Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

5 files changed, 2389 insertions, 0 deletions

diff --git a/drivers/net/slip/Kconfig b/drivers/net/slip/Kconfig
new file mode 100644
index 000000000..ea68fc15c
--- /dev/null
+++ b/drivers/net/slip/Kconfig
@@ -0,0 +1,81 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# SLIP network device configuration
+#
+
+config SLIP
+	tristate "SLIP (serial line) support"
+	depends on TTY
+	help
+	  Say Y if you intend to use SLIP or CSLIP (compressed SLIP) to
+	  connect to your Internet service provider or to connect to some
+	  other local Unix box or if you want to configure your Linux box as a
+	  Slip/CSlip server for other people to dial in. SLIP (Serial Line
+	  Internet Protocol) is a protocol used to send Internet traffic over
+	  serial connections such as telephone lines or null modem cables;
+	  nowadays, the protocol PPP is more commonly used for this same
+	  purpose.
+
+	  Normally, your access provider has to support SLIP in order for you
+	  to be able to use it, but there is now a SLIP emulator called SLiRP
+	  around (available from
+	  <ftp://ibiblio.org/pub/Linux/system/network/serial/>) which
+	  allows you to use SLIP over a regular dial up shell connection. If
+	  you plan to use SLiRP, make sure to say Y to CSLIP, below. The
+	  NET-3-HOWTO, available from
+	  <http://www.tldp.org/docs.html#howto>, explains how to
+	  configure SLIP. Note that you don't need this option if you just
+	  want to run term (term is a program which gives you almost full
+	  Internet connectivity if you have a regular dial up shell account on
+	  some Internet connected Unix computer. Read
+	  <http://www.bart.nl/~patrickr/term-howto/Term-HOWTO.html>). SLIP
+	  support will enlarge your kernel by about 4 KB. If unsure, say N.
+
+	  To compile this driver as a module, choose M here. The module
+	  will be called slip.
+
+config SLHC
+	tristate
+	help
+	  This option enables Van Jacobsen serial line header compression
+	  routines.
+
+if SLIP
+
+config SLIP_COMPRESSED
+	bool "CSLIP compressed headers"
+	depends on SLIP
+	select SLHC
+	help
+	  This protocol is faster than SLIP because it uses compression on the
+	  TCP/IP headers (not on the data itself), but it has to be supported
+	  on both ends. Ask your access provider if you are not sure and
+	  answer Y, just in case. You will still be able to use plain SLIP. If
+	  you plan to use SLiRP, the SLIP emulator (available from
+	  <ftp://ibiblio.org/pub/Linux/system/network/serial/>) which
+	  allows you to use SLIP over a regular dial up shell connection, you
+	  definitely want to say Y here. The NET-3-HOWTO, available from
+	  <http://www.tldp.org/docs.html#howto>, explains how to configure
+	  CSLIP. This won't enlarge your kernel.
+
+config SLIP_SMART
+	bool "Keepalive and linefill"
+	depends on SLIP
+	help
+	  Adds additional capabilities to the SLIP driver to support the
+	  RELCOM line fill and keepalive monitoring. Ideal on poor quality
+	  analogue lines.
+
+config SLIP_MODE_SLIP6
+	bool "Six bit SLIP encapsulation"
+	depends on SLIP
+	help
+	  Just occasionally you may need to run IP over hostile serial
+	  networks that don't pass all control characters or are only seven
+	  bit. Saying Y here adds an extra mode you can use with SLIP:
+	  "slip6". In this mode, SLIP will only send normal ASCII symbols over
+	  the serial device. Naturally, this has to be supported at the other
+	  end of the link as well. It's good enough, for example, to run IP
+	  over the async ports of a Camtec JNT Pad. If unsure, say N.
+
+endif # SLIP
diff --git a/drivers/net/slip/Makefile b/drivers/net/slip/Makefile
new file mode 100644
index 000000000..668c1afb3
--- /dev/null
+++ b/drivers/net/slip/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for the SLIP network device drivers.
+#
+
+obj-$(CONFIG_SLIP) += slip.o
+obj-$(CONFIG_SLHC) += slhc.o
diff --git a/drivers/net/slip/slhc.c b/drivers/net/slip/slhc.c
new file mode 100644
index 000000000..ba93bab94
--- /dev/null
+++ b/drivers/net/slip/slhc.c
@@ -0,0 +1,755 @@
+/*
+ * Routines to compress and uncompress tcp packets (for transmission
+ * over low speed serial lines).
+ *
+ * Copyright (c) 1989 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted
+ * provided that the above copyright notice and this paragraph are
+ * duplicated in all such forms and that any documentation,
+ * advertising materials, and other materials related to such
+ * distribution and use acknowledge that the software was developed
+ * by the University of California, Berkeley.  The name of the
+ * University may not be used to endorse or promote products derived
+ * from this software without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
+ *	- Initial distribution.
