sir_dongle.c

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/*********************************************************************
 *
 *  sir_dongle.c:   manager for serial dongle protocol drivers
 *
 *  Copyright (c) 2002 Martin Diehl
 *
 *  This program is free software; you can redistribute it and/or 
 *  modify it under the terms of the GNU General Public License as 
 *  published by the Free Software Foundation; either version 2 of 
 *  the License, or (at your option) any later version.
 *
 ********************************************************************/    

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/kmod.h>
#include <linux/mutex.h>

#include <net/irda/irda.h>

#include "sir-dev.h"

/**************************************************************************
 *
 * dongle registration and attachment
 *
 */

static LIST_HEAD(dongle_list);          /* list of registered dongle drivers */
static DEFINE_MUTEX(dongle_list_lock);      /* protects the list */

int irda_register_dongle(struct dongle_driver *new)
{
    struct list_head *entry;
    struct dongle_driver *drv;

    IRDA_DEBUG(0, "%s : registering dongle \"%s\" (%d).\n",
           __func__, new->driver_name, new->type);

    mutex_lock(&dongle_list_lock);
    list_for_each(entry, &dongle_list) {
        drv = list_entry(entry, struct dongle_driver, dongle_list);
        if (new->type == drv->type) {
            mutex_unlock(&dongle_list_lock);
            return -EEXIST;
        }
    }
    list_add(&new->dongle_list, &dongle_list);
    mutex_unlock(&dongle_list_lock);
    return 0;
}
EXPORT_SYMBOL(irda_register_dongle);

int irda_unregister_dongle(struct dongle_driver *drv)
{
    mutex_lock(&dongle_list_lock);
    list_del(&drv->dongle_list);
    mutex_unlock(&dongle_list_lock);
    return 0;
}
EXPORT_SYMBOL(irda_unregister_dongle);

int sirdev_get_dongle(struct sir_dev *dev, IRDA_DONGLE type)
{
    struct list_head *entry;
    const struct dongle_driver *drv = NULL;
    int err = -EINVAL;

    request_module("irda-dongle-%d", type);

    if (dev->dongle_drv != NULL)
        return -EBUSY;
    
    /* serialize access to the list of registered dongles */
    mutex_lock(&dongle_list_lock);

    list_for_each(entry, &dongle_list) {
        drv = list_entry(entry, struct dongle_driver, dongle_list);
        if (drv->type == type)
            break;
        else
            drv = NULL;
    }

    if (!drv) {
        err = -ENODEV;
        goto out_unlock;    /* no such dongle */
    }

    /* handling of SMP races with dongle module removal - three cases:
     * 1) dongle driver was already unregistered - then we haven't found the
     *  requested dongle above and are already out here
     * 2) the module is already marked deleted but the driver is still
     *  registered - then the try_module_get() below will fail
     * 3) the try_module_get() below succeeds before the module is marked
     *  deleted - then sys_delete_module() fails and prevents the removal
     *  because the module is in use.
     */

    if (!try_module_get(drv->owner)) {
        err = -ESTALE;
        goto out_unlock;    /* rmmod already pending */
    }
    dev->dongle_drv = drv;

    if (!drv->open  ||  (err=drv->open(dev))!=0)
        goto out_reject;        /* failed to open driver */

    mutex_unlock(&dongle_list_lock);
    return 0;

out_reject:
    dev->dongle_drv = NULL;
    module_put(drv->owner);
out_unlock:
    mutex_unlock(&dongle_list_lock);
    return err;
}

int sirdev_put_dongle(struct sir_dev *dev)
{
    const struct dongle_driver *drv = dev->dongle_drv;

    if (drv) {
        if (drv->close)
            drv->close(dev);        /* close this dongle instance */

        dev->dongle_drv = NULL;         /* unlink the dongle driver */
        module_put(drv->owner);/* decrement driver's module refcount */
    }

    return 0;
}