2 * PPP async serial channel driver for Linux.
4 * Copyright 1999 Paul Mackerras.
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
11 * This driver provides the encapsulation and framing for sending
12 * and receiving PPP frames over async serial lines. It relies on
13 * the generic PPP layer to give it frames to send and to process
14 * received frames. It implements the PPP line discipline.
16 * Part of the code in this driver was inspired by the old async-only
17 * PPP driver, written by Michael Callahan and Al Longyear, and
18 * subsequently hacked by Paul Mackerras.
21 #include <linux/module.h>
22 #include <linux/kernel.h>
23 #include <linux/skbuff.h>
24 #include <linux/tty.h>
25 #include <linux/netdevice.h>
26 #include <linux/poll.h>
27 #include <linux/crc-ccitt.h>
28 #include <linux/ppp_defs.h>
29 #include <linux/if_ppp.h>
30 #include <linux/ppp_channel.h>
31 #include <linux/spinlock.h>
32 #include <linux/init.h>
33 #include <asm/uaccess.h>
35 #define PPP_VERSION "2.4.2"
39 /* Structure for storing local state. */
41 struct tty_struct *tty;
48 unsigned long xmit_flags;
51 unsigned int bytes_sent;
52 unsigned int bytes_rcvd;
59 unsigned long last_xmit;
63 struct sk_buff_head rqueue;
65 struct tasklet_struct tsk;
68 struct semaphore dead_sem;
69 struct ppp_channel chan; /* interface to generic ppp layer */
70 unsigned char obuf[OBUFSIZE];
73 /* Bit numbers in xmit_flags */
81 #define SC_PREV_ERROR 4
84 #define SC_RCV_BITS (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
86 static int flag_time = HZ;
87 MODULE_PARM(flag_time, "i");
88 MODULE_PARM_DESC(flag_time, "ppp_async: interval between flagged packets (in clock ticks)");
89 MODULE_LICENSE("GPL");
90 MODULE_ALIAS_LDISC(N_PPP);
95 static int ppp_async_encode(struct asyncppp *ap);
96 static int ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb);
97 static int ppp_async_push(struct asyncppp *ap);
98 static void ppp_async_flush_output(struct asyncppp *ap);
99 static void ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
100 char *flags, int count);
101 static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
103 static void ppp_async_process(unsigned long arg);
105 static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
106 int len, int inbound);
108 static struct ppp_channel_ops async_ops = {
114 * Routines implementing the PPP line discipline.
118 * We have a potential race on dereferencing tty->disc_data,
119 * because the tty layer provides no locking at all - thus one
120 * cpu could be running ppp_asynctty_receive while another
121 * calls ppp_asynctty_close, which zeroes tty->disc_data and
122 * frees the memory that ppp_asynctty_receive is using. The best
123 * way to fix this is to use a rwlock in the tty struct, but for now
124 * we use a single global rwlock for all ttys in ppp line discipline.
126 static rwlock_t disc_data_lock = RW_LOCK_UNLOCKED;
128 static struct asyncppp *ap_get(struct tty_struct *tty)
132 read_lock(&disc_data_lock);
135 atomic_inc(&ap->refcnt);
136 read_unlock(&disc_data_lock);
140 static void ap_put(struct asyncppp *ap)
142 if (atomic_dec_and_test(&ap->refcnt))
147 * Called when a tty is put into PPP line discipline.
150 ppp_asynctty_open(struct tty_struct *tty)
156 ap = kmalloc(sizeof(*ap), GFP_KERNEL);
160 /* initialize the asyncppp structure */
161 memset(ap, 0, sizeof(*ap));
164 spin_lock_init(&ap->xmit_lock);
165 spin_lock_init(&ap->recv_lock);
167 ap->xaccm[3] = 0x60000000U;
173 skb_queue_head_init(&ap->rqueue);
174 tasklet_init(&ap->tsk, ppp_async_process, (unsigned long) ap);
176 atomic_set(&ap->refcnt, 1);
177 init_MUTEX_LOCKED(&ap->dead_sem);
179 ap->chan.private = ap;
180 ap->chan.ops = &async_ops;
181 ap->chan.mtu = PPP_MRU;
182 err = ppp_register_channel(&ap->chan);
197 * Called when the tty is put into another line discipline
198 * or it hangs up. We have to wait for any cpu currently
199 * executing in any of the other ppp_asynctty_* routines to
200 * finish before we can call ppp_unregister_channel and free
201 * the asyncppp struct. This routine must be called from
202 * process context, not interrupt or softirq context.
