Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
diff --git a/drivers/net/ppp_synctty.c b/drivers/net/ppp_synctty.c
new file mode 100644
index 0000000..7d0150b
--- /dev/null
+++ b/drivers/net/ppp_synctty.c
@@ -0,0 +1,803 @@
+/*
+ * 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 paulkf@microgate.com
+ *
+ * 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 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 = kmalloc(sizeof(*ap), GFP_KERNEL);
+ err = -ENOMEM;
+ if (ap == 0)
+ goto out;
+
+ /* initialize the syncppp structure */
+ memset(ap, 0, sizeof(*ap));
+ 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;
+
+ 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 == 0)
+ 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 != 0)
+ 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 == 0)
+ return -ENXIO;
+ err = -EFAULT;
+ switch (cmd) {
+ case PPPIOCGCHAN:
+ err = -ENXIO;
+ if (ap == 0)
+ break;
+ err = -EFAULT;
+ if (put_user(ppp_channel_index(&ap->chan), p))
+ break;
+ err = 0;
+ break;
+
+ case PPPIOCGUNIT:
+ err = -ENXIO;
+ if (ap == 0)
+ break;
+ err = -EFAULT;
+ if (put_user(ppp_unit_number(&ap->chan), p))
+ break;
+ err = 0;
+ break;
+
+ case TCGETS:
+ case TCGETA:
+ err = n_tty_ioctl(tty, file, cmd, arg);
+ break;
+
+ case TCFLSH:
+ /* flush our buffers and the serial port's buffer */
+ if (arg == TCIOFLUSH || arg == TCOFLUSH)
+ ppp_sync_flush_output(ap);
+ err = n_tty_ioctl(tty, file, cmd, arg);
+ break;
+
+ case FIONREAD:
+ val = 0;
+ if (put_user(val, p))
+ break;
+ err = 0;
+ break;
+
+ default:
+ err = -ENOIOCTLCMD;
+ }
+
+ 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;
+}
+
+static int
+ppp_sync_room(struct tty_struct *tty)
+{
+ return 65535;
+}
+
+/*
+ * 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 == 0)
+ return;
+ spin_lock_irqsave(&ap->recv_lock, flags);
+ ppp_sync_input(ap, buf, cflags, count);
+ spin_unlock_irqrestore(&ap->recv_lock, flags);
+ if (skb_queue_len(&ap->rqueue))
+ tasklet_schedule(&ap->tsk);
+ sp_put(ap);
+ if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
+ && tty->driver->unthrottle)
+ tty->driver->unthrottle(tty);
+}
+
+static void
+ppp_sync_wakeup(struct tty_struct *tty)
+{
+ struct syncppp *ap = sp_get(tty);
+
+ clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+ if (ap == 0)
+ return;
+ set_bit(XMIT_WAKEUP, &ap->xmit_flags);
+ tasklet_schedule(&ap->tsk);
+ sp_put(ap);
+}
+
+
+static struct tty_ldisc ppp_sync_ldisc = {
+ .owner = THIS_MODULE,
+ .magic = TTY_LDISC_MAGIC,
+ .name = "pppsync",
+ .open = ppp_sync_open,
+ .close = ppp_sync_close,
+ .hangup = ppp_sync_hangup,
+ .read = ppp_sync_read,
+ .write = ppp_sync_write,
+ .ioctl = ppp_synctty_ioctl,
+ .poll = ppp_sync_poll,
+ .receive_room = ppp_sync_room,
+ .receive_buf = ppp_sync_receive,
+ .write_wakeup = ppp_sync_wakeup,
+};
+
+static int __init
+ppp_sync_init(void)
+{
+ int err;
+
+ err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
+ if (err != 0)
+ printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
+ err);
+ return err;
+}
+
+/*
+ * The following routines provide the PPP channel interface.
