// SPDX-License-Identifier: GPL-2.0
/*
 * 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%q106fm.uucp@wupost.wustl.edu) (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 <pjb27@cam.ac.uk>
 *
 * Fixed a failing symbol register to free the device registration
 *              Alan Cox <alan@lxorguk.ukuu.org.uk> 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 <jack@solucorp.qc.ca>,
 *  adapted by Bjorn Ekwall <bj0rn@blox.se>
 *  corrected by Alan Cox <alan@lxorguk.ukuu.org.uk>
 *
 * Changes for kmod (from kerneld):
 *      Cyrus Durgin <cider@speakeasy.org>
 *
 * Added devfs support. Richard Gooch <rgooch@atnf.csiro.au>  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 128 /* 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,
};
#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 *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;
        }

        /*
         * Place the miscdevice in the file's
         * private_data so it can be used by the
         * file operations, including f_op->open below
         */
        file->private_data = c;

        err = 0;
        replace_fops(file, new_fops);
        if (file->f_op->open)
                err = file->f_op->open(inode, file);
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,
};

/**
 *      misc_register   -       register a miscellaneous device
 *      @misc: device structure
 *
 *      Register a miscellaneous device with the kernel. If the minor
 *      number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
 *      and placed in the minor field of the structure. For other cases
 *      the minor number requested is used.
 *
 *      The structure passed is linked into the kernel and may not be
 *      destroyed until it has been unregistered. By default, an open()
 *      syscall to the device sets file->private_data to point to the
 *      structure. Drivers don't need open in fops for this.
 *
 *      A zero is returned on success and a negative errno code for
 *      failure.
 */

int misc_register(struct miscdevice *misc)
{
        dev_t dev;
        int err = 0;
        bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);

        INIT_LIST_HEAD(&misc->list);

        mutex_lock(&misc_mtx);

        if (is_dynamic) {
                int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);

                if (i >= DYNAMIC_MINORS) {
                        err = -EBUSY;
                        goto out;
                }
                misc->minor = DYNAMIC_MINORS - i - 1;
                set_bit(i, misc_minors);
        } else {
                struct miscdevice *c;

                list_for_each_entry(c, &misc_list, list) {
                        if (c->minor == misc->minor) {
                                err = -EBUSY;
                                goto out;
                        }
                }
        }

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

        misc->this_device =
                device_create_with_groups(misc_class, misc->parent, dev,
                                          misc, misc->groups, "%s", misc->name);
        if (IS_ERR(misc->this_device)) {
                if (is_dynamic) {
                        int i = DYNAMIC_MINORS - misc->minor - 1;

                        if (i < DYNAMIC_MINORS && i >= 0)
                                clear_bit(i, misc_minors);
                        misc->minor = MISC_DYNAMIC_MINOR;
                }
                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;
}
EXPORT_SYMBOL(misc_register);

/**
 *      misc_deregister - unregister a miscellaneous device
 *      @misc: device to unregister
 *
 *      Unregister a miscellaneous device that was previously
 *      successfully registered with misc_register().
 */

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

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

        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);
}
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;
        struct proc_dir_entry *ret;

        ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
        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:
        pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
        class_destroy(misc_class);
fail_remove:
        if (ret)
                remove_proc_entry("misc", NULL);
        return err;
}
subsys_initcall(misc_init);