/*
 * libusual
 *
 * The libusual contains the table of devices common for ub and usb-storage.
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/usb.h>
#include <linux/usb_usual.h>
#include <linux/vmalloc.h>
#include <linux/kthread.h>
#include <linux/mutex.h>

/*
 */
#define USU_MOD_FL_THREAD   1   /* Thread is running */
#define USU_MOD_FL_PRESENT  2   /* The module is loaded */

struct mod_status {
        unsigned long fls;
};

static struct mod_status stat[3];
static DEFINE_SPINLOCK(usu_lock);

/*
 */
#define USB_US_DEFAULT_BIAS     USB_US_TYPE_STOR
static atomic_t usu_bias = ATOMIC_INIT(USB_US_DEFAULT_BIAS);

#define BIAS_NAME_SIZE  (sizeof("usb-storage"))
static const char *bias_names[3] = { "none", "usb-storage", "ub" };

static DEFINE_MUTEX(usu_probe_mutex);
static DECLARE_COMPLETION(usu_end_notify);
static atomic_t total_threads = ATOMIC_INIT(0);

static int usu_probe_thread(void *arg);

/*
 * @type: the module type as an integer
 */
void usb_usual_set_present(int type)
{
        struct mod_status *st;
        unsigned long flags;

        if (type <= 0 || type >= 3)
                return;
        st = &stat[type];
        spin_lock_irqsave(&usu_lock, flags);
        st->fls |= USU_MOD_FL_PRESENT;
        spin_unlock_irqrestore(&usu_lock, flags);
}
EXPORT_SYMBOL_GPL(usb_usual_set_present);

void usb_usual_clear_present(int type)
{
        struct mod_status *st;
        unsigned long flags;

        if (type <= 0 || type >= 3)
                return;
        st = &stat[type];
        spin_lock_irqsave(&usu_lock, flags);
        st->fls &= ~USU_MOD_FL_PRESENT;
        spin_unlock_irqrestore(&usu_lock, flags);
}
EXPORT_SYMBOL_GPL(usb_usual_clear_present);

/*
 * Match the calling driver type against the table.
 * Returns: 0 if the device matches.
 */
int usb_usual_check_type(const struct usb_device_id *id, int caller_type)
{
        int id_type = USB_US_TYPE(id->driver_info);

        if (caller_type <= 0 || caller_type >= 3)
                return -EINVAL;

        /* Drivers grab fixed assignment devices */
        if (id_type == caller_type)
                return 0;
        /* Drivers grab devices biased to them */
        if (id_type == USB_US_TYPE_NONE && caller_type == atomic_read(&usu_bias))
                return 0;
        return -ENODEV;
}
EXPORT_SYMBOL_GPL(usb_usual_check_type);

/*
 */
static int usu_probe(struct usb_interface *intf,
                         const struct usb_device_id *id)
{
        int rc;
        unsigned long type;
        struct task_struct* task;
        unsigned long flags;

        type = USB_US_TYPE(id->driver_info);
        if (type == 0)
                type = atomic_read(&usu_bias);

        spin_lock_irqsave(&usu_lock, flags);
        if ((stat[type].fls & (USU_MOD_FL_THREAD|USU_MOD_FL_PRESENT)) != 0) {
                spin_unlock_irqrestore(&usu_lock, flags);
                return -ENXIO;
        }
        stat[type].fls |= USU_MOD_FL_THREAD;
        spin_unlock_irqrestore(&usu_lock, flags);

        task = kthread_run(usu_probe_thread, (void*)type, "libusual_%ld", type);
        if (IS_ERR(task)) {
                rc = PTR_ERR(task);
                printk(KERN_WARNING "libusual: "
                    "Unable to start the thread for %s: %d\n",
                    bias_names[type], rc);
                spin_lock_irqsave(&usu_lock, flags);
                stat[type].fls &= ~USU_MOD_FL_THREAD;
                spin_unlock_irqrestore(&usu_lock, flags);
                return rc;      /* Not being -ENXIO causes a message printed */
        }
        atomic_inc(&total_threads);

        return -ENXIO;
}

static void usu_disconnect(struct usb_interface *intf)
{
        ;       /* We should not be here. */
}

static struct usb_driver usu_driver = {
        .name =         "libusual",
        .probe =        usu_probe,
        .disconnect =   usu_disconnect,
        .id_table =     usb_storage_usb_ids,
};

/*
 * A whole new thread for a purpose of request_module seems quite stupid.
 * The request_module forks once inside again. However, if we attempt
 * to load a storage module from our own modprobe thread, that module
 * references our symbols, which cannot be resolved until our module is
 * initialized. I wish there was a way to wait for the end of initialization.
 * The module notifier reports MODULE_STATE_COMING only.
 * So, we wait until module->init ends as the next best thing.
 */
static int usu_probe_thread(void *arg)
{
        int type = (unsigned long) arg;
        struct mod_status *st = &stat[type];
        int rc;
        unsigned long flags;

        mutex_lock(&usu_probe_mutex);
        rc = request_module(bias_names[type]);
        spin_lock_irqsave(&usu_lock, flags);
        if (rc == 0 && (st->fls & USU_MOD_FL_PRESENT) == 0) {
                /*
                 * This should not happen, but let us keep tabs on it.
                 */
                printk(KERN_NOTICE "libusual: "
                    "modprobe for %s succeeded, but module is not present\n",
                    bias_names[type]);
        }
        st->fls &= ~USU_MOD_FL_THREAD;
        spin_unlock_irqrestore(&usu_lock, flags);
        mutex_unlock(&usu_probe_mutex);

        complete_and_exit(&usu_end_notify, 0);
}

/*
 */
static int __init usb_usual_init(void)
{
        int rc;

        mutex_lock(&usu_probe_mutex);
        rc = usb_register(&usu_driver);
        mutex_unlock(&usu_probe_mutex);
        return rc;
}

static void __exit usb_usual_exit(void)
{
        /*
         * We do not check for any drivers present, because
         * they keep us pinned with symbol references.
         */

        usb_deregister(&usu_driver);

        while (atomic_read(&total_threads) > 0) {
                wait_for_completion(&usu_end_notify);
                atomic_dec(&total_threads);
        }
}

/*
 * Validate and accept the bias parameter.
 */
static int usu_set_bias(const char *bias_s, struct kernel_param *kp)
{
        int i;
        int len;
        int bias_n = 0;

        len = strlen(bias_s);
        if (len == 0)
                return -EDOM;
        if (bias_s[len-1] == '\n')
                --len;

        for (i = 1; i < 3; i++) {
                if (strncmp(bias_s, bias_names[i], len) == 0) {
                        bias_n = i;
                        break;
                }
        }
        if (bias_n == 0)
                return -EINVAL;

        atomic_set(&usu_bias, bias_n);
        return 0;
}

static int usu_get_bias(char *buffer, struct kernel_param *kp)
{
        return strlen(strcpy(buffer, bias_names[atomic_read(&usu_bias)]));
}

module_init(usb_usual_init);
module_exit(usb_usual_exit);

module_param_call(bias, usu_set_bias, usu_get_bias, NULL, S_IRUGO|S_IWUSR);
__MODULE_PARM_TYPE(bias, "string");
MODULE_PARM_DESC(bias, "Bias to usb-storage or ub");

MODULE_LICENSE("GPL");