205 ppp_asynctty_close(struct tty_struct *tty)
209 write_lock_irq(&disc_data_lock);
211 tty->disc_data = NULL;
212 write_unlock_irq(&disc_data_lock);
217 * We have now ensured that nobody can start using ap from now
218 * on, but we have to wait for all existing users to finish.
219 * Note that ppp_unregister_channel ensures that no calls to
220 * our channel ops (i.e. ppp_async_send/ioctl) are in progress
221 * by the time it returns.
223 if (!atomic_dec_and_test(&ap->refcnt))
225 tasklet_kill(&ap->tsk);
227 ppp_unregister_channel(&ap->chan);
230 skb_queue_purge(&ap->rqueue);
237 * Read does nothing - no data is ever available this way.
238 * Pppd reads and writes packets via /dev/ppp instead.
241 ppp_asynctty_read(struct tty_struct *tty, struct file *file,
242 unsigned char __user *buf, size_t count)
248 * Write on the tty does nothing, the packets all come in
249 * from the ppp generic stuff.
252 ppp_asynctty_write(struct tty_struct *tty, struct file *file,
253 const unsigned char __user *buf, size_t count)
259 ppp_asynctty_ioctl(struct tty_struct *tty, struct file *file,
260 unsigned int cmd, unsigned long arg)
262 struct asyncppp *ap = ap_get(tty);
264 int __user *p = (int __user *)arg;
275 if (put_user(ppp_channel_index(&ap->chan), p))
285 if (put_user(ppp_unit_number(&ap->chan), p))
292 err = n_tty_ioctl(tty, file, cmd, arg);
296 /* flush our buffers and the serial port's buffer */
297 if (arg == TCIOFLUSH || arg == TCOFLUSH)
298 ppp_async_flush_output(ap);
299 err = n_tty_ioctl(tty, file, cmd, arg);
304 if (put_user(val, p))
317 /* No kernel lock - fine */
319 ppp_asynctty_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
325 ppp_asynctty_room(struct tty_struct *tty)
331 * This can now be called from hard interrupt level as well
332 * as soft interrupt level or mainline.
335 ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
336 char *cflags, int count)
338 struct asyncppp *ap = ap_get(tty);
343 spin_lock_irqsave(&ap->recv_lock, flags);
344 ppp_async_input(ap, buf, cflags, count);
345 spin_unlock_irqrestore(&ap->recv_lock, flags);
346 if (skb_queue_len(&ap->rqueue))
347 tasklet_schedule(&ap->tsk);
349 if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
350 && tty->driver->unthrottle)
351 tty->driver->unthrottle(tty);
355 ppp_asynctty_wakeup(struct tty_struct *tty)
357 struct asyncppp *ap = ap_get(tty);
359 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
362 set_bit(XMIT_WAKEUP, &ap->xmit_flags);
363 tasklet_schedule(&ap->tsk);
368 static struct tty_ldisc ppp_ldisc = {
369 .owner = THIS_MODULE,
370 .magic = TTY_LDISC_MAGIC,
372 .open = ppp_asynctty_open,
373 .close = ppp_asynctty_close,
374 .read = ppp_asynctty_read,
375 .write = ppp_asynctty_write,
376 .ioctl = ppp_asynctty_ioctl,
377 .poll = ppp_asynctty_poll,
378 .receive_room = ppp_asynctty_room,
379 .receive_buf = ppp_asynctty_receive,
380 .write_wakeup = ppp_asynctty_wakeup,
388 err = tty_register_ldisc(N_PPP, &ppp_ldisc);
390 printk(KERN_ERR "PPP_async: error %d registering line disc.\n",
396 * The following routines provide the PPP channel interface.