+ *
+ *
+ * modified for KA9Q Internet Software Package by
+ * Katie Stevens (dkstevens@ucdavis.edu)
+ * University of California, Davis
+ * Computing Services
+ *	- 01-31-90	initial adaptation (from 1.19)
+ *	PPP.05	02-15-90 [ks]
+ *	PPP.08	05-02-90 [ks]	use PPP protocol field to signal compression
+ *	PPP.15	09-90	 [ks]	improve mbuf handling
+ *	PPP.16	11-02	 [karn]	substantially rewritten to use NOS facilities
+ *
+ *	- Feb 1991	Bill_Simpson@um.cc.umich.edu
+ *			variable number of conversation slots
+ *			allow zero or one slots
+ *			separate routines
+ *			status display
+ *	- Jul 1994	Dmitry Gorodchanin
+ *			Fixes for memory leaks.
+ *      - Oct 1994      Dmitry Gorodchanin
+ *                      Modularization.
+ *	- Jan 1995	Bjorn Ekwall
+ *			Use ip_fast_csum from ip.h
+ *	- July 1995	Christos A. Polyzols
+ *			Spotted bug in tcp option checking
+ *
+ *
+ *	This module is a difficult issue. It's clearly inet code but it's also clearly
+ *	driver code belonging close to PPP and SLIP
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <net/slhc_vj.h>
+
+#ifdef CONFIG_INET
+/* Entire module is for IP only */
+#include <linux/mm.h>
+#include <linux/socket.h>
+#include <linux/sockios.h>
+#include <linux/termios.h>
+#include <linux/in.h>
+#include <linux/fcntl.h>
+#include <linux/inet.h>
+#include <linux/netdevice.h>
+#include <net/ip.h>
+#include <net/protocol.h>
+#include <net/icmp.h>
+#include <net/tcp.h>
+#include <linux/skbuff.h>
+#include <net/sock.h>
+#include <linux/timer.h>
+#include <linux/uaccess.h>
+#include <net/checksum.h>
+#include <asm/unaligned.h>
+
+static unsigned char *encode(unsigned char *cp, unsigned short n);
+static long decode(unsigned char **cpp);
+static unsigned char * put16(unsigned char *cp, unsigned short x);
+static unsigned short pull16(unsigned char **cpp);
+
+/* Allocate compression data structure
+ *	slots must be in range 0 to 255 (zero meaning no compression)
+ * Returns pointer to structure or ERR_PTR() on error.
+ */
+struct slcompress *
+slhc_init(int rslots, int tslots)
+{
+	short i;
+	struct cstate *ts;
+	struct slcompress *comp;
+
+	if (rslots < 0 || rslots > 255 || tslots < 0 || tslots > 255)
+		return ERR_PTR(-EINVAL);
+
+	comp = kzalloc(sizeof(struct slcompress), GFP_KERNEL);
+	if (! comp)
+		goto out_fail;
+
+	if (rslots > 0) {
+		size_t rsize = rslots * sizeof(struct cstate);
+		comp->rstate = kzalloc(rsize, GFP_KERNEL);
+		if (! comp->rstate)
+			goto out_free;
+		comp->rslot_limit = rslots - 1;
+	}
+
+	if (tslots > 0) {
+		size_t tsize = tslots * sizeof(struct cstate);
+		comp->tstate = kzalloc(tsize, GFP_KERNEL);
+		if (! comp->tstate)
+			goto out_free2;
+		comp->tslot_limit = tslots - 1;
+	}
+
+	comp->xmit_oldest = 0;
+	comp->xmit_current = 255;
+	comp->recv_current = 255;
+	/*
+	 * don't accept any packets with implicit index until we get
+	 * one with an explicit index.  Otherwise the uncompress code
+	 * will try to use connection 255, which is almost certainly
+	 * out of range
+	 */
+	comp->flags |= SLF_TOSS;
+
+	if ( tslots > 0 ) {
+		ts = comp->tstate;
+		for(i = comp->tslot_limit; i > 0; --i){
+			ts[i].cs_this = i;
+			ts[i].next = &(ts[i - 1]);
+		}
+		ts[0].next = &(ts[comp->tslot_limit]);
+		ts[0].cs_this = 0;
+	}
+	return comp;
+
+out_free2:
+	kfree(comp->rstate);
+out_free:
+	kfree(comp);
+out_fail:
+	return ERR_PTR(-ENOMEM);
+}
+
+
+/* Free a compression data structure */
+void
+slhc_free(struct slcompress *comp)
+{
+	if ( IS_ERR_OR_NULL(comp) )
+		return;
+
+	if ( comp->tstate != NULLSLSTATE )
+		kfree( comp->tstate );
+
+	if ( comp->rstate != NULLSLSTATE )
+		kfree( comp->rstate );
+
+	kfree( comp );
+}
+
+
+/* Put a short in host order into a char array in network order */
+static inline unsigned char *
+put16(unsigned char *cp, unsigned short x)
+{
+	*cp++ = x >> 8;
+	*cp++ = x;
+
+	return cp;
+}
+
+
+/* Encode a number */
+static unsigned char *
+encode(unsigned char *cp, unsigned short n)
+{
+	if(n >= 256 || n == 0){
+		*cp++ = 0;
+		cp = put16(cp,n);
+	} else {
+		*cp++ = n;
+	}
+	return cp;
+}
+
+/* Pull a 16-bit integer in host order from buffer in network byte order */
+static unsigned short
+pull16(unsigned char **cpp)
+{
+	short rval;
+
+	rval = *(*cpp)++;
+	rval <<= 8;
+	rval |= *(*cpp)++;
+	return rval;
+}
+
+/* Decode a number */
+static long
+decode(unsigned char **cpp)
+{
+	int x;
+
+	x = *(*cpp)++;
+	if(x == 0){
+		return pull16(cpp) & 0xffff;	/* pull16 returns -1 on error */
+	} else {
+		return x & 0xff;		/* -1 if PULLCHAR returned error */
+	}
+}
+
+/*
+ * icp and isize are the original packet.