+ */
+static int
+ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
+{
+ struct syncppp *ap = chan->private;
+ int err, val;
+ u32 accm[8];
+ void __user *argp = (void __user *)arg;
+ u32 __user *p = argp;
+
+ err = -EFAULT;
+ switch (cmd) {
+ case PPPIOCGFLAGS:
+ val = ap->flags | ap->rbits;
+ if (put_user(val, (int __user *) argp))
+ break;
+ err = 0;
+ break;
+ case PPPIOCSFLAGS:
+ if (get_user(val, (int __user *) argp))
+ break;
+ ap->flags = val & ~SC_RCV_BITS;
+ spin_lock_irq(&ap->recv_lock);
+ ap->rbits = val & SC_RCV_BITS;
+ spin_unlock_irq(&ap->recv_lock);
+ err = 0;
+ break;
+
+ case PPPIOCGASYNCMAP:
+ if (put_user(ap->xaccm[0], p))
+ break;
+ err = 0;
+ break;
+ case PPPIOCSASYNCMAP:
+ if (get_user(ap->xaccm[0], p))
+ break;
+ err = 0;
+ break;
+
+ case PPPIOCGRASYNCMAP:
+ if (put_user(ap->raccm, p))
+ break;
+ err = 0;
+ break;
+ case PPPIOCSRASYNCMAP:
+ if (get_user(ap->raccm, p))
+ break;
+ err = 0;
+ break;
+
+ case PPPIOCGXASYNCMAP:
+ if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
+ break;
+ err = 0;
+ break;
+ case PPPIOCSXASYNCMAP:
+ if (copy_from_user(accm, argp, sizeof(accm)))
+ break;
+ accm[2] &= ~0x40000000U; /* can't escape 0x5e */
+ accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */
+ memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
+ err = 0;
+ break;
+
+ case PPPIOCGMRU:
+ if (put_user(ap->mru, (int __user *) argp))
+ break;
+ err = 0;
+ break;
+ case PPPIOCSMRU:
+ if (get_user(val, (int __user *) argp))
+ break;
+ if (val < PPP_MRU)
+ val = PPP_MRU;
+ ap->mru = val;
+ err = 0;
+ break;
+
+ default:
+ err = -ENOTTY;
+ }
+ return err;
+}
+
+/*
+ * This is called at softirq level to deliver received packets
+ * to the ppp_generic code, and to tell the ppp_generic code
+ * if we can accept more output now.
+ */
+static void ppp_sync_process(unsigned long arg)
+{
+ struct syncppp *ap = (struct syncppp *) arg;
+ struct sk_buff *skb;
+
+ /* process received packets */
+ while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
+ if (skb->len == 0) {
+ /* zero length buffers indicate error */
+ ppp_input_error(&ap->chan, 0);
+ kfree_skb(skb);
+ }
+ else
+ ppp_input(&ap->chan, skb);
+ }
+
+ /* try to push more stuff out */
+ if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
+ ppp_output_wakeup(&ap->chan);
+}
+
+/*
+ * Procedures for encapsulation and framing.
+ */
+
+struct sk_buff*
+ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
+{
+ int proto;
+ unsigned char *data;
+ int islcp;
+
+ data = skb->data;
+ proto = (data[0] << 8) + data[1];
+
+ /* LCP packets with codes between 1 (configure-request)
+ * and 7 (code-reject) must be sent as though no options
+ * have been negotiated.
+ */
+ islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
+
+ /* compress protocol field if option enabled */
+ if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
+ skb_pull(skb,1);
+
+ /* prepend address/control fields if necessary */
+ if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
+ if (skb_headroom(skb) < 2) {
+ struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
+ if (npkt == NULL) {
+ kfree_skb(skb);
+ return NULL;
+ }
+ skb_reserve(npkt,2);
+ memcpy(skb_put(npkt,skb->len), skb->data, skb->len);
+ kfree_skb(skb);
+ skb = npkt;
+ }
+ skb_push(skb,2);
+ skb->data[0] = PPP_ALLSTATIONS;
+ skb->data[1] = PPP_UI;
+ }
+
+ ap->last_xmit = jiffies;
+
+ if (skb && ap->flags & SC_LOG_OUTPKT)
+ ppp_print_buffer ("send buffer", skb->data, skb->len);
+
+ return skb;
+}
+
+/*
+ * Transmit-side routines.
+ */
+
+/*
+ * Send a packet to the peer over an sync tty line.
+ * Returns 1 iff the packet was accepted.
+ * If the packet was not accepted, we will call ppp_output_wakeup
+ * at some later time.
+ */
+static int
+ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
+{
+ struct syncppp *ap = chan->private;
+
+ ppp_sync_push(ap);
+
+ if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
+ return 0; /* already full */
+ skb = ppp_sync_txmunge(ap, skb);
+ if (skb != NULL)
+ ap->tpkt = skb;
+ else
+ clear_bit(XMIT_FULL, &ap->xmit_flags);
+
+ ppp_sync_push(ap);
+ return 1;
+}
+
+/*
+ * Push as much data as possible out to the tty.
