/*
 * NETLINK      An implementation of a loadable kernel mode driver providing
 *              multiple kernel/user space bidirectional communications links.
 *
 *              Author:         Alan Cox <alan@cymru.net>
 *
 *              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/errno.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/sched.h>
#include <linux/malloc.h>
#include <linux/ioport.h>
#include <linux/fcntl.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/skbuff.h>
#include <linux/init.h>

#include <net/netlink.h>

#include <asm/poll.h>
#include <asm/io.h>
#include <asm/uaccess.h>
#include <asm/system.h>

static int (*netlink_handler[MAX_LINKS])(int minor, struct sk_buff *skb);
static struct sk_buff_head skb_queue_rd[MAX_LINKS]; 
static int rdq_size[MAX_LINKS];
static struct wait_queue *read_space_wait[MAX_LINKS];

static unsigned long active_map = 0;
static unsigned long open_map = 0;

/*
 *      Device operations
 */
 
/*
 *      Default write handler.
 */
 
static int netlink_err(int minor, struct sk_buff *skb)
{
        kfree_skb(skb, FREE_READ);
        return -EUNATCH;
}

/*
 *      Exported do nothing receiver for one way
 *      interfaces.
 */
  
int netlink_donothing(int minor, struct sk_buff *skb)
{
        kfree_skb(skb, FREE_READ);
        return -EINVAL;
}

static unsigned int netlink_poll(struct file *file, poll_table * wait)
{
        unsigned int mask;
        unsigned int minor = MINOR(file->f_dentry->d_inode->i_rdev);

        poll_wait(&read_space_wait[minor], wait);
        mask = POLLOUT | POLLWRNORM;
        if (skb_peek(&skb_queue_rd[minor]))
                mask |= POLLIN | POLLRDNORM;
        return mask;
}

/*
 *      Write a message to the kernel side of a communication link
 */
 
static long netlink_write(struct inode * inode, struct file * file,
                          const char * buf, unsigned long count)
{
        int err; 
        unsigned int minor = MINOR(inode->i_rdev);
        struct sk_buff *skb;
        skb=alloc_skb(count, GFP_KERNEL);
        err = copy_from_user(skb_put(skb,count),buf, count);
        return err ? -EFAULT : (netlink_handler[minor])(minor,skb);
}

/*
 *      Read a message from the kernel side of the communication link
 */

static long netlink_read(struct inode * inode, struct file * file, char * buf,
                         unsigned long count)
{
        int err; 
        unsigned int minor = MINOR(inode->i_rdev);
        struct sk_buff *skb;
        cli();
        while((skb=skb_dequeue(&skb_queue_rd[minor]))==NULL)
        {
                if(file->f_flags&O_NONBLOCK)
                {
                        sti();
                        return -EAGAIN;
                }
                interruptible_sleep_on(&read_space_wait[minor]);
                if(current->signal & ~current->blocked)
                {
                        sti();
                        return -ERESTARTSYS;
                }
        }
        rdq_size[minor]-=skb->len;
        sti();
        if(skb->len<count)
                count=skb->len;
        err = copy_to_user(buf,skb->data,count);
        kfree_skb(skb, FREE_READ);
        return err ? -EFAULT : count;
}

static long long netlink_lseek(struct file * file, long long offset, int origin)
{
        return -ESPIPE;
}

static int netlink_open(struct inode * inode, struct file * file)
{
        unsigned int minor = MINOR(inode->i_rdev);
        
        if(minor>=MAX_LINKS)
                return -ENODEV;
        if(active_map&(1<<minor))
        {
                if (file->f_mode & FMODE_READ)
                {
                        if (open_map&(1<<minor))
                                return -EBUSY;
                        open_map|=(1<<minor);
                }
                MOD_INC_USE_COUNT;
                return 0;
        }
        return -EUNATCH;
}

static int netlink_release(struct inode * inode, struct file * file)
{
        unsigned int minor = MINOR(inode->i_rdev);
        if (file->f_mode & FMODE_READ)
                open_map&=~(1<<minor);
        MOD_DEC_USE_COUNT;
        return 0;
}


static int netlink_ioctl(struct inode *inode, struct file *file,
                    unsigned int cmd, unsigned long arg)
{
        unsigned int minor = MINOR(inode->i_rdev);
        int retval = 0;

        if (minor >= MAX_LINKS)
                return -ENODEV;
        switch ( cmd ) {
                default:
                        retval = -EINVAL;
        }
        return retval;
}


static struct file_operations netlink_fops = {
        netlink_lseek,
        netlink_read,
        netlink_write,
        NULL,           /* netlink_readdir */
        netlink_poll,
        netlink_ioctl,
        NULL,           /* netlink_mmap */
        netlink_open,
        netlink_release
};