+ * ocp is a place to put a copy if necessary.
+ * cpp is initially a pointer to icp.  If the copy is used,
+ *    change it to ocp.
+ */
+
+int
+slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
+	unsigned char *ocp, unsigned char **cpp, int compress_cid)
+{
+	struct cstate *ocs = &(comp->tstate[comp->xmit_oldest]);
+	struct cstate *lcs = ocs;
+	struct cstate *cs = lcs->next;
+	unsigned long deltaS, deltaA;
+	short changes = 0;
+	int nlen, hlen;
+	unsigned char new_seq[16];
+	unsigned char *cp = new_seq;
+	struct iphdr *ip;
+	struct tcphdr *th, *oth;
+	__sum16 csum;
+
+
+	/*
+	 *	Don't play with runt packets.
+	 */
+
+	if(isize<sizeof(struct iphdr))
+		return isize;
+
+	ip = (struct iphdr *) icp;
+	if (ip->version != 4 || ip->ihl < 5)
+		return isize;
+
+	/* Bail if this packet isn't TCP, or is an IP fragment */
+	if (ip->protocol != IPPROTO_TCP || (ntohs(ip->frag_off) & 0x3fff)) {
+		/* Send as regular IP */
+		if(ip->protocol != IPPROTO_TCP)
+			comp->sls_o_nontcp++;
+		else
+			comp->sls_o_tcp++;
+		return isize;
+	}
+	nlen = ip->ihl * 4;
+	if (isize < nlen + sizeof(*th))
+		return isize;
+
+	th = (struct tcphdr *)(icp + nlen);
+	if (th->doff < sizeof(struct tcphdr) / 4)
+		return isize;
+	hlen = nlen + th->doff * 4;
+
+	/*  Bail if the TCP packet isn't `compressible' (i.e., ACK isn't set or
+	 *  some other control bit is set). Also uncompressible if
+	 *  it's a runt.
+	 */
+	if(hlen > isize || th->syn || th->fin || th->rst ||
+	    ! (th->ack)){
+		/* TCP connection stuff; send as regular IP */
+		comp->sls_o_tcp++;
+		return isize;
+	}
+	/*
+	 * Packet is compressible -- we're going to send either a
+	 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way,
+	 * we need to locate (or create) the connection state.
+	 *
+	 * States are kept in a circularly linked list with
+	 * xmit_oldest pointing to the end of the list.  The
+	 * list is kept in lru order by moving a state to the
+	 * head of the list whenever it is referenced.  Since
+	 * the list is short and, empirically, the connection
+	 * we want is almost always near the front, we locate
+	 * states via linear search.  If we don't find a state
+	 * for the datagram, the oldest state is (re-)used.
+	 */
+	for ( ; ; ) {
+		if( ip->saddr == cs->cs_ip.saddr
+		 && ip->daddr == cs->cs_ip.daddr
+		 && th->source == cs->cs_tcp.source
+		 && th->dest == cs->cs_tcp.dest)
+			goto found;
+
+		/* if current equal oldest, at end of list */
+		if ( cs == ocs )
+			break;
+		lcs = cs;
+		cs = cs->next;
+		comp->sls_o_searches++;
+	}
+	/*
+	 * Didn't find it -- re-use oldest cstate.  Send an
+	 * uncompressed packet that tells the other side what
+	 * connection number we're using for this conversation.
+	 *
+	 * Note that since the state list is circular, the oldest
+	 * state points to the newest and we only need to set
+	 * xmit_oldest to update the lru linkage.