+ */
+static int
+ppp_sync_push(struct syncppp *ap)
+{
+ int sent, done = 0;
+ struct tty_struct *tty = ap->tty;
+ int tty_stuffed = 0;
+
+ if (!spin_trylock_bh(&ap->xmit_lock))
+ return 0;
+ for (;;) {
+ if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
+ tty_stuffed = 0;
+ if (!tty_stuffed && ap->tpkt != 0) {
+ set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+ sent = tty->driver->write(tty, ap->tpkt->data, ap->tpkt->len);
+ if (sent < 0)
+ goto flush; /* error, e.g. loss of CD */
+ if (sent < ap->tpkt->len) {
+ tty_stuffed = 1;
+ } else {
+ kfree_skb(ap->tpkt);
+ ap->tpkt = NULL;
+ clear_bit(XMIT_FULL, &ap->xmit_flags);
+ done = 1;
+ }
+ continue;
+ }
+ /* haven't made any progress */
+ spin_unlock_bh(&ap->xmit_lock);
+ if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
+ || (!tty_stuffed && ap->tpkt != 0)))
+ break;
+ if (!spin_trylock_bh(&ap->xmit_lock))
+ break;
+ }
+ return done;
+
+flush:
+ if (ap->tpkt != 0) {
+ kfree_skb(ap->tpkt);
+ ap->tpkt = NULL;
+ clear_bit(XMIT_FULL, &ap->xmit_flags);
+ done = 1;
+ }
+ spin_unlock_bh(&ap->xmit_lock);
+ return done;
+}
+
+/*
+ * Flush output from our internal buffers.
+ * Called for the TCFLSH ioctl.
+ */
+static void
+ppp_sync_flush_output(struct syncppp *ap)
+{
+ int done = 0;
+
+ spin_lock_bh(&ap->xmit_lock);
+ if (ap->tpkt != NULL) {
+ kfree_skb(ap->tpkt);
+ ap->tpkt = NULL;
+ clear_bit(XMIT_FULL, &ap->xmit_flags);
+ done = 1;
+ }
+ spin_unlock_bh(&ap->xmit_lock);
+ if (done)
+ ppp_output_wakeup(&ap->chan);
+}
+
+/*
+ * Receive-side routines.
+ */
+
+/* called when the tty driver has data for us.
+ *
+ * Data is frame oriented: each call to ppp_sync_input is considered
+ * a whole frame. If the 1st flag byte is non-zero then the whole
+ * frame is considered to be in error and is tossed.
+ */
+static void
+ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
+ char *flags, int count)
+{
+ struct sk_buff *skb;
+ unsigned char *p;
+
+ if (count == 0)
+ return;
+
+ if (ap->flags & SC_LOG_INPKT)
+ ppp_print_buffer ("receive buffer", buf, count);
+
+ /* stuff the chars in the skb */
+ if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
+ printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
+ goto err;
+ }
+ /* Try to get the payload 4-byte aligned */
+ if (buf[0] != PPP_ALLSTATIONS)
+ skb_reserve(skb, 2 + (buf[0] & 1));
+
+ if (flags != 0 && *flags) {
+ /* error flag set, ignore frame */
+ goto err;
+ } else if (count > skb_tailroom(skb)) {
+ /* packet overflowed MRU */
+ goto err;
+ }
+
+ p = skb_put(skb, count);
+ memcpy(p, buf, count);
+
+ /* strip address/control field if present */
+ p = skb->data;
+ if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
+ /* chop off address/control */
+ if (skb->len < 3)
+ goto err;
+ p = skb_pull(skb, 2);
+ }
+
+ /* decompress protocol field if compressed */
+ if (p[0] & 1) {
+ /* protocol is compressed */
+ skb_push(skb, 1)[0] = 0;
+ } else if (skb->len < 2)
+ goto err;
+
+ /* queue the frame to be processed */
+ skb_queue_tail(&ap->rqueue, skb);
+ return;
+
+err:
+ /* queue zero length packet as error indication */
+ if (skb || (skb = dev_alloc_skb(0))) {
+ skb_trim(skb, 0);
+ skb_queue_tail(&ap->rqueue, skb);
+ }
+}
+
+static void __exit
+ppp_sync_cleanup(void)
+{
+ if (tty_register_ldisc(N_SYNC_PPP, NULL) != 0)
+ printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
+}
+
+module_init(ppp_sync_init);
+module_exit(ppp_sync_cleanup);
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_LDISC(N_SYNC_PPP);