399 ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
401 struct asyncppp *ap = chan->private;
402 void __user *argp = (void __user *)arg;
403 int __user *p = argp;
410 val = ap->flags | ap->rbits;
411 if (put_user(val, p))
416 if (get_user(val, p))
418 ap->flags = val & ~SC_RCV_BITS;
419 spin_lock_irq(&ap->recv_lock);
420 ap->rbits = val & SC_RCV_BITS;
421 spin_unlock_irq(&ap->recv_lock);
425 case PPPIOCGASYNCMAP:
426 if (put_user(ap->xaccm[0], (u32 __user *)argp))
430 case PPPIOCSASYNCMAP:
431 if (get_user(ap->xaccm[0], (u32 __user *)argp))
436 case PPPIOCGRASYNCMAP:
437 if (put_user(ap->raccm, (u32 __user *)argp))
441 case PPPIOCSRASYNCMAP:
442 if (get_user(ap->raccm, (u32 __user *)argp))
447 case PPPIOCGXASYNCMAP:
448 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
452 case PPPIOCSXASYNCMAP:
453 if (copy_from_user(accm, argp, sizeof(accm)))
455 accm[2] &= ~0x40000000U; /* can't escape 0x5e */
456 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */
457 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
462 if (put_user(ap->mru, p))
467 if (get_user(val, p))
483 * This is called at softirq level to deliver received packets
484 * to the ppp_generic code, and to tell the ppp_generic code
485 * if we can accept more output now.
487 static void ppp_async_process(unsigned long arg)
489 struct asyncppp *ap = (struct asyncppp *) arg;
492 /* process received packets */
493 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
495 ppp_input_error(&ap->chan, 0);
496 ppp_input(&ap->chan, skb);
499 /* try to push more stuff out */
500 if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_async_push(ap))
501 ppp_output_wakeup(&ap->chan);
505 * Procedures for encapsulation and framing.
509 * Procedure to encode the data for async serial transmission.
510 * Does octet stuffing (escaping), puts the address/control bytes
511 * on if A/C compression is disabled, and does protocol compression.
512 * Assumes ap->tpkt != 0 on entry.
513 * Returns 1 if we finished the current frame, 0 otherwise.
516 #define PUT_BYTE(ap, buf, c, islcp) do { \
517 if ((islcp && c < 0x20) || (ap->xaccm[c >> 5] & (1 << (c & 0x1f)))) {\
518 *buf++ = PPP_ESCAPE; \
525 ppp_async_encode(struct asyncppp *ap)
527 int fcs, i, count, c, proto;
528 unsigned char *buf, *buflim;
536 data = ap->tpkt->data;
537 count = ap->tpkt->len;
539 proto = (data[0] << 8) + data[1];
542 * LCP packets with code values between 1 (configure-reqest)
543 * and 7 (code-reject) must be sent as though no options
544 * had been negotiated.
546 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
550 async_lcp_peek(ap, data, count, 0);
553 * Start of a new packet - insert the leading FLAG
554 * character if necessary.
556 if (islcp || flag_time == 0
557 || jiffies - ap->last_xmit >= flag_time)
559 ap->last_xmit = jiffies;
563 * Put in the address/control bytes if necessary
565 if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
566 PUT_BYTE(ap, buf, 0xff, islcp);
567 fcs = PPP_FCS(fcs, 0xff);
568 PUT_BYTE(ap, buf, 0x03, islcp);
569 fcs = PPP_FCS(fcs, 0x03);
574 * Once we put in the last byte, we need to put in the FCS
575 * and closing flag, so make sure there is at least 7 bytes
576 * of free space in the output buffer.
578 buflim = ap->obuf + OBUFSIZE - 6;
579 while (i < count && buf < buflim) {
581 if (i == 1 && c == 0 && (ap->flags & SC_COMP_PROT))
582 continue; /* compress protocol field */
583 fcs = PPP_FCS(fcs, c);
584 PUT_BYTE(ap, buf, c, islcp);
589 * Remember where we are up to in this packet.
598 * We have finished the packet. Add the FCS and flag.
602 PUT_BYTE(ap, buf, c, islcp);
603 c = (fcs >> 8) & 0xff;
604 PUT_BYTE(ap, buf, c, islcp);
614 * Transmit-side routines.
