ppp_synctty.c

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/*
 * PPP synchronous tty channel driver for Linux.
 *
 * This is a ppp channel driver that can be used with tty device drivers
 * that are frame oriented, such as synchronous HDLC devices.
 *
 * Complete PPP frames without encoding/decoding are exchanged between
 * the channel driver and the device driver.
 *
 * The async map IOCTL codes are implemented to keep the user mode
 * applications happy if they call them. Synchronous PPP does not use
 * the async maps.
 *
 * Copyright 1999 Paul Mackerras.
 *
 * Also touched by the grubby hands of Paul Fulghum [e-mail]
 *
 *  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 driver provides the encapsulation and framing for sending
 * and receiving PPP frames over sync serial lines.  It relies on
 * the generic PPP layer to give it frames to send and to process
 * received frames.  It implements the PPP line discipline.
 *
 * Part of the code in this driver was inspired by the old async-only
 * PPP driver, written by Michael Callahan and Al Longyear, and
 * subsequently hacked by Paul Mackerras.
 *
 * ==FILEVERSION 20040616==
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/tty.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/ppp_defs.h>
#include <linux/if_ppp.h>
#include <linux/ppp_channel.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <asm/uaccess.h>
#include <asm/semaphore.h>

#define PPP_VERSION	"2.4.2"

/* Structure for storing local state. */
struct syncppp {
	struct tty_struct *tty;
	unsigned int	flags;
	unsigned int	rbits;
	int		mru;
	spinlock_t	xmit_lock;
	spinlock_t	recv_lock;
	unsigned long	xmit_flags;
	u32		xaccm[8];
	u32		raccm;
	unsigned int	bytes_sent;
	unsigned int	bytes_rcvd;

	struct sk_buff	*tpkt;
	unsigned long	last_xmit;

	struct sk_buff_head rqueue;

	struct tasklet_struct tsk;

	atomic_t	refcnt;
	struct semaphore dead_sem;
	struct ppp_channel chan;	/* interface to generic ppp layer */
};

/* Bit numbers in xmit_flags */
#define XMIT_WAKEUP	0
#define XMIT_FULL	1

/* Bits in rbits */
#define SC_RCV_BITS	(SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)

#define PPPSYNC_MAX_RQLEN	32	/* arbitrary */

/*
 * Prototypes.
 */
static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
			  unsigned long arg);
static void ppp_sync_process(unsigned long arg);
static int ppp_sync_push(struct syncppp *ap);
static void ppp_sync_flush_output(struct syncppp *ap);
static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
			   char *flags, int count);

static struct ppp_channel_ops sync_ops = {
	ppp_sync_send,
	ppp_sync_ioctl
};

/*
 * Utility procedures to print a buffer in hex/ascii
 */
static void
ppp_print_hex (register __u8 * out, const __u8 * in, int count)
{
	register __u8 next_ch;
	static const char hex[] = "0123456789ABCDEF";

	while (count-- > 0) {
		next_ch = *in++;
		*out++ = hex[(next_ch >> 4) & 0x0F];
		*out++ = hex[next_ch & 0x0F];
		++out;
	}
}

static void
ppp_print_char (register __u8 * out, const __u8 * in, int count)
{
	register __u8 next_ch;

	while (count-- > 0) {
		next_ch = *in++;

		if (next_ch < 0x20 || next_ch > 0x7e)
			*out++ = '.';
		else {
			*out++ = next_ch;
			if (next_ch == '%')   /* printk/syslogd has a bug !! */
				*out++ = '%';
		}
	}
	*out = '\0';
}

static void
ppp_print_buffer (const char *name, const __u8 *buf, int count)
{
	__u8 line[44];

	if (name != NULL)
		printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);

	while (count > 8) {
		memset (line, 32, 44);
		ppp_print_hex (line, buf, 8);
		ppp_print_char (&line[8 * 3], buf, 8);
		printk(KERN_DEBUG "%s\n", line);
		count -= 8;
		buf += 8;
	}

	if (count > 0) {
		memset (line, 32, 44);
		ppp_print_hex (line, buf, count);
		ppp_print_char (&line[8 * 3], buf, count);
		printk(KERN_DEBUG "%s\n", line);
	}
}


/*
 * Routines implementing the synchronous PPP line discipline.
 */

/*
 * 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 ppp_synctty_receive while another
 * calls ppp_synctty_close, which zeroes tty->disc_data and
 * frees the memory that ppp_synctty_receive 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.
 *
 * FIXME: Fixed in tty_io nowdays.
 */
static DEFINE_RWLOCK(disc_data_lock);

static struct syncppp *sp_get(struct tty_struct *tty)
{
	struct syncppp *ap;

	read_lock(&disc_data_lock);
	ap = tty->disc_data;
	if (ap != NULL)
		atomic_inc(&ap->refcnt);
	read_unlock(&disc_data_lock);
	return ap;
}

