// SPDX-License-Identifier: GPL-2.0
/*
 * drivers/usb/core/file.c
 *
 * (C) Copyright Linus Torvalds 1999
 * (C) Copyright Johannes Erdfelt 1999-2001
 * (C) Copyright Andreas Gal 1999
 * (C) Copyright Gregory P. Smith 1999
 * (C) Copyright Deti Fliegl 1999 (new USB architecture)
 * (C) Copyright Randy Dunlap 2000
 * (C) Copyright David Brownell 2000-2001 (kernel hotplug, usb_device_id,
 *      more docs, etc)
 * (C) Copyright Yggdrasil Computing, Inc. 2000
 *     (usb_device_id matching changes by Adam J. Richter)
 * (C) Copyright Greg Kroah-Hartman 2002-2003
 *
 * Released under the GPLv2 only.
 */

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/rwsem.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/usb.h>

#include "usb.h"

#define MAX_USB_MINORS  256
static const struct file_operations *usb_minors[MAX_USB_MINORS];
static DECLARE_RWSEM(minor_rwsem);
static DEFINE_MUTEX(init_usb_class_mutex);

static int usb_open(struct inode *inode, struct file *file)
{
        int err = -ENODEV;
        const struct file_operations *new_fops;

        down_read(&minor_rwsem);
        new_fops = fops_get(usb_minors[iminor(inode)]);

        if (!new_fops)
                goto done;

        replace_fops(file, new_fops);
        /* Curiouser and curiouser... NULL ->open() as "no device" ? */
        if (file->f_op->open)
                err = file->f_op->open(inode, file);
 done:
        up_read(&minor_rwsem);
        return err;
}

static const struct file_operations usb_fops = {
        .owner =        THIS_MODULE,
        .open =         usb_open,
        .llseek =       noop_llseek,
};

static struct usb_class {
        struct kref kref;
        struct class *class;
} *usb_class;

static char *usb_devnode(struct device *dev, umode_t *mode)
{
        struct usb_class_driver *drv;

        drv = dev_get_drvdata(dev);
        if (!drv || !drv->devnode)
                return NULL;
        return drv->devnode(dev, mode);
}

static int init_usb_class(void)
{
        int result = 0;

        if (usb_class != NULL) {
                kref_get(&usb_class->kref);
                goto exit;
        }

        usb_class = kmalloc(sizeof(*usb_class), GFP_KERNEL);
        if (!usb_class) {
                result = -ENOMEM;
                goto exit;
        }

        kref_init(&usb_class->kref);
        usb_class->class = class_create(THIS_MODULE, "usbmisc");
        if (IS_ERR(usb_class->class)) {
                result = PTR_ERR(usb_class->class);
                printk(KERN_ERR "class_create failed for usb devices\n");
                kfree(usb_class);
                usb_class = NULL;
                goto exit;
        }
        usb_class->class->devnode = usb_devnode;

exit:
        return result;
}

static void release_usb_class(struct kref *kref)
{
        /* Ok, we cheat as we know we only have one usb_class */
        class_destroy(usb_class->class);
        kfree(usb_class);
        usb_class = NULL;
}

static void destroy_usb_class(void)
{
        mutex_lock(&init_usb_class_mutex);
        kref_put(&usb_class->kref, release_usb_class);
        mutex_unlock(&init_usb_class_mutex);
}

int usb_major_init(void)
{
        int error;

        error = register_chrdev(USB_MAJOR, "usb", &usb_fops);
        if (error)
                printk(KERN_ERR "Unable to get major %d for usb devices\n",
                       USB_MAJOR);

        return error;
}

void usb_major_cleanup(void)
{
        unregister_chrdev(USB_MAJOR, "usb");
}

/**
 * usb_register_dev - register a USB device, and ask for a minor number
 * @intf: pointer to the usb_interface that is being registered
 * @class_driver: pointer to the usb_class_driver for this device
 *
 * This should be called by all USB drivers that use the USB major number.
 * If CONFIG_USB_DYNAMIC_MINORS is enabled, the minor number will be
 * dynamically allocated out of the list of available ones.  If it is not
 * enabled, the minor number will be based on the next available free minor,
 * starting at the class_driver->minor_base.
 *
 * This function also creates a usb class device in the sysfs tree.
 *
 * usb_deregister_dev() must be called when the driver is done with
 * the minor numbers given out by this function.
 *
 * Return: -EINVAL if something bad happens with trying to register a
 * device, and 0 on success.
 */
int usb_register_dev(struct usb_interface *intf,
                     struct usb_class_driver *class_driver)
{
        int retval;
        int minor_base = class_driver->minor_base;
        int minor;
        char name[20];

#ifdef CONFIG_USB_DYNAMIC_MINORS
        /*
         * We don't care what the device tries to start at, we want to start
         * at zero to pack the devices into the smallest available space with
         * no holes in the minor range.
         */
        minor_base = 0;
#endif

        if (class_driver->fops == NULL)
                return -EINVAL;
        if (intf->minor >= 0)
                return -EADDRINUSE;

        mutex_lock(&init_usb_class_mutex);
        retval = init_usb_class();
        mutex_unlock(&init_usb_class_mutex);

        if (retval)
                return retval;

        dev_dbg(&intf->dev, "looking for a minor, starting at %d\n", minor_base);

        down_write(&minor_rwsem);
        for (minor = minor_base; minor < MAX_USB_MINORS; ++minor) {
                if (usb_minors[minor])
                        continue;

                usb_minors[minor] = class_driver->fops;
                intf->minor = minor;
                break;
        }
        if (intf->minor < 0) {
                up_write(&minor_rwsem);
                return -EXFULL;
        }

        /* create a usb class device for this usb interface */
        snprintf(name, sizeof(name), class_driver->name, minor - minor_base);
        intf->usb_dev = device_create(usb_class->class, &intf->dev,
                                      MKDEV(USB_MAJOR, minor), class_driver,
                                      "%s", kbasename(name));
        if (IS_ERR(intf->usb_dev)) {
                usb_minors[minor] = NULL;
                intf->minor = -1;
                retval = PTR_ERR(intf->usb_dev);
        }
        up_write(&minor_rwsem);
        return retval;
}
EXPORT_SYMBOL_GPL(usb_register_dev);

/**
 * usb_deregister_dev - deregister a USB device's dynamic minor.
 * @intf: pointer to the usb_interface that is being deregistered
 * @class_driver: pointer to the usb_class_driver for this device
 *
 * Used in conjunction with usb_register_dev().  This function is called
 * when the USB driver is finished with the minor numbers gotten from a
 * call to usb_register_dev() (usually when the device is disconnected
 * from the system.)
 *
 * This function also removes the usb class device from the sysfs tree.
 *
 * This should be called by all drivers that use the USB major number.
 */
void usb_deregister_dev(struct usb_interface *intf,
                        struct usb_class_driver *class_driver)
{
        if (intf->minor == -1)
                return;

        dev_dbg(&intf->dev, "removing %d minor\n", intf->minor);
        device_destroy(usb_class->class, MKDEV(USB_MAJOR, intf->minor));

        down_write(&minor_rwsem);
        usb_minors[intf->minor] = NULL;
        up_write(&minor_rwsem);

        intf->usb_dev = NULL;
        intf->minor = -1;
        destroy_usb_class();
}
EXPORT_SYMBOL_GPL(usb_deregister_dev);