+	 */
+	comp->sls_o_misses++;
+	comp->xmit_oldest = lcs->cs_this;
+	goto uncompressed;
+
+found:
+	/*
+	 * Found it -- move to the front on the connection list.
+	 */
+	if(lcs == ocs) {
+		/* found at most recently used */
+	} else if (cs == ocs) {
+		/* found at least recently used */
+		comp->xmit_oldest = lcs->cs_this;
+	} else {
+		/* more than 2 elements */
+		lcs->next = cs->next;
+		cs->next = ocs->next;
+		ocs->next = cs;
+	}
+
+	/*
+	 * Make sure that only what we expect to change changed.
+	 * Check the following:
+	 * IP protocol version, header length & type of service.
+	 * The "Don't fragment" bit.
+	 * The time-to-live field.
+	 * The TCP header length.
+	 * IP options, if any.
+	 * TCP options, if any.
+	 * If any of these things are different between the previous &
+	 * current datagram, we send the current datagram `uncompressed'.
+	 */
+	oth = &cs->cs_tcp;
+
+	if(ip->version != cs->cs_ip.version || ip->ihl != cs->cs_ip.ihl
+	 || ip->tos != cs->cs_ip.tos
+	 || (ip->frag_off & htons(0x4000)) != (cs->cs_ip.frag_off & htons(0x4000))
+	 || ip->ttl != cs->cs_ip.ttl
+	 || th->doff != cs->cs_tcp.doff
+	 || (ip->ihl > 5 && memcmp(ip+1,cs->cs_ipopt,((ip->ihl)-5)*4) != 0)
+	 || (th->doff > 5 && memcmp(th+1,cs->cs_tcpopt,((th->doff)-5)*4) != 0)){
+		goto uncompressed;
+	}
+
+	/*
+	 * Figure out which of the changing fields changed.  The
+	 * receiver expects changes in the order: urgent, window,
+	 * ack, seq (the order minimizes the number of temporaries
+	 * needed in this section of code).
+	 */
+	if(th->urg){
+		deltaS = ntohs(th->urg_ptr);
+		cp = encode(cp,deltaS);
+		changes |= NEW_U;
+	} else if(th->urg_ptr != oth->urg_ptr){
+		/* argh! URG not set but urp changed -- a sensible
+		 * implementation should never do this but RFC793
+		 * doesn't prohibit the change so we have to deal
+		 * with it. */
+		goto uncompressed;
+	}
+	if((deltaS = ntohs(th->window) - ntohs(oth->window)) != 0){
+		cp = encode(cp,deltaS);
+		changes |= NEW_W;
+	}
+	if((deltaA = ntohl(th->ack_seq) - ntohl(oth->ack_seq)) != 0L){
+		if(deltaA > 0x0000ffff)
+			goto uncompressed;
+		cp = encode(cp,deltaA);
+		changes |= NEW_A;
+	}
+	if((deltaS = ntohl(th->seq) - ntohl(oth->seq)) != 0L){
+		if(deltaS > 0x0000ffff)
+			goto uncompressed;
+		cp = encode(cp,deltaS);
+		changes |= NEW_S;
+	}
+
+	switch(changes){
+	case 0:	/* Nothing changed. If this packet contains data and the
+		 * last one didn't, this is probably a data packet following
+		 * an ack (normal on an interactive connection) and we send
+		 * it compressed.  Otherwise it's probably a retransmit,
+		 * retransmitted ack or window probe.  Send it uncompressed
+		 * in case the other side missed the compressed version.
+		 */
+		if(ip->tot_len != cs->cs_ip.tot_len &&
+		   ntohs(cs->cs_ip.tot_len) == hlen)
+			break;
+		goto uncompressed;
+	case SPECIAL_I:
+	case SPECIAL_D:
+		/* actual changes match one of our special case encodings --
+		 * send packet uncompressed.
+		 */
+		goto uncompressed;
+	case NEW_S|NEW_A:
+		if(deltaS == deltaA &&
+		    deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
+			/* special case for echoed terminal traffic */
+			changes = SPECIAL_I;
+			cp = new_seq;
+		}
+		break;
+	case NEW_S:
+		if(deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
+			/* special case for data xfer */
+			changes = SPECIAL_D;
+			cp = new_seq;
+		}
+		break;
+	}
+	deltaS = ntohs(ip->id) - ntohs(cs->cs_ip.id);
+	if(deltaS != 1){
+		cp = encode(cp,deltaS);
+		changes |= NEW_I;
+	}
+	if(th->psh)
+		changes |= TCP_PUSH_BIT;
+	/* Grab the cksum before we overwrite it below.  Then update our
+	 * state with this packet's header.
+	 */
+	csum = th->check;
+	memcpy(&cs->cs_ip,ip,20);
+	memcpy(&cs->cs_tcp,th,20);
+	/* We want to use the original packet as our compressed packet.
