path: root/drivers/net/ppp_async.c

/*
 * PPP async serial channel driver for Linux.
 *
 * Copyright 1999 Paul Mackerras.
 *
 *  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 async 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.
 */

#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/crc-ccitt.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 <linux/jiffies.h>
#include <asm/uaccess.h>
#include <asm/string.h>

#define PPP_VERSION	"2.4.2"

#define OBUFSIZE	4096

/* Structure for storing local state. */
struct asyncppp {
	struct tty_struct *tty;
	unsigned int	flags;
	unsigned int	state;
	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;
	int		tpkt_pos;
	u16		tfcs;
	unsigned char	*optr;
	unsigned char	*olim;
	unsigned long	last_xmit;

	struct sk_buff	*rpkt;
	int		lcp_fcs;
	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 */
	unsigned char	obuf[OBUFSIZE];
};

/* Bit numbers in xmit_flags */
#define XMIT_WAKEUP	0
#define XMIT_FULL	1
#define XMIT_BUSY	2

/* State bits */
#define SC_TOSS		1
#define SC_ESCAPE	2
#define SC_PREV_ERROR	4

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

static int flag_time = HZ;
module_param(flag_time, int, 0);
MODULE_PARM_DESC(flag_time, "ppp_async: interval between flagged packets (in clock ticks)");
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_PPP);

/*
 * Prototypes.
 */
static int ppp_async_encode(struct asyncppp *ap);
static int ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb);
static int ppp_async_push(struct asyncppp *ap);
static void ppp_async_flush_output(struct asyncppp *ap);
static void ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
			    char *flags, int count);
static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
			   unsigned long arg);
static void ppp_async_process(unsigned long arg);

static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
			   int len, int inbound);

static struct ppp_channel_ops async_ops = {
	ppp_async_send,
	ppp_async_ioctl
};

/*
 * Routines implementing the 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_asynctty_receive while another
 * calls ppp_asynctty_close, which zeroes tty->disc_data and
 * frees the memory that ppp_asynctty_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: this is no longer true. The _close path for the ldisc is
 * now guaranteed to be sane.
 */
static DEFINE_RWLOCK(disc_data_lock);

static struct asyncppp *ap_get(struct tty_struct *tty)
{
	struct asyncppp *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 ap_put(struct asyncppp *ap)
{
	if (atomic_dec_and_test(&ap->refcnt))
		up(&ap->dead_sem);
}

/*
 * Called when a tty is put into PPP line discipline. Called in process
 * context.
 */
static int
ppp_asynctty_open(struct tty_struct *tty)
{
	struct asyncppp *ap;
	int err;
	int speed;

	if (tty->ops->write == NULL)
		return -EOPNOTSUPP;

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

	/* initialize the asyncppp 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;