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

/*
 * Called when a tty is put into sync-PPP line discipline.
 */
static int
ppp_sync_open(struct tty_struct *tty)
{
	struct syncppp *ap;
	int err;

	ap = kzalloc(sizeof(*ap), GFP_KERNEL);
	err = -ENOMEM;
	if (!ap)
		goto out;

	/* initialize the syncppp structure */
	ap->tty = tty;
	ap->mru = PPP_MRU;
	spin_lock_init(&ap->xmit_lock);
	spin_lock_init(&ap->recv_lock);
	ap->xaccm[0] = ~0U;
	ap->xaccm[3] = 0x60000000U;
	ap->raccm = ~0U;

	skb_queue_head_init(&ap->rqueue);
	tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);

	atomic_set(&ap->refcnt, 1);
	init_MUTEX_LOCKED(&ap->dead_sem);

	ap->chan.private = ap;
	ap->chan.ops = &sync_ops;
	ap->chan.mtu = PPP_MRU;
	ap->chan.hdrlen = 2;	/* for A/C bytes */
	err = ppp_register_channel(&ap->chan);
	if (err)
		goto out_free;

	tty->disc_data = ap;
	tty->receive_room = 65536;
	return 0;

 out_free:
	kfree(ap);
 out:
	return err;
}

/*
 * Called when the tty is put into another line discipline
 * or it hangs up.  We have to wait for any cpu currently
 * executing in any of the other ppp_synctty_* routines to
 * finish before we can call ppp_unregister_channel and free
 * the syncppp struct.  This routine must be called from
 * process context, not interrupt or softirq context.
 */
static void
ppp_sync_close(struct tty_struct *tty)
{
	struct syncppp *ap;

	write_lock_irq(&disc_data_lock);
	ap = tty->disc_data;
	tty->disc_data = NULL;
	write_unlock_irq(&disc_data_lock);
	if (!ap)
		return;

	/*
	 * We have now ensured that nobody can start using ap from now
	 * on, but we have to wait for all existing users to finish.
	 * Note that ppp_unregister_channel ensures that no calls to
	 * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
	 * by the time it returns.
	 */
	if (!atomic_dec_and_test(&ap->refcnt))
		down(&ap->dead_sem);
	tasklet_kill(&ap->tsk);

	ppp_unregister_channel(&ap->chan);
	skb_queue_purge(&ap->rqueue);
	if (ap->tpkt)
		kfree_skb(ap->tpkt);
	kfree(ap);
}

/*
 * Called on tty hangup in process context.
 *
 * Wait for I/O to driver to complete and unregister PPP channel.
 * This is already done by the close routine, so just call that.
 */
static int ppp_sync_hangup(struct tty_struct *tty)
{
	ppp_sync_close(tty);
	return 0;
}

/*
 * Read does nothing - no data is ever available this way.
 * Pppd reads and writes packets via /dev/ppp instead.
 */
static ssize_t
ppp_sync_read(struct tty_struct *tty, struct file *file,
	       unsigned char __user *buf, size_t count)
{
	return -EAGAIN;
}

/*
 * Write on the tty does nothing, the packets all come in
 * from the ppp generic stuff.
 */
static ssize_t
ppp_sync_write(struct tty_struct *tty, struct file *file,
		const unsigned char *buf, size_t count)
{
	return -EAGAIN;
}

static int
ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
		  unsigned int cmd, unsigned long arg)
{
	struct syncppp *ap = sp_get(tty);
	int __user *p = (int __user *)arg;
	int err, val;

	if (!ap)
		return -ENXIO;
	err = -EFAULT;
	switch (cmd) {
	case PPPIOCGCHAN:
		err = -ENXIO;
		if (!ap)
			break;
		err = -EFAULT;
		if (put_user(ppp_channel_index(&ap->chan), p))
			break;
		err = 0;
		break;

	case PPPIOCGUNIT:
		err = -ENXIO;
		if (!ap)
			break;
		err = -EFAULT;
		if (put_user(ppp_unit_number(&ap->chan), p))
			break;
		err = 0;
		break;

	case TCFLSH:
		/* flush our buffers and the serial port's buffer */
		if (arg == TCIOFLUSH || arg == TCOFLUSH)
			ppp_sync_flush_output(ap);
		err = tty_perform_flush(tty, arg);
		break;

	case FIONREAD:
		val = 0;
		if (put_user(val, p))
			break;
		err = 0;
		break;

	default:
		err = tty_mode_ioctl(tty, file, cmd, arg);
		break;
	}

	sp_put(ap);
	return err;
}

/* No kernel lock - fine */
static unsigned int
ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
{
	return 0;
}

/*
 * This can now be called from hard interrupt level as well
 * as soft interrupt level or mainline.
 */
static void
ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
		  char *cflags, int count)
{
	struct syncppp *ap = sp_get(tty);
	unsigned long flags;

	if (!ap)
		return;
	spin_lock_irqsave(&ap->recv_lock, flags);
	ppp_sync_input(ap, buf, cflags, count);
	spin_unlock_irqrestore(&ap->recv_lock, flags);