+	 * (cp - new_seq) is the number of bytes we need for compressed
+	 * sequence numbers.  In addition we need one byte for the change
+	 * mask, one for the connection id and two for the tcp checksum.
+	 * So, (cp - new_seq) + 4 bytes of header are needed.
+	 */
+	deltaS = cp - new_seq;
+	if(compress_cid == 0 || comp->xmit_current != cs->cs_this){
+		cp = ocp;
+		*cpp = ocp;
+		*cp++ = changes | NEW_C;
+		*cp++ = cs->cs_this;
+		comp->xmit_current = cs->cs_this;
+	} else {
+		cp = ocp;
+		*cpp = ocp;
+		*cp++ = changes;
+	}
+	*(__sum16 *)cp = csum;
+	cp += 2;
+/* deltaS is now the size of the change section of the compressed header */
+	memcpy(cp,new_seq,deltaS);	/* Write list of deltas */
+	memcpy(cp+deltaS,icp+hlen,isize-hlen);
+	comp->sls_o_compressed++;
+	ocp[0] |= SL_TYPE_COMPRESSED_TCP;
+	return isize - hlen + deltaS + (cp - ocp);
+
+	/* Update connection state cs & send uncompressed packet (i.e.,
+	 * a regular ip/tcp packet but with the 'conversation id' we hope
+	 * to use on future compressed packets in the protocol field).
+	 */
+uncompressed:
+	memcpy(&cs->cs_ip,ip,20);
+	memcpy(&cs->cs_tcp,th,20);
+	if (ip->ihl > 5)
+	  memcpy(cs->cs_ipopt, ip+1, ((ip->ihl) - 5) * 4);
+	if (th->doff > 5)
+	  memcpy(cs->cs_tcpopt, th+1, ((th->doff) - 5) * 4);
+	comp->xmit_current = cs->cs_this;
+	comp->sls_o_uncompressed++;
+	memcpy(ocp, icp, isize);
+	*cpp = ocp;
+	ocp[9] = cs->cs_this;
+	ocp[0] |= SL_TYPE_UNCOMPRESSED_TCP;
+	return isize;
+}
+
+
+int
+slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
+{
+	int changes;
+	long x;
+	struct tcphdr *thp;
+	struct iphdr *ip;
+	struct cstate *cs;
+	int len, hdrlen;
+	unsigned char *cp = icp;
+
+	/* We've got a compressed packet; read the change byte */
+	comp->sls_i_compressed++;
+	if(isize < 3){
+		comp->sls_i_error++;
+		return 0;
+	}
+	changes = *cp++;
+	if(changes & NEW_C){
+		/* Make sure the state index is in range, then grab the state.
+		 * If we have a good state index, clear the 'discard' flag.
+		 */
+		x = *cp++;	/* Read conn index */
+		if(x < 0 || x > comp->rslot_limit)
+			goto bad;
+
+		/* Check if the cstate is initialized */
+		if (!comp->rstate[x].initialized)
+			goto bad;
+
+		comp->flags &=~ SLF_TOSS;
+		comp->recv_current = x;
+	} else {
+		/* this packet has an implicit state index.  If we've
+		 * had a line error since the last time we got an
+		 * explicit state index, we have to toss the packet. */
+		if(comp->flags & SLF_TOSS){
+			comp->sls_i_tossed++;
+			return 0;
+		}
+	}
+	cs = &comp->rstate[comp->recv_current];
+	thp = &cs->cs_tcp;
+	ip = &cs->cs_ip;
+
+	thp->check = *(__sum16 *)cp;
+	cp += 2;
+
+	thp->psh = (changes & TCP_PUSH_BIT) ? 1 : 0;
+/*
+ * we can use the same number for the length of the saved header and
+ * the current one, because the packet wouldn't have been sent
+ * as compressed unless the options were the same as the previous one
+ */
+
+	hdrlen = ip->ihl * 4 + thp->doff * 4;
+
+	switch(changes & SPECIALS_MASK){
+	case SPECIAL_I:		/* Echoed terminal traffic */
+		{
+		short i;
+		i = ntohs(ip->tot_len) - hdrlen;
+		thp->ack_seq = htonl( ntohl(thp->ack_seq) + i);
+		thp->seq = htonl( ntohl(thp->seq) + i);
+		}
+		break;
+
+	case SPECIAL_D:			/* Unidirectional data */
+		thp->seq = htonl( ntohl(thp->seq) +
+				  ntohs(ip->tot_len) - hdrlen);
+		break;
+
+	default:
+		if(changes & NEW_U){
+			thp->urg = 1;
+			if((x = decode(&cp)) == -1) {
+				goto bad;
+			}
+			thp->urg_ptr = htons(x);
+		} else
+			thp->urg = 0;
+		if(changes & NEW_W){
+			if((x = decode(&cp)) == -1) {
+				goto bad;
+			}
+			thp->window = htons( ntohs(thp->window) + x);
+		}
+		if(changes & NEW_A){
+			if((x = decode(&cp)) == -1) {
+				goto bad;
+			}
+			thp->ack_seq = htonl( ntohl(thp->ack_seq) + x);
+		}
+		if(changes & NEW_S){
+			if((x = decode(&cp)) == -1) {
+				goto bad;
+			}
+			thp->seq = htonl( ntohl(thp->seq) + x);
+		}
+		break;
+	}
+	if(changes & NEW_I){
+		if((x = decode(&cp)) == -1) {
+			goto bad;
+		}
+		ip->id = htons (ntohs (ip->id) + x);
+	} else
+		ip->id = htons (ntohs (ip->id) + 1);
+
+	/*
+	 * At this point, cp points to the first byte of data in the
+	 * packet.  Put the reconstructed TCP and IP headers back on the
+	 * packet.  Recalculate IP checksum (but not TCP checksum).
