6pack.c

linux-2.6.15.6

/*
 * 6pack.c	This module implements the 6pack protocol for kernel-based
 *		devices like TTY. It interfaces between a raw TTY and the
 *		kernel's AX.25 protocol layers.
 *
 * Authors:	Andreas K鰊sgen <[e-mail]>
 *              Ralf Baechle DL5RB <[e-mail]>
 *
 * Quite a lot of stuff "stolen" by Joerg Reuter from slip.c, written by
 *
 *		Laurence Culhane, <[e-mail]>
 *		Fred N. van Kempen, <[e-mail]>
 */

#include <linux/config.h>
#include <linux/module.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <linux/bitops.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/tty.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/timer.h>
#include <net/ax25.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/spinlock.h>
#include <linux/if_arp.h>
#include <linux/init.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <asm/semaphore.h>
#include <asm/atomic.h>

#define SIXPACK_VERSION    "Revision: 0.3.0"

/* sixpack priority commands */
#define SIXP_SEOF		0x40	/* start and end of a 6pack frame */
#define SIXP_TX_URUN		0x48	/* transmit overrun */
#define SIXP_RX_ORUN		0x50	/* receive overrun */
#define SIXP_RX_BUF_OVL		0x58	/* receive buffer overflow */

#define SIXP_CHKSUM		0xFF	/* valid checksum of a 6pack frame */

/* masks to get certain bits out of the status bytes sent by the TNC */

#define SIXP_CMD_MASK		0xC0
#define SIXP_CHN_MASK		0x07
#define SIXP_PRIO_CMD_MASK	0x80
#define SIXP_STD_CMD_MASK	0x40
#define SIXP_PRIO_DATA_MASK	0x38
#define SIXP_TX_MASK		0x20
#define SIXP_RX_MASK		0x10
#define SIXP_RX_DCD_MASK	0x18
#define SIXP_LEDS_ON		0x78
#define SIXP_LEDS_OFF		0x60
#define SIXP_CON		0x08
#define SIXP_STA		0x10

#define SIXP_FOUND_TNC		0xe9
#define SIXP_CON_ON		0x68
#define SIXP_DCD_MASK		0x08
#define SIXP_DAMA_OFF		0

/* default level 2 parameters */
#define SIXP_TXDELAY			(HZ/4)	/* in 1 s */
#define SIXP_PERSIST			50	/* in 256ths */
#define SIXP_SLOTTIME			(HZ/10)	/* in 1 s */
#define SIXP_INIT_RESYNC_TIMEOUT	(3*HZ/2) /* in 1 s */
#define SIXP_RESYNC_TIMEOUT		5*HZ	/* in 1 s */

/* 6pack configuration. */
#define SIXP_NRUNIT			31      /* MAX number of 6pack channels */
#define SIXP_MTU			256	/* Default MTU */

enum sixpack_flags {
	SIXPF_ERROR,	/* Parity, etc. error	*/
};

struct sixpack {
	/* Various fields. */
	struct tty_struct	*tty;		/* ptr to TTY structure	*/
	struct net_device	*dev;		/* easy for intr handling  */

	/* These are pointers to the malloc()ed frame buffers. */
	unsigned char		*rbuff;		/* receiver buffer	*/
	int			rcount;         /* received chars counter  */
	unsigned char		*xbuff;		/* transmitter buffer	*/
	unsigned char		*xhead;         /* next byte to XMIT */
	int			xleft;          /* bytes left in XMIT queue  */

	unsigned char		raw_buf[4];
	unsigned char		cooked_buf[400];

	unsigned int		rx_count;
	unsigned int		rx_count_cooked;

	/* 6pack interface statistics. */
	struct net_device_stats stats;

	int			mtu;		/* Our mtu (to spot changes!) */
	int			buffsize;       /* Max buffers sizes */

	unsigned long		flags;		/* Flag values/ mode etc */
	unsigned char		mode;		/* 6pack mode */