618 * Send a packet to the peer over an async tty line.
619 * Returns 1 iff the packet was accepted.
620 * If the packet was not accepted, we will call ppp_output_wakeup
621 * at some later time.
624 ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb)
626 struct asyncppp *ap = chan->private;
630 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
631 return 0; /* already full */
640 * Push as much data as possible out to the tty.
643 ppp_async_push(struct asyncppp *ap)
645 int avail, sent, done = 0;
646 struct tty_struct *tty = ap->tty;
650 * We can get called recursively here if the tty write
651 * function calls our wakeup function. This can happen
652 * for example on a pty with both the master and slave
653 * set to PPP line discipline.
654 * We use the XMIT_BUSY bit to detect this and get out,
655 * leaving the XMIT_WAKEUP bit set to tell the other
656 * instance that it may now be able to write more now.
658 if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
660 spin_lock_bh(&ap->xmit_lock);
662 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
664 if (!tty_stuffed && ap->optr < ap->olim) {
665 avail = ap->olim - ap->optr;
666 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
667 sent = tty->driver->write(tty, 0, ap->optr, avail);
669 goto flush; /* error, e.g. loss of CD */
675 if (ap->optr >= ap->olim && ap->tpkt != 0) {
676 if (ppp_async_encode(ap)) {
677 /* finished processing ap->tpkt */
678 clear_bit(XMIT_FULL, &ap->xmit_flags);
684 * We haven't made any progress this time around.
685 * Clear XMIT_BUSY to let other callers in, but
686 * after doing so we have to check if anyone set
687 * XMIT_WAKEUP since we last checked it. If they
688 * did, we should try again to set XMIT_BUSY and go
689 * around again in case XMIT_BUSY was still set when
690 * the other caller tried.
692 clear_bit(XMIT_BUSY, &ap->xmit_flags);
693 /* any more work to do? if not, exit the loop */
694 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
695 || (!tty_stuffed && ap->tpkt != 0)))
697 /* more work to do, see if we can do it now */
698 if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
701 spin_unlock_bh(&ap->xmit_lock);
705 clear_bit(XMIT_BUSY, &ap->xmit_flags);
709 clear_bit(XMIT_FULL, &ap->xmit_flags);
713 spin_unlock_bh(&ap->xmit_lock);
718 * Flush output from our internal buffers.
719 * Called for the TCFLSH ioctl.
722 ppp_async_flush_output(struct asyncppp *ap)
726 spin_lock_bh(&ap->xmit_lock);
728 if (ap->tpkt != NULL) {
731 clear_bit(XMIT_FULL, &ap->xmit_flags);
734 spin_unlock_bh(&ap->xmit_lock);
736 ppp_output_wakeup(&ap->chan);
740 * Receive-side routines.
743 /* see how many ordinary chars there are at the start of buf */
745 scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
749 for (i = 0; i < count; ++i) {
751 if (c == PPP_ESCAPE || c == PPP_FLAG
752 || (c < 0x20 && (ap->raccm & (1 << c)) != 0))
758 /* called when a flag is seen - do end-of-packet processing */
760 process_input_packet(struct asyncppp *ap)
764 unsigned int len, fcs, proto;
767 if (ap->state & (SC_TOSS | SC_ESCAPE))
771 return; /* 0-length packet */
777 goto err; /* too short */
779 for (; len > 0; --len)
780 fcs = PPP_FCS(fcs, *p++);
781 if (fcs != PPP_GOODFCS)
782 goto err; /* bad FCS */
783 skb_trim(skb, skb->len - 2);
785 /* check for address/control and protocol compression */
787 if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
788 /* chop off address/control */
791 p = skb_pull(skb, 2);
795 /* protocol is compressed */
796 skb_push(skb, 1)[0] = 0;
800 proto = (proto << 8) + p[1];
801 if (proto == PPP_LCP)
802 async_lcp_peek(ap, p, skb->len, 1);
805 /* queue the frame to be processed */
806 skb->cb[0] = ap->state;
