ppp_async.c

来自「讲述linux的初始化过程」· C语言 代码 · 共 976 行 · 第 1/2 页

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	0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
	0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
	0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
	0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};
EXPORT_SYMBOL(ppp_crc16_table);
#define fcstab	ppp_crc16_table		/* for PPP_FCS macro */

/*
 * Procedure to encode the data for async serial transmission.
 * Does octet stuffing (escaping), puts the address/control bytes
 * on if A/C compression is disabled, and does protocol compression.
 * Assumes ap->tpkt != 0 on entry.
 * Returns 1 if we finished the current frame, 0 otherwise.
 */

#define PUT_BYTE(ap, buf, c, islcp)	do {		\
	if ((islcp && c < 0x20) || (ap->xaccm[c >> 5] & (1 << (c & 0x1f)))) {\
		*buf++ = PPP_ESCAPE;			\
		*buf++ = c ^ 0x20;			\
	} else						\
		*buf++ = c;				\
} while (0)

static int
ppp_async_encode(struct asyncppp *ap)
{
	int fcs, i, count, c, proto;
	unsigned char *buf, *buflim;
	unsigned char *data;
	int islcp;

	buf = ap->obuf;
	ap->olim = buf;
	ap->optr = buf;
	i = ap->tpkt_pos;
	data = ap->tpkt->data;
	count = ap->tpkt->len;
	fcs = ap->tfcs;
	proto = (data[0] << 8) + data[1];

	/*
	 * LCP packets with code values between 1 (configure-reqest)
	 * and 7 (code-reject) must be sent as though no options
	 * had been negotiated.
	 */
	islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;

	if (i == 0) {
		if (islcp)
			async_lcp_peek(ap, data, count, 0);

		/*
		 * Start of a new packet - insert the leading FLAG
		 * character if necessary.
		 */
		if (islcp || flag_time == 0
		    || jiffies - ap->last_xmit >= flag_time)
			*buf++ = PPP_FLAG;
		ap->last_xmit = jiffies;
		fcs = PPP_INITFCS;

		/*
		 * Put in the address/control bytes if necessary
		 */
		if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
			PUT_BYTE(ap, buf, 0xff, islcp);
			fcs = PPP_FCS(fcs, 0xff);
			PUT_BYTE(ap, buf, 0x03, islcp);
			fcs = PPP_FCS(fcs, 0x03);
		}
	}

	/*
	 * Once we put in the last byte, we need to put in the FCS
	 * and closing flag, so make sure there is at least 7 bytes
	 * of free space in the output buffer.
	 */
	buflim = ap->obuf + OBUFSIZE - 6;
	while (i < count && buf < buflim) {
		c = data[i++];
		if (i == 1 && c == 0 && (ap->flags & SC_COMP_PROT))
			continue;	/* compress protocol field */
		fcs = PPP_FCS(fcs, c);
		PUT_BYTE(ap, buf, c, islcp);
	}

	if (i < count) {
		/*
		 * Remember where we are up to in this packet.
		 */
		ap->olim = buf;
		ap->tpkt_pos = i;
		ap->tfcs = fcs;
		return 0;
	}

	/*
	 * We have finished the packet.  Add the FCS and flag.
	 */
	fcs = ~fcs;
	c = fcs & 0xff;
	PUT_BYTE(ap, buf, c, islcp);
	c = (fcs >> 8) & 0xff;
	PUT_BYTE(ap, buf, c, islcp);
	*buf++ = PPP_FLAG;
	ap->olim = buf;

	kfree_skb(ap->tpkt);
	ap->tpkt = 0;
	return 1;
}

/*
 * Transmit-side routines.
 */

/*
 * Send a packet to the peer over an async 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_async_send(struct ppp_channel *chan, struct sk_buff *skb)
{
	struct asyncppp *ap = chan->private;

	ppp_async_push(ap);

	if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
		return 0;	/* already full */
	ap->tpkt = skb;
	ap->tpkt_pos = 0;

	ppp_async_push(ap);
	return 1;
}

/*
 * Push as much data as possible out to the tty.
 */
static int
ppp_async_push(struct asyncppp *ap)
{
	int avail, sent, done = 0;
	struct tty_struct *tty = ap->tty;
	int tty_stuffed = 0;