/*
 *      We export these functions to other modules. They provide a 
 *      complete set of kernel non-blocking support for message
 *      queueing.
 */
 
int netlink_attach(int unit, int (*function)(int minor, struct sk_buff *skb))
{
        if(unit>=MAX_LINKS)
                return -ENODEV;
        if(active_map&(1<<unit))
                return -EBUSY;
        active_map|=(1<<unit);
        netlink_handler[unit]=function;
        return 0;
}

void netlink_detach(int unit)
{
        active_map&=~(1<<unit);
        netlink_handler[unit]=netlink_err;
}

int netlink_post(int unit, struct sk_buff *skb)
{
        unsigned long flags;
        int ret=-EUNATCH;
        if(open_map&(1<<unit))
        {
                save_flags(flags);
                cli();
                if(rdq_size[unit]+skb->len>MAX_QBYTES)
                        ret=-EAGAIN;
                else
                {       
                        skb_queue_tail(&skb_queue_rd[unit], skb);
                        rdq_size[unit]+=skb->len;
                        ret=0;
                        wake_up_interruptible(&read_space_wait[unit]);
                }
                restore_flags(flags);
        }
        return ret;
}


/*
 *      "High" level netlink interface. (ANK)
 *      
 *      Features:
 *              - standard message format.
 *              - pseudo-reliable delivery. Messages can be still lost, but
 *                user level will know that they were lost and can
 *                recover (f.e. gated could reread FIB and device list)
 *              - messages are batched.
 *              - if user is not attached, we do not make useless work.
 *
 *      Examples:
 *              - netlink_post equivalent (but with pseudo-reliable delivery)
 *                      ctl.nlmsg_delay = 0;
 *                      ctl.nlmsg_maxsize = <one message size>;
 *                      ....
 *                      msg = nlmsg_send(&ctl, ...);
 *                      if (msg) {
 *                              ... make it ...
 *                              nlmsg_transmit(&ctl);
 *                      }
 *
 *              - batched messages.
 *                      if nlmsg_delay==0, messages are delivered only
 *                      by nlmsg_transmit, or when batch is completed,
 *                      otherwise nlmsg_transmit is noop (only starts
 *                      timer)
 *
 *                      ctl.nlmsg_delay = ...;
 *                      ctl.nlmsg_maxsize = <one batch size>;
 *                      ....
 *                      msg = nlmsg_send(&ctl, ...);
 *                      if (msg)
 *                              ... make it ...
 *                      ....
 *                      msg = nlmsg_send(&ctl, ...);
 *                      if (msg)
 *                              ... make it ...
 *                      ....
 *                      if (ctl.nlmsg_skb)
 *                              nlmsg_transmit(&ctl);
 *
 */

/*
 *      Try to deliver queued messages.
 *      If the delivery fails (netlink is not attached or congested),
 *      do not free skb to avoid useless new message creation.
 *
 *      Notes:
 *              - timer should be already stopped.
 *              - NET SPL.
 */

void nlmsg_flush(struct nlmsg_ctl *ctl)
{
        if (ctl->nlmsg_skb == NULL)
                return;

        if (netlink_post(ctl->nlmsg_unit, ctl->nlmsg_skb) == 0)
        {
                ctl->nlmsg_skb = NULL;
                return;
        }

        ctl->nlmsg_timer.expires = jiffies + NLMSG_RECOVERY_TIMEO;
        ctl->nlmsg_timer.data = (unsigned long)ctl;
        ctl->nlmsg_timer.function = (void (*)(unsigned long))nlmsg_flush;
        add_timer(&ctl->nlmsg_timer);
        return;
}


/*
 *      Allocate room for new message. If it is impossible,
 *      start "overrun" mode and return NULL.
 *
 *      Notes:
 *              - NET SPL.
 */

void* nlmsg_send(struct nlmsg_ctl *ctl, unsigned long type, int len,
                 unsigned long seq, unsigned long pid)
{
        struct nlmsghdr *nlh;
        struct sk_buff *skb;
        int     rlen;

        static __inline__ void nlmsg_lost(struct nlmsg_ctl *ctl,
                                          unsigned long seq)
        {
                if (!ctl->nlmsg_overrun)
                {
                        ctl->nlmsg_overrun_start = seq;
                        ctl->nlmsg_overrun_end = seq;
                        ctl->nlmsg_overrun = 1;
                        return;
                }
                if (!ctl->nlmsg_overrun_start)
                        ctl->nlmsg_overrun_start = seq;
                if (seq)
                        ctl->nlmsg_overrun_end = seq;
        }

