// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/err.h>

#include <linux/usb/composite.h>

static LIST_HEAD(func_list);
static DEFINE_MUTEX(func_lock);

static struct usb_function_instance *try_get_usb_function_instance(const char *name)
{
        struct usb_function_driver *fd;
        struct usb_function_instance *fi;

        fi = ERR_PTR(-ENOENT);
        mutex_lock(&func_lock);
        list_for_each_entry(fd, &func_list, list) {

                if (strcmp(name, fd->name))
                        continue;

                if (!try_module_get(fd->mod)) {
                        fi = ERR_PTR(-EBUSY);
                        break;
                }
                fi = fd->alloc_inst();
                if (IS_ERR(fi))
                        module_put(fd->mod);
                else
                        fi->fd = fd;
                break;
        }
        mutex_unlock(&func_lock);
        return fi;
}

struct usb_function_instance *usb_get_function_instance(const char *name)
{
        struct usb_function_instance *fi;
        int ret;

        fi = try_get_usb_function_instance(name);
        if (!IS_ERR(fi))
                return fi;
        ret = PTR_ERR(fi);
        if (ret != -ENOENT)
                return fi;
        ret = request_module("usbfunc:%s", name);
        if (ret < 0)
                return ERR_PTR(ret);
        return try_get_usb_function_instance(name);
}
EXPORT_SYMBOL_GPL(usb_get_function_instance);

struct usb_function *usb_get_function(struct usb_function_instance *fi)
{
        struct usb_function *f;

        f = fi->fd->alloc_func(fi);
        if (IS_ERR(f))
                return f;
        f->fi = fi;
        return f;
}
EXPORT_SYMBOL_GPL(usb_get_function);

void usb_put_function_instance(struct usb_function_instance *fi)
{
        struct module *mod;

        if (!fi)
                return;

        mod = fi->fd->mod;
        fi->free_func_inst(fi);
        module_put(mod);
}
EXPORT_SYMBOL_GPL(usb_put_function_instance);

void usb_put_function(struct usb_function *f)
{
        if (!f)
                return;

        f->free_func(f);
}
EXPORT_SYMBOL_GPL(usb_put_function);

int usb_function_register(struct usb_function_driver *newf)
{
        struct usb_function_driver *fd;
        int ret;

        ret = -EEXIST;

        mutex_lock(&func_lock);
        list_for_each_entry(fd, &func_list, list) {
                if (!strcmp(fd->name, newf->name))
                        goto out;
        }
        ret = 0;
        list_add_tail(&newf->list, &func_list);
out:
        mutex_unlock(&func_lock);
        return ret;
}
EXPORT_SYMBOL_GPL(usb_function_register);

void usb_function_unregister(struct usb_function_driver *fd)
{
        mutex_lock(&func_lock);
        list_del(&fd->list);
        mutex_unlock(&func_lock);
}
EXPORT_SYMBOL_GPL(usb_function_unregister);