connector.c

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/*
 *  connector.c
 *
 * 2004+ Copyright (c) Evgeniy Polyakov <[email protected]>
 * All rights reserved.
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
#include <linux/moduleparam.h>
#include <linux/connector.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/spinlock.h>

#include <net/sock.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Evgeniy Polyakov <[email protected]>");
MODULE_DESCRIPTION("Generic userspace <-> kernelspace connector.");
MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_CONNECTOR);

static struct cn_dev cdev;

static int cn_already_initialized;

/*
 * msg->seq and msg->ack are used to determine message genealogy.
 * When someone sends message it puts there locally unique sequence
 * and random acknowledge numbers.  Sequence number may be copied into
 * nlmsghdr->nlmsg_seq too.
 *
 * Sequence number is incremented with each message to be sent.
 *
 * If we expect reply to our message then the sequence number in
 * received message MUST be the same as in original message, and
 * acknowledge number MUST be the same + 1.
 *
 * If we receive a message and its sequence number is not equal to the
 * one we are expecting then it is a new message.
 *
 * If we receive a message and its sequence number is the same as one
 * we are expecting but it's acknowledgement number is not equal to
 * the acknowledgement number in the original message + 1, then it is
 * a new message.
 *
 */
int cn_netlink_send(struct cn_msg *msg, u32 __group, gfp_t gfp_mask)
{
    struct cn_callback_entry *__cbq;
    unsigned int size;
    struct sk_buff *skb;
    struct nlmsghdr *nlh;
    struct cn_msg *data;
    struct cn_dev *dev = &cdev;
    u32 group = 0;
    int found = 0;

    if (!__group) {
        spin_lock_bh(&dev->cbdev->queue_lock);
        list_for_each_entry(__cbq, &dev->cbdev->queue_list,
                    callback_entry) {
            if (cn_cb_equal(&__cbq->id.id, &msg->id)) {
                found = 1;
                group = __cbq->group;
                break;
            }
        }
        spin_unlock_bh(&dev->cbdev->queue_lock);

        if (!found)
            return -ENODEV;
    } else {
        group = __group;
    }

    if (!netlink_has_listeners(dev->nls, group))
        return -ESRCH;

    size = NLMSG_SPACE(sizeof(*msg) + msg->len);

    skb = alloc_skb(size, gfp_mask);
    if (!skb)
        return -ENOMEM;

    nlh = nlmsg_put(skb, 0, msg->seq, NLMSG_DONE, size - sizeof(*nlh), 0);
    if (!nlh) {
        kfree_skb(skb);
        return -EMSGSIZE;
    }

    data = nlmsg_data(nlh);

    memcpy(data, msg, sizeof(*data) + msg->len);

    NETLINK_CB(skb).dst_group = group;

    return netlink_broadcast(dev->nls, skb, 0, group, gfp_mask);
}
EXPORT_SYMBOL_GPL(cn_netlink_send);

/*
 * Callback helper - queues work and setup destructor for given data.
 */
static int cn_call_callback(struct sk_buff *skb)
{
    struct cn_callback_entry *i, *cbq = NULL;
    struct cn_dev *dev = &cdev;
    struct cn_msg *msg = NLMSG_DATA(nlmsg_hdr(skb));
    struct netlink_skb_parms *nsp = &NETLINK_CB(skb);
    int err = -ENODEV;

    spin_lock_bh(&dev->cbdev->queue_lock);
    list_for_each_entry(i, &dev->cbdev->queue_list, callback_entry) {
        if (cn_cb_equal(&i->id.id, &msg->id)) {
            atomic_inc(&i->refcnt);
            cbq = i;
            break;
        }
    }
    spin_unlock_bh(&dev->cbdev->queue_lock);

    if (cbq != NULL) {
        err = 0;
        cbq->callback(msg, nsp);
        kfree_skb(skb);
        cn_queue_release_callback(cbq);
        err = 0;
    }