	/* 6pack stuff */
	unsigned char		tx_delay;
	unsigned char		persistence;
	unsigned char		slottime;
	unsigned char		duplex;
	unsigned char		led_state;
	unsigned char		status;
	unsigned char		status1;
	unsigned char		status2;
	unsigned char		tx_enable;
	unsigned char		tnc_state;

	struct timer_list	tx_t;
	struct timer_list	resync_t;
	atomic_t		refcnt;
	struct semaphore	dead_sem;
	spinlock_t		lock;
};

#define AX25_6PACK_HEADER_LEN 0

static void sixpack_decode(struct sixpack *, unsigned char[], int);
static int encode_sixpack(unsigned char *, unsigned char *, int, unsigned char);

/*
 * Perform the persistence/slottime algorithm for CSMA access. If the
 * persistence check was successful, write the data to the serial driver.
 * Note that in case of DAMA operation, the data is not sent here.
 */

static void sp_xmit_on_air(unsigned long channel)
{
	struct sixpack *sp = (struct sixpack *) channel;
	int actual, when = sp->slottime;
	static unsigned char random;

	random = random * 17 + 41;

	if (((sp->status1 & SIXP_DCD_MASK) == 0) && (random < sp->persistence)) {
		sp->led_state = 0x70;
		sp->tty->driver->write(sp->tty, &sp->led_state, 1);
		sp->tx_enable = 1;
		actual = sp->tty->driver->write(sp->tty, sp->xbuff, sp->status2);
		sp->xleft -= actual;
		sp->xhead += actual;
		sp->led_state = 0x60;
		sp->tty->driver->write(sp->tty, &sp->led_state, 1);
		sp->status2 = 0;
	} else
		mod_timer(&sp->tx_t, jiffies + ((when + 1) * HZ) / 100);
}

/* ----> 6pack timer interrupt handler and friends. <---- */

/* Encapsulate one AX.25 frame and stuff into a TTY queue. */
static void sp_encaps(struct sixpack *sp, unsigned char *icp, int len)
{
	unsigned char *msg, *p = icp;
	int actual, count;

	if (len > sp->mtu) {	/* sp->mtu = AX25_MTU = max. PACLEN = 256 */
		msg = "oversized transmit packet!";
		goto out_drop;
	}

	if (len > sp->mtu) {	/* sp->mtu = AX25_MTU = max. PACLEN = 256 */
		msg = "oversized transmit packet!";
		goto out_drop;
	}

	if (p[0] > 5) {
		msg = "invalid KISS command";
		goto out_drop;
	}

	if ((p[0] != 0) && (len > 2)) {
		msg = "KISS control packet too long";
		goto out_drop;
	}

	if ((p[0] == 0) && (len < 15)) {
		msg = "bad AX.25 packet to transmit";
		goto out_drop;
	}

	count = encode_sixpack(p, sp->xbuff, len, sp->tx_delay);
	set_bit(TTY_DO_WRITE_WAKEUP, &sp->tty->flags);

	switch (p[0]) {
	case 1:	sp->tx_delay = p[1];
		return;
	case 2:	sp->persistence = p[1];
		return;
	case 3:	sp->slottime = p[1];
		return;
	case 4:	/* ignored */
		return;
	case 5:	sp->duplex = p[1];
		return;
	}

	if (p[0] != 0)
		return;

	/*
	 * In case of fullduplex or DAMA operation, we don't take care about the
	 * state of the DCD or of any timers, as the determination of the
	 * correct time to send is the job of the AX.25 layer. We send
	 * immediately after data has arrived.
	 */
	if (sp->duplex == 1) {
		sp->led_state = 0x70;
		sp->tty->driver->write(sp->tty, &sp->led_state, 1);
		sp->tx_enable = 1;
		actual = sp->tty->driver->write(sp->tty, sp->xbuff, count);
		sp->xleft = count - actual;
		sp->xhead = sp->xbuff + actual;
		sp->led_state = 0x60;
		sp->tty->driver->write(sp->tty, &sp->led_state, 1);
	} else {
		sp->xleft = count;
		sp->xhead = sp->xbuff;
		sp->status2 = count;
		sp_xmit_on_air((unsigned long)sp);
	}

	return;

out_drop:
	sp->stats.tx_dropped++;
	netif_start_queue(sp->dev);
	if (net_ratelimit())
		printk(KERN_DEBUG "%s: %s - dropped.\n", sp->dev->name, msg);
}