        if (!(open_map&(1<<ctl->nlmsg_unit)))
        {
                nlmsg_lost(ctl, seq);
                return NULL;
        }

        rlen = NLMSG_ALIGN(len + sizeof(struct nlmsghdr));

        if (rlen > ctl->nlmsg_maxsize)
        {
                printk(KERN_ERR "nlmsg_send: too big message\n");
                return NULL;
        }

        if ((skb=ctl->nlmsg_skb) == NULL || skb_tailroom(skb) < rlen)
        {
                if (skb)
                {
                        ctl->nlmsg_force++;
                        nlmsg_flush(ctl);
                        ctl->nlmsg_force--;
                }

                if (ctl->nlmsg_skb ||
                    (skb=alloc_skb(ctl->nlmsg_maxsize, GFP_ATOMIC)) == NULL)
                {
                        printk (KERN_WARNING "nlmsg at unit %d overrunned\n", ctl->nlmsg_unit);
                        nlmsg_lost(ctl, seq);
                        return NULL;
                }

                ctl->nlmsg_skb = skb;

                if (ctl->nlmsg_overrun)
                {
                        int *seqp;
                        nlh = (struct nlmsghdr*)skb_put(skb, sizeof(struct nlmsghdr) + 2*sizeof(unsigned long));
                        nlh->nlmsg_type = NLMSG_OVERRUN;
                        nlh->nlmsg_len = sizeof(struct nlmsghdr) + 2*sizeof(unsigned long);
                        nlh->nlmsg_seq = 0;
                        nlh->nlmsg_pid = 0;
                        seqp = (int*)nlh->nlmsg_data;
                        seqp[0] = ctl->nlmsg_overrun_start;
                        seqp[1] = ctl->nlmsg_overrun_end;
                        ctl->nlmsg_overrun = 0;
                }
                if (ctl->nlmsg_timer.function)
                {
                        del_timer(&ctl->nlmsg_timer);
                        ctl->nlmsg_timer.function = NULL;
                }
                if (ctl->nlmsg_delay)
                {
                        ctl->nlmsg_timer.expires = jiffies + ctl->nlmsg_delay;
                        ctl->nlmsg_timer.function = (void (*)(unsigned long))nlmsg_flush;
                        ctl->nlmsg_timer.data = (unsigned long)ctl;
                        add_timer(&ctl->nlmsg_timer);
                }
        }

        nlh = (struct nlmsghdr*)skb_put(skb, rlen);
        nlh->nlmsg_type = type;
        nlh->nlmsg_len = sizeof(struct nlmsghdr) + len;
        nlh->nlmsg_seq = seq;
        nlh->nlmsg_pid = pid;
        return nlh->nlmsg_data;
}

/*
 *      Kick message queue.
 *      Two modes:
 *              - synchronous (delay==0). Messages are delivered immediately.
 *              - delayed. Do not deliver, but start delivery timer.
 */

void nlmsg_transmit(struct nlmsg_ctl *ctl)
{
        start_bh_atomic();

        if (!ctl->nlmsg_delay)
        {
                if (ctl->nlmsg_timer.function)
                {
                        del_timer(&ctl->nlmsg_timer);
                        ctl->nlmsg_timer.function = NULL;
                }
                ctl->nlmsg_force++;
                nlmsg_flush(ctl);
                ctl->nlmsg_force--;
                end_bh_atomic();
                return;
        }
        if (!ctl->nlmsg_timer.function)
        {
                ctl->nlmsg_timer.expires = jiffies + ctl->nlmsg_delay;
                ctl->nlmsg_timer.function = (void (*)(unsigned long))nlmsg_flush;
                ctl->nlmsg_timer.data = (unsigned long)ctl;
                add_timer(&ctl->nlmsg_timer);
        }

        end_bh_atomic();
}


__initfunc(int init_netlink(void))
{
        int ct;

        if(register_chrdev(NETLINK_MAJOR,"netlink", &netlink_fops)) {
                printk(KERN_ERR "netlink: unable to get major %d\n", NETLINK_MAJOR);
                return -EIO;
        }
        for(ct=0;ct<MAX_LINKS;ct++)
        {
                skb_queue_head_init(&skb_queue_rd[ct]);
                netlink_handler[ct]=netlink_err;
        }
        return 0;
}

#ifdef MODULE

int init_module(void)
{
        printk(KERN_INFO "Network Kernel/User communications module 0.05\n");
        return init_netlink();
}

void cleanup_module(void)
{
        unregister_chrdev(NET_MAJOR,"netlink");
}

#endif