+	 */
+
+	len = isize - (cp - icp);
+	if (len < 0)
+		goto bad;
+	len += hdrlen;
+	ip->tot_len = htons(len);
+	ip->check = 0;
+
+	memmove(icp + hdrlen, cp, len - hdrlen);
+
+	cp = icp;
+	memcpy(cp, ip, 20);
+	cp += 20;
+
+	if (ip->ihl > 5) {
+	  memcpy(cp, cs->cs_ipopt, (ip->ihl - 5) * 4);
+	  cp += (ip->ihl - 5) * 4;
+	}
+
+	put_unaligned(ip_fast_csum(icp, ip->ihl),
+		      &((struct iphdr *)icp)->check);
+
+	memcpy(cp, thp, 20);
+	cp += 20;
+
+	if (thp->doff > 5) {
+	  memcpy(cp, cs->cs_tcpopt, ((thp->doff) - 5) * 4);
+	  cp += ((thp->doff) - 5) * 4;
+	}
+
+	return len;
+bad:
+	comp->sls_i_error++;
+	return slhc_toss( comp );
+}
+
+
+int
+slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
+{
+	struct cstate *cs;
+	unsigned ihl;
+
+	unsigned char index;
+
+	if(isize < 20) {
+		/* The packet is shorter than a legal IP header */
+		comp->sls_i_runt++;
+		return slhc_toss( comp );
+	}
+	/* Peek at the IP header's IHL field to find its length */
+	ihl = icp[0] & 0xf;
+	if(ihl < 20 / 4){
+		/* The IP header length field is too small */
+		comp->sls_i_runt++;
+		return slhc_toss( comp );
+	}
+	index = icp[9];
+	icp[9] = IPPROTO_TCP;
+
+	if (ip_fast_csum(icp, ihl)) {
+		/* Bad IP header checksum; discard */
+		comp->sls_i_badcheck++;
+		return slhc_toss( comp );
+	}
+	if(index > comp->rslot_limit) {
+		comp->sls_i_error++;
+		return slhc_toss(comp);
+	}
+
+	/* Update local state */
+	cs = &comp->rstate[comp->recv_current = index];
+	comp->flags &=~ SLF_TOSS;
+	memcpy(&cs->cs_ip,icp,20);
+	memcpy(&cs->cs_tcp,icp + ihl*4,20);
+	if (ihl > 5)
+	  memcpy(cs->cs_ipopt, icp + sizeof(struct iphdr), (ihl - 5) * 4);
+	if (cs->cs_tcp.doff > 5)
+	  memcpy(cs->cs_tcpopt, icp + ihl*4 + sizeof(struct tcphdr), (cs->cs_tcp.doff - 5) * 4);
+	cs->cs_hsize = ihl*2 + cs->cs_tcp.doff*2;
+	cs->initialized = true;
+	/* Put headers back on packet
+	 * Neither header checksum is recalculated
+	 */
+	comp->sls_i_uncompressed++;
+	return isize;
+}
+
+int
+slhc_toss(struct slcompress *comp)
+{
+	if ( comp == NULLSLCOMPR )
+		return 0;
+
+	comp->flags |= SLF_TOSS;
+	return 0;
+}
+
+#else /* CONFIG_INET */
+
+int
+slhc_toss(struct slcompress *comp)
+{
+  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_toss");
+  return -EINVAL;
+}
+int
+slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
+{
+  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_uncompress");
+  return -EINVAL;
+}
+int
+slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
+	unsigned char *ocp, unsigned char **cpp, int compress_cid)
+{
+  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_compress");
+  return -EINVAL;
+}
+
+int
+slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
+{
+  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_remember");
+  return -EINVAL;
+}
+
+void
+slhc_free(struct slcompress *comp)
+{
+  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_free");
+}
+struct slcompress *
+slhc_init(int rslots, int tslots)
+{
+  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_init");
+  return NULL;
+}
+
+#endif /* CONFIG_INET */
+
+/* VJ header compression */
+EXPORT_SYMBOL(slhc_init);
+EXPORT_SYMBOL(slhc_free);
+EXPORT_SYMBOL(slhc_remember);
+EXPORT_SYMBOL(slhc_compress);
+EXPORT_SYMBOL(slhc_uncompress);
+EXPORT_SYMBOL(slhc_toss);
+
+MODULE_LICENSE("Dual BSD/GPL");
diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c
new file mode 100644
index 000000000..6865d3227
--- /dev/null
+++ b/drivers/net/slip/slip.c
@@ -0,0 +1,1441 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * slip.c	This module implements the SLIP protocol for kernel-based
+ *		devices like TTY.  It interfaces between a raw TTY, and the
+ *		kernel's INET protocol layers.