/* Encapsulate an IP datagram and kick it into a TTY queue. */

static int sp_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct sixpack *sp = netdev_priv(dev);

	spin_lock_bh(&sp->lock);
	/* We were not busy, so we are now... :-) */
	netif_stop_queue(dev);
	sp->stats.tx_bytes += skb->len;
	sp_encaps(sp, skb->data, skb->len);
	spin_unlock_bh(&sp->lock);

	dev_kfree_skb(skb);

	return 0;
}

static int sp_open_dev(struct net_device *dev)
{
	struct sixpack *sp = netdev_priv(dev);

	if (sp->tty == NULL)
		return -ENODEV;
	return 0;
}

/* Close the low-level part of the 6pack channel. */
static int sp_close(struct net_device *dev)
{
	struct sixpack *sp = netdev_priv(dev);

	spin_lock_bh(&sp->lock);
	if (sp->tty) {
		/* TTY discipline is running. */
		clear_bit(TTY_DO_WRITE_WAKEUP, &sp->tty->flags);
	}
	netif_stop_queue(dev);
	spin_unlock_bh(&sp->lock);

	return 0;
}

/* Return the frame type ID */
static int sp_header(struct sk_buff *skb, struct net_device *dev,
	unsigned short type, void *daddr, void *saddr, unsigned len)
{
#ifdef CONFIG_INET
	if (type != htons(ETH_P_AX25))
		return ax25_hard_header(skb, dev, type, daddr, saddr, len);
#endif
	return 0;
}

static struct net_device_stats *sp_get_stats(struct net_device *dev)
{
	struct sixpack *sp = netdev_priv(dev);
	return &sp->stats;
}

static int sp_set_mac_address(struct net_device *dev, void *addr)
{
	struct sockaddr_ax25 *sa = addr;

	spin_lock_irq(&dev->xmit_lock);
	memcpy(dev->dev_addr, &sa->sax25_call, AX25_ADDR_LEN);
	spin_unlock_irq(&dev->xmit_lock);

	return 0;
}

static int sp_rebuild_header(struct sk_buff *skb)
{
#ifdef CONFIG_INET
	return ax25_rebuild_header(skb);
#else
	return 0;
#endif
}

static void sp_setup(struct net_device *dev)
{
	static char ax25_bcast[AX25_ADDR_LEN] =
		{'Q'<<1,'S'<<1,'T'<<1,' '<<1,' '<<1,' '<<1,'0'<<1};
	static char ax25_test[AX25_ADDR_LEN] =
		{'L'<<1,'I'<<1,'N'<<1,'U'<<1,'X'<<1,' '<<1,'1'<<1};

	/* Finish setting up the DEVICE info. */
	dev->mtu		= SIXP_MTU;
	dev->hard_start_xmit	= sp_xmit;
	dev->open		= sp_open_dev;
	dev->destructor		= free_netdev;
	dev->stop		= sp_close;
	dev->hard_header	= sp_header;
	dev->get_stats	        = sp_get_stats;
	dev->set_mac_address    = sp_set_mac_address;
	dev->hard_header_len	= AX25_MAX_HEADER_LEN;
	dev->addr_len		= AX25_ADDR_LEN;
	dev->type		= ARPHRD_AX25;
	dev->tx_queue_len	= 10;
	dev->rebuild_header	= sp_rebuild_header;
	dev->tx_timeout		= NULL;

	/* Only activated in AX.25 mode */
	memcpy(dev->broadcast, ax25_bcast, AX25_ADDR_LEN);
	memcpy(dev->dev_addr, ax25_test, AX25_ADDR_LEN);