807 skb_queue_tail(&ap->rqueue, skb);
813 /* frame had an error, remember that, reset SC_TOSS & SC_ESCAPE */
814 ap->state = SC_PREV_ERROR;
819 /* called when the tty driver has data for us. */
821 ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
822 char *flags, int count)
825 int c, i, j, n, s, f;
828 /* update bits used for 8-bit cleanness detection */
829 if (~ap->rbits & SC_RCV_BITS) {
831 for (i = 0; i < count; ++i) {
833 if (flags != 0 && flags[i] != 0)
835 s |= (c & 0x80)? SC_RCV_B7_1: SC_RCV_B7_0;
836 c = ((c >> 4) ^ c) & 0xf;
837 s |= (0x6996 & (1 << c))? SC_RCV_ODDP: SC_RCV_EVNP;
843 /* scan through and see how many chars we can do in bulk */
844 if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
847 n = scan_ordinary(ap, buf, count);
850 if (flags != 0 && (ap->state & SC_TOSS) == 0) {
851 /* check the flags to see if any char had an error */
852 for (j = 0; j < n; ++j)
853 if ((f = flags[j]) != 0)
858 ap->state |= SC_TOSS;
860 } else if (n > 0 && (ap->state & SC_TOSS) == 0) {
861 /* stuff the chars in the skb */
864 skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
867 /* Try to get the payload 4-byte aligned */
868 if (buf[0] != PPP_ALLSTATIONS)
869 skb_reserve(skb, 2 + (buf[0] & 1));
872 if (n > skb_tailroom(skb)) {
873 /* packet overflowed MRU */
874 ap->state |= SC_TOSS;
876 sp = skb_put(skb, n);
878 if (ap->state & SC_ESCAPE) {
880 ap->state &= ~SC_ESCAPE;
890 process_input_packet(ap);
891 } else if (c == PPP_ESCAPE) {
892 ap->state |= SC_ESCAPE;
893 } else if (I_IXON(ap->tty)) {
894 if (c == START_CHAR(ap->tty))
896 else if (c == STOP_CHAR(ap->tty))
899 /* otherwise it's a char in the recv ACCM */
910 printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
911 ap->state |= SC_TOSS;
915 * We look at LCP frames going past so that we can notice
916 * and react to the LCP configure-ack from the peer.
917 * In the situation where the peer has been sent a configure-ack
918 * already, LCP is up once it has sent its configure-ack
919 * so the immediately following packet can be sent with the
920 * configured LCP options. This allows us to process the following
921 * packet correctly without pppd needing to respond quickly.
923 * We only respond to the received configure-ack if we have just
924 * sent a configure-request, and the configure-ack contains the
925 * same data (this is checked using a 16-bit crc of the data).
927 #define CONFREQ 1 /* LCP code field values */
929 #define LCP_MRU 1 /* LCP option numbers */
930 #define LCP_ASYNCMAP 2
932 static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
933 int len, int inbound)
935 int dlen, fcs, i, code;
938 data += 2; /* skip protocol bytes */
940 if (len < 4) /* 4 = code, ID, length */
943 if (code != CONFACK && code != CONFREQ)
945 dlen = (data[2] << 8) + data[3];
947 return; /* packet got truncated or length is bogus */
949 if (code == (inbound? CONFACK: CONFREQ)) {
951 * sent confreq or received confack:
952 * calculate the crc of the data from the ID field on.
955 for (i = 1; i < dlen; ++i)
956 fcs = PPP_FCS(fcs, data[i]);
959 /* outbound confreq - remember the crc for later */
964 /* received confack, check the crc */
970 return; /* not interested in received confreq */
972 /* process the options in the confack */
975 /* data[0] is code, data[1] is length */
976 while (dlen >= 2 && dlen >= data[1]) {
979 val = (data[2] << 8) + data[3];
986 val = (data[2] << 24) + (data[3] << 16)
987 + (data[4] << 8) + data[5];
999 static void __exit ppp_async_cleanup(void)
1001 if (tty_register_ldisc(N_PPP, NULL) != 0)
1002 printk(KERN_ERR "failed to unregister PPP line discipline\n");
1005 module_init(ppp_async_init);
1006 module_exit(ppp_async_cleanup);