	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
	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->optr < ap->olim) {
			avail = ap->olim - ap->optr;
			set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
			sent = tty->driver.write(tty, 0, ap->optr, avail);
			if (sent < 0)
				goto flush;	/* error, e.g. loss of CD */
			ap->optr += sent;
			if (sent < avail)
				tty_stuffed = 1;
			continue;
		}
		if (ap->optr == ap->olim && ap->tpkt != 0) {
			if (ppp_async_encode(ap)) {
				/* finished processing ap->tpkt */
				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 = 0;
		clear_bit(XMIT_FULL, &ap->xmit_flags);
		done = 1;
	}
	ap->optr = ap->olim;
	spin_unlock_bh(&ap->xmit_lock);
	return done;
}

/*
 * Flush output from our internal buffers.
 * Called for the TCFLSH ioctl.
 */
static void
ppp_async_flush_output(struct asyncppp *ap)
{
	int done = 0;

	spin_lock_bh(&ap->xmit_lock);
	ap->optr = ap->olim;
	if (ap->tpkt != NULL) {
		kfree_skb(ap->tpkt);
		ap->tpkt = 0;
		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.
 */

/* see how many ordinary chars there are at the start of buf */
static inline int
scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
{
	int i, c;

	for (i = 0; i < count; ++i) {
		c = buf[i];
		if (c == PPP_ESCAPE || c == PPP_FLAG
		    || (c < 0x20 && (ap->raccm & (1 << c)) != 0))
			break;
	}
	return i;
}

/* called when a flag is seen - do end-of-packet processing */
static inline void
process_input_packet(struct asyncppp *ap)
{
	struct sk_buff *skb;
	unsigned char *p;
	unsigned int len, fcs, proto;
	int code = 0;

	skb = ap->rpkt;
	ap->rpkt = 0;
	if ((ap->state & (SC_TOSS | SC_ESCAPE)) || skb == 0) {
		ap->state &= ~(SC_TOSS | SC_ESCAPE);
		if (skb != 0)
			kfree_skb(skb);
		return;
	}

	/* check the FCS */
	p = skb->data;
	len = skb->len;
	if (len < 3)
		goto err;	/* too short */
	fcs = PPP_INITFCS;
	for (; len > 0; --len)
		fcs = PPP_FCS(fcs, *p++);
	if (fcs != PPP_GOODFCS)
		goto err;	/* bad FCS */
	skb_trim(skb, skb->len - 2);

	/* check for address/control and protocol compression */
	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);
	}
	proto = p[0];
	if (proto & 1) {
		/* protocol is compressed */
		skb_push(skb, 1)[0] = 0;
	} else {
		if (skb->len < 2)
			goto err;
		proto = (proto << 8) + p[1];
		if (proto == PPP_LCP)
			async_lcp_peek(ap, p, skb->len, 1);
	}

	/* all OK, give it to the generic layer */
	ppp_input(&ap->chan, skb);
	return;

 err:
	kfree_skb(skb);
	ppp_input_error(&ap->chan, code);
}

static inline void
input_error(struct asyncppp *ap, int code)
{
	ap->state |= SC_TOSS;
	ppp_input_error(&ap->chan, code);
}

/* called when the tty driver has data for us. */
static void
ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
		char *flags, int count)
{
	struct sk_buff *skb;
	int c, i, j, n, s, f;
	unsigned char *sp;

	/* update bits used for 8-bit cleanness detection */
	if (~ap->rbits & SC_RCV_BITS) {
		s = 0;
		for (i = 0; i < count; ++i) {
			c = buf[i];
			if (flags != 0 && flags[i] != 0)
				continue;
			s |= (c & 0x80)? SC_RCV_B7_1: SC_RCV_B7_0;
			c = ((c >> 4) ^ c) & 0xf;
			s |= (0x6996 & (1 << c))? SC_RCV_ODDP: SC_RCV_EVNP;
		}
		ap->rbits |= s;
	}

	while (count > 0) {
		/* scan through and see how many chars we can do in bulk */
		if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
			n = 1;
		else
			n = scan_ordinary(ap, buf, count);

		f = 0;
		if (flags != 0 && (ap->state & SC_TOSS) == 0) {
			/* check the flags to see if any char had an error */
			for (j = 0; j < n; ++j)
				if ((f = flags[j]) != 0)
					break;
		}
		if (f != 0) {
			/* start tossing */
			input_error(ap, f);

