fops = fops_get(c->fops);       
            break;
        }
    }
        
    if (!new_fops) {
        mutex_unlock(&misc_mtx);
        request_module("char-major-%d-%d", MISC_MAJOR, minor);
        mutex_lock(&misc_mtx);

        list_for_each_entry(c, &misc_list, list) {
            if (c->minor == minor) {
                new_fops = fops_get(c->fops);
                break;
            }
        }
        if (!new_fops)
            goto fail;
    }

    err = 0;
    old_fops = file->f_op;
    file->f_op = new_fops;
    if (file->f_op->open) {
        file->private_data = c;
        err=file->f_op->open(inode,file);
        if (err) {
            fops_put(file->f_op);
            file->f_op = fops_get(old_fops);
        }
    }
    fops_put(old_fops);
fail:
    mutex_unlock(&misc_mtx);
    return err;
}

static struct class *misc_class;

static const struct file_operations misc_fops = {
    .owner      = THIS_MODULE,
    .open       = misc_open,
    .llseek     = noop_llseek,
};

int misc_register(struct miscdevice * misc)
{
    struct miscdevice *c;
    dev_t dev;
    int err = 0;

    INIT_LIST_HEAD(&misc->list);

    mutex_lock(&misc_mtx);
    list_for_each_entry(c, &misc_list, list) {
        if (c->minor == misc->minor) {
            mutex_unlock(&misc_mtx);
            return -EBUSY;
        }
    }

    if (misc->minor == MISC_DYNAMIC_MINOR) {
        int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
        if (i >= DYNAMIC_MINORS) {
            mutex_unlock(&misc_mtx);
            return -EBUSY;
        }
        misc->minor = DYNAMIC_MINORS - i - 1;
        set_bit(i, misc_minors);
    }

    dev = MKDEV(MISC_MAJOR, misc->minor);

    misc->this_device = device_create(misc_class, misc->parent, dev,
                      misc, "%s", misc->name);
    if (IS_ERR(misc->this_device)) {
        int i = DYNAMIC_MINORS - misc->minor - 1;
        if (i < DYNAMIC_MINORS && i >= 0)
            clear_bit(i, misc_minors);
        err = PTR_ERR(misc->this_device);
        goto out;
    }

    /*
     * Add it to the front, so that later devices can "override"
     * earlier defaults
     */
    list_add(&misc->list, &misc_list);
 out:
    mutex_unlock(&misc_mtx);
    return err;
}

int misc_deregister(struct miscdevice *misc)
{
    int i = DYNAMIC_MINORS - misc->minor - 1;

    if (WARN_ON(list_empty(&misc->list)))
        return -EINVAL;

    mutex_lock(&misc_mtx);
    list_del(&misc->list);
    device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
    if (i < DYNAMIC_MINORS && i >= 0)
        clear_bit(i, misc_minors);
    mutex_unlock(&misc_mtx);
    return 0;
}

EXPORT_SYMBOL(misc_register);
EXPORT_SYMBOL(misc_deregister);

static char *misc_devnode(struct device *dev, umode_t *mode)
{
    struct miscdevice *c = dev_get_drvdata(dev);

    if (mode && c->mode)
        *mode = c->mode;
    if (c->nodename)
        return kstrdup(c->nodename, GFP_KERNEL);
    return NULL;
}

static int __init misc_init(void)
{
    int err;

#ifdef CONFIG_PROC_FS
    proc_create("misc", 0, NULL, &misc_proc_fops);
#endif
    misc_class = class_create(THIS_MODULE, "misc");
    err = PTR_ERR(misc_class);
    if (IS_ERR(misc_class))
        goto fail_remove;

    err = -EIO;
    if (register_chrdev(MISC_MAJOR,"misc",&misc_fops))
        goto fail_printk;
    misc_class->devnode = misc_devnode;
    return 0;

fail_printk:
    printk("unable to get major %d for misc devices\n", MISC_MAJOR);
    class_destroy(misc_class);
fail_remove:
    remove_proc_entry("misc", NULL);
    return err;
}
subsys_initcall(misc_init);