+ *
+ * Version:	@(#)slip.c	0.8.3	12/24/94
+ *
+ * Authors:	Laurence Culhane, <loz@holmes.demon.co.uk>
+ *		Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
+ *
+ * Fixes:
+ *		Alan Cox	: 	Sanity checks and avoid tx overruns.
+ *					Has a new sl->mtu field.
+ *		Alan Cox	: 	Found cause of overrun. ifconfig sl0
+ *					mtu upwards. Driver now spots this
+ *					and grows/shrinks its buffers(hack!).
+ *					Memory leak if you run out of memory
+ *					setting up a slip driver fixed.
+ *		Matt Dillon	:	Printable slip (borrowed from NET2E)
+ *	Pauline Middelink	:	Slip driver fixes.
+ *		Alan Cox	:	Honours the old SL_COMPRESSED flag
+ *		Alan Cox	:	KISS AX.25 and AXUI IP support
+ *		Michael Riepe	:	Automatic CSLIP recognition added
+ *		Charles Hedrick :	CSLIP header length problem fix.
+ *		Alan Cox	:	Corrected non-IP cases of the above.
+ *		Alan Cox	:	Now uses hardware type as per FvK.
+ *		Alan Cox	:	Default to 192.168.0.0 (RFC 1597)
+ *		A.N.Kuznetsov	:	dev_tint() recursion fix.
+ *	Dmitry Gorodchanin	:	SLIP memory leaks
+ *      Dmitry Gorodchanin      :       Code cleanup. Reduce tty driver
+ *                                      buffering from 4096 to 256 bytes.
+ *                                      Improving SLIP response time.
+ *                                      CONFIG_SLIP_MODE_SLIP6.
+ *                                      ifconfig sl? up & down now works
+ *					correctly.
+ *					Modularization.
+ *              Alan Cox        :       Oops - fix AX.25 buffer lengths
+ *      Dmitry Gorodchanin      :       Even more cleanups. Preserve CSLIP
+ *                                      statistics. Include CSLIP code only
+ *                                      if it really needed.
+ *		Alan Cox	:	Free slhc buffers in the right place.
+ *		Alan Cox	:	Allow for digipeated IP over AX.25
+ *		Matti Aarnio	:	Dynamic SLIP devices, with ideas taken
+ *					from Jim Freeman's <jfree@caldera.com>
+ *					dynamic PPP devices.  We do NOT kfree()
+ *					device entries, just reg./unreg. them
+ *					as they are needed.  We kfree() them
+ *					at module cleanup.
+ *					With MODULE-loading ``insmod'', user
+ *					can issue parameter:  slip_maxdev=1024
+ *					(Or how much he/she wants.. Default
+ *					is 256)
+ *	Stanislav Voronyi	:	Slip line checking, with ideas taken
+ *					from multislip BSDI driver which was
+ *					written by Igor Chechik, RELCOM Corp.
+ *					Only algorithms have been ported to
+ *					Linux SLIP driver.
+ *	Vitaly E. Lavrov	:	Sane behaviour on tty hangup.
+ *	Alexey Kuznetsov	:	Cleanup interfaces to tty & netdevice
+ *					modules.
+ */
+
+#define SL_CHECK_TRANSMIT
+#include <linux/compat.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+
+#include <linux/uaccess.h>
+#include <linux/bitops.h>
+#include <linux/sched/signal.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/interrupt.h>
+#include <linux/in.h>
+#include <linux/tty.h>
+#include <linux/errno.h>
+#include <linux/netdevice.h>
+#include <linux/etherdevice.h>
+#include <linux/skbuff.h>
+#include <linux/rtnetlink.h>
+#include <linux/if_arp.h>
+#include <linux/if_slip.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+#include "slip.h"
+#ifdef CONFIG_INET
+#include <linux/ip.h>
+#include <linux/tcp.h>
+#include <net/slhc_vj.h>
+#endif
+
+#define SLIP_VERSION	"0.8.4-NET3.019-NEWTTY"
+
+static struct net_device **slip_devs;
+
+static int slip_maxdev = SL_NRUNIT;
+module_param(slip_maxdev, int, 0);
+MODULE_PARM_DESC(slip_maxdev, "Maximum number of slip devices");
+
+static int slip_esc(unsigned char *p, unsigned char *d, int len);
+static void slip_unesc(struct slip *sl, unsigned char c);
+#ifdef CONFIG_SLIP_MODE_SLIP6
+static int slip_esc6(unsigned char *p, unsigned char *d, int len);
+static void slip_unesc6(struct slip *sl, unsigned char c);
+#endif
+#ifdef CONFIG_SLIP_SMART
+static void sl_keepalive(struct timer_list *t);
+static void sl_outfill(struct timer_list *t);
+static int sl_siocdevprivate(struct net_device *dev, struct ifreq *rq, void __user *data, int cmd);
+#endif
+
+/********************************
+*  Buffer administration routines:
+*	sl_alloc_bufs()
+*	sl_free_bufs()
+*	sl_realloc_bufs()
+*
+* NOTE: sl_realloc_bufs != sl_free_bufs + sl_alloc_bufs, because
+*	sl_realloc_bufs provides strong atomicity and reallocation
+*	on actively running device.
+*********************************/
+
+/*
+   Allocate channel buffers.
+ */
+
+static int sl_alloc_bufs(struct slip *sl, int mtu)
+{
+	int err = -ENOBUFS;
+	unsigned long len;
+	char *rbuff = NULL;
+	char *xbuff = NULL;
+#ifdef SL_INCLUDE_CSLIP
+	char *cbuff = NULL;
+	struct slcompress *slcomp = NULL;
+#endif
+
+	/*
+	 * Allocate the SLIP frame buffers:
+	 *
+	 * rbuff	Receive buffer.
+	 * xbuff	Transmit buffer.
+	 * cbuff        Temporary compression buffer.
+	 */
+	len = mtu * 2;
+
+	/*
+	 * allow for arrival of larger UDP packets, even if we say not to
+	 * also fixes a bug in which SunOS sends 512-byte packets even with
+	 * an MSS of 128
+	 */
+	if (len < 576 * 2)
+		len = 576 * 2;
+	rbuff = kmalloc(len + 4, GFP_KERNEL);
+	if (rbuff == NULL)
+		goto err_exit;
+	xbuff = kmalloc(len + 4, GFP_KERNEL);
+	if (xbuff == NULL)
+		goto err_exit;
+#ifdef SL_INCLUDE_CSLIP
+	cbuff = kmalloc(len + 4, GFP_KERNEL);
+	if (cbuff == NULL)
+		goto err_exit;
+	slcomp = slhc_init(16, 16);
+	if (IS_ERR(slcomp))
+		goto err_exit;
+#endif
+	spin_lock_bh(&sl->lock);
+	if (sl->tty == NULL) {
+		spin_unlock_bh(&sl->lock);
+		err = -ENODEV;
+		goto err_exit;
+	}
+	sl->mtu	     = mtu;
+	sl->buffsize = len;
+	sl->rcount   = 0;
+	sl->xleft    = 0;
+	rbuff = xchg(&sl->rbuff, rbuff);
+	xbuff = xchg(&sl->xbuff, xbuff);
+#ifdef SL_INCLUDE_CSLIP
+	cbuff = xchg(&sl->cbuff, cbuff);
+	slcomp = xchg(&sl->slcomp, slcomp);
+#endif
+#ifdef CONFIG_SLIP_MODE_SLIP6
+	sl->xdata    = 0;
+	sl->xbits    = 0;
+#endif
+	spin_unlock_bh(&sl->lock);
+	err = 0;
+
+	/* Cleanup */
+err_exit:
+#ifdef SL_INCLUDE_CSLIP
+	kfree(cbuff);
+	slhc_free(slcomp);
+#endif
+	kfree(xbuff);
+	kfree(rbuff);
+	return err;
+}
+
+/* Free a SLIP channel buffers. */
+static void sl_free_bufs(struct slip *sl)
+{
+	/* Free all SLIP frame buffers. */
+	kfree(xchg(&sl->rbuff, NULL));
+	kfree(xchg(&sl->xbuff, NULL));
+#ifdef SL_INCLUDE_CSLIP
+	kfree(xchg(&sl->cbuff, NULL));
+	slhc_free(xchg(&sl->slcomp, NULL));
+#endif
+}
+
+/*
+   Reallocate slip channel buffers.
+ */
+
+static int sl_realloc_bufs(struct slip *sl, int mtu)
+{
+	int err = 0;
+	struct net_device *dev = sl->dev;
+	unsigned char *xbuff, *rbuff;
+#ifdef SL_INCLUDE_CSLIP
+	unsigned char *