		} else if (n > 0 && (ap->state & SC_TOSS) == 0) {
			/* stuff the chars in the skb */
			skb = ap->rpkt;
			if (skb == 0) {
				skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
				if (skb == 0)
					goto nomem;
				/* Try to get the payload 4-byte aligned */
				if (buf[0] != PPP_ALLSTATIONS)
					skb_reserve(skb, 2 + (buf[0] & 1));
				ap->rpkt = skb;
			}
			if (n > skb_tailroom(skb)) {
				/* packet overflowed MRU */
				input_error(ap, 1);
			} else {
				sp = skb_put(skb, n);
				memcpy(sp, buf, n);
				if (ap->state & SC_ESCAPE) {
					sp[0] ^= 0x20;
					ap->state &= ~SC_ESCAPE;
				}
			}
		}

		if (n >= count)
			break;

		c = buf[n];
		if (c == PPP_FLAG) {
			process_input_packet(ap);
		} else if (c == PPP_ESCAPE) {
			ap->state |= SC_ESCAPE;
		}
		/* otherwise it's a char in the recv ACCM */
		++n;

		buf += n;
		if (flags != 0)
			flags += n;
		count -= n;
	}
	return;

 nomem:
	printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
	input_error(ap, 0);
}

/*
 * We look at LCP frames going past so that we can notice
 * and react to the LCP configure-ack from the peer.
 * In the situation where the peer has been sent a configure-ack
 * already, LCP is up once it has sent its configure-ack
 * so the immediately following packet can be sent with the
 * configured LCP options.  This allows us to process the following
 * packet correctly without pppd needing to respond quickly.
 *
 * We only respond to the received configure-ack if we have just
 * sent a configure-request, and the configure-ack contains the
 * same data (this is checked using a 16-bit crc of the data).
 */
#define CONFREQ		1	/* LCP code field values */
#define CONFACK		2
#define LCP_MRU		1	/* LCP option numbers */
#define LCP_ASYNCMAP	2

static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
			   int len, int inbound)
{
	int dlen, fcs, i, code;
	u32 val;

	data += 2;		/* skip protocol bytes */
	len -= 2;
	if (len < 4)		/* 4 = code, ID, length */
		return;
	code = data[0];
	if (code != CONFACK && code != CONFREQ)
		return;
	dlen = (data[2] << 8) + data[3];
	if (len < dlen)
		return;		/* packet got truncated or length is bogus */

	if (code == (inbound? CONFACK: CONFREQ)) {
		/*
		 * sent confreq or received confack:
		 * calculate the crc of the data from the ID field on.
		 */
		fcs = PPP_INITFCS;
		for (i = 1; i < dlen; ++i)
			fcs = PPP_FCS(fcs, data[i]);

		if (!inbound) {
			/* outbound confreq - remember the crc for later */
			ap->lcp_fcs = fcs;
			return;
		}

		/* received confack, check the crc */
		fcs ^= ap->lcp_fcs;
		ap->lcp_fcs = -1;
		if (fcs != 0)
			return;
	} else if (inbound)
		return;	/* not interested in received confreq */

	/* process the options in the confack */
	data += 4;
	dlen -= 4;
	/* data[0] is code, data[1] is length */
	while (dlen >= 2 && dlen >= data[1]) {
		switch (data[0]) {
		case LCP_MRU:
			val = (data[2] << 8) + data[3];
			if (inbound)
				ap->mru = val;
			else
				ap->chan.mtu = val;
			break;
		case LCP_ASYNCMAP:
			val = (data[2] << 24) + (data[3] << 16)
				+ (data[4] << 8) + data[5];
			if (inbound)
				ap->raccm = val;
			else
				ap->xaccm[0] = val;
			break;
		}
		dlen -= data[1];
		data += data[1];
	}
}

void __exit ppp_async_cleanup(void)
{
	if (tty_register_ldisc(N_PPP, NULL) != 0)
		printk(KERN_ERR "failed to unregister PPP line discipline\n");
}

module_init(ppp_async_init);
module_exit(ppp_async_cleanup);