	SET_MODULE_OWNER(dev);

	dev->flags		= 0;
}

/* Send one completely decapsulated IP datagram to the IP layer. */

/*
 * This is the routine that sends the received data to the kernel AX.25.
 * 'cmd' is the KISS command. For AX.25 data, it is zero.
 */

static void sp_bump(struct sixpack *sp, char cmd)
{
	struct sk_buff *skb;
	int count;
	unsigned char *ptr;

	count = sp->rcount + 1;

	sp->stats.rx_bytes += count;

	if ((skb = dev_alloc_skb(count)) == NULL)
		goto out_mem;

	ptr = skb_put(skb, count);
	*ptr++ = cmd;	/* KISS command */

	memcpy(ptr, sp->cooked_buf + 1, count);
	skb->protocol = ax25_type_trans(skb, sp->dev);
	netif_rx(skb);
	sp->dev->last_rx = jiffies;
	sp->stats.rx_packets++;

	return;

out_mem:
	sp->stats.rx_dropped++;
}


/* ----------------------------------------------------------------------- */

/*
 * We have a potential race on dereferencing tty->disc_data, because the tty
 * layer provides no locking at all - thus one cpu could be running
 * sixpack_receive_buf while another calls sixpack_close, which zeroes
 * tty->disc_data and frees the memory that sixpack_receive_buf is using.  The
 * best way to fix this is to use a rwlock in the tty struct, but for now we
 * use a single global rwlock for all ttys in ppp line discipline.
 */
static DEFINE_RWLOCK(disc_data_lock);
                                                                                
static struct sixpack *sp_get(struct tty_struct *tty)
{
	struct sixpack *sp;

	read_lock(&disc_data_lock);
	sp = tty->disc_data;
	if (sp)
		atomic_inc(&sp->refcnt);
	read_unlock(&disc_data_lock);

	return sp;
}

static void sp_put(struct sixpack *sp)
{
	if (atomic_dec_and_test(&sp->refcnt))
		up(&sp->dead_sem);
}

/*
 * Called by the TTY driver when there's room for more data.  If we have
 * more packets to send, we send them here.
 */
static void sixpack_write_wakeup(struct tty_struct *tty)
{
	struct sixpack *sp = sp_get(tty);
	int actual;

	if (!sp)
		return;
	if (sp->xleft <= 0)  {
		/* Now serial buffer is almost free & we can start
		 * transmission of another packet */
		sp->stats.tx_packets++;
		clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
		sp->tx_enable = 0;
		netif_wake_queue(sp->dev);
		goto out;
	}

	if (sp->tx_enable) {
		actual = tty->driver->write(tty, sp->xhead, sp->xleft);
		sp->xleft -= actual;
		sp->xhead += actual;
	}

out:
	sp_put(sp);
}

/* ----------------------------------------------------------------------- */

static int sixpack_receive_room(struct tty_struct *tty)
{
	return 65536;  /* We can handle an infinite amount of data. :-) */
}

/*
 * Handle the 'receiver data ready' interrupt.
 * This function is called by the 'tty_io' module in the kernel when
 * a block of 6pack data has been received, which can now be decapsulated
 * and sent on to some IP layer for further processing.
 */
static void sixpack_receive_buf(struct tty_struct *tty,
	const unsigned char *cp, char *fp, int count)
{
	struct sixpack *sp;
	unsigned char buf[512];
	int count1;

	if (!count)
		return;

	sp = sp_get(tty);
	if (!sp)
		return;

	memcpy(buf, cp, count < sizeof(buf) ? count : sizeof(buf));

	/* Read the characters out of the buffer */

	count1 = count;
	while (count) {
		count--;
		if (fp && *fp++) {
			if (!test_and_set_bit(SIXPF_ERROR, &sp->flags))
				sp->stats.rx_errors++;
			continue;
		}
	}
	sixpack_decode(sp, buf, count1);

	sp_put(sp);
	if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
	    && tty->driver->unthrottle)
		tty->driver->unthrottle(tty);
}

/*
 * Try to resync the TNC. Called by the resync timer defined in
 * decode_prio_command
 */

#define TNC_UNINITIALIZED	0
#define TNC_UNSYNC_STARTUP	1
#define TNC_UNSYNCED		2
#define TNC_IN_SYNC		3

static void __tnc_set_sync_state(struct sixpack *sp, int new_tnc_state)
{
	char *msg;