    return err;
}

/*
 * Main netlink receiving function.
 *
 * It checks skb, netlink header and msg sizes, and calls callback helper.
 */
static void cn_rx_skb(struct sk_buff *__skb)
{
    struct nlmsghdr *nlh;
    int err;
    struct sk_buff *skb;

    skb = skb_get(__skb);

    if (skb->len >= NLMSG_SPACE(0)) {
        nlh = nlmsg_hdr(skb);

        if (nlh->nlmsg_len < sizeof(struct cn_msg) ||
            skb->len < nlh->nlmsg_len ||
            nlh->nlmsg_len > CONNECTOR_MAX_MSG_SIZE) {
            kfree_skb(skb);
            return;
        }

        err = cn_call_callback(skb);
        if (err < 0)
            kfree_skb(skb);
    }
}

/*
 * Callback add routing - adds callback with given ID and name.
 * If there is registered callback with the same ID it will not be added.
 *
 * May sleep.
 */
int cn_add_callback(struct cb_id *id, const char *name,
            void (*callback)(struct cn_msg *,
                     struct netlink_skb_parms *))
{
    int err;
    struct cn_dev *dev = &cdev;

    if (!cn_already_initialized)
        return -EAGAIN;

    err = cn_queue_add_callback(dev->cbdev, name, id, callback);
    if (err)
        return err;

    return 0;
}
EXPORT_SYMBOL_GPL(cn_add_callback);

/*
 * Callback remove routing - removes callback
 * with given ID.
 * If there is no registered callback with given
 * ID nothing happens.
 *
 * May sleep while waiting for reference counter to become zero.
 */
void cn_del_callback(struct cb_id *id)
{
    struct cn_dev *dev = &cdev;

    cn_queue_del_callback(dev->cbdev, id);
}
EXPORT_SYMBOL_GPL(cn_del_callback);

static int cn_proc_show(struct seq_file *m, void *v)
{
    struct cn_queue_dev *dev = cdev.cbdev;
    struct cn_callback_entry *cbq;

    seq_printf(m, "Name            ID\n");

    spin_lock_bh(&dev->queue_lock);

    list_for_each_entry(cbq, &dev->queue_list, callback_entry) {
        seq_printf(m, "%-15s %u:%u\n",
               cbq->id.name,
               cbq->id.id.idx,
               cbq->id.id.val);
    }

    spin_unlock_bh(&dev->queue_lock);

    return 0;
}

static int cn_proc_open(struct inode *inode, struct file *file)
{
    return single_open(file, cn_proc_show, NULL);
}

static const struct file_operations cn_file_ops = {
    .owner   = THIS_MODULE,
    .open    = cn_proc_open,
    .read    = seq_read,
    .llseek  = seq_lseek,
    .release = single_release
};

static struct cn_dev cdev = {
    .input   = cn_rx_skb,
};

static int __devinit cn_init(void)
{
    struct cn_dev *dev = &cdev;
    struct netlink_kernel_cfg cfg = {
        .groups = CN_NETLINK_USERS + 0xf,
        .input  = dev->input,
    };

    dev->nls = netlink_kernel_create(&init_net, NETLINK_CONNECTOR, &cfg);
    if (!dev->nls)
        return -EIO;

    dev->cbdev = cn_queue_alloc_dev("cqueue", dev->nls);
    if (!dev->cbdev) {
        netlink_kernel_release(dev->nls);
        return -EINVAL;
    }

    cn_already_initialized = 1;

    proc_net_fops_create(&init_net, "connector", S_IRUGO, &cn_file_ops);

    return 0;
}

static void __devexit cn_fini(void)
{
    struct cn_dev *dev = &cdev;

    cn_already_initialized = 0;

    proc_net_remove(&init_net, "connector");

    cn_queue_free_dev(dev->cbdev);
    netlink_kernel_release(dev->nls);
}

subsys_initcall(cn_init);
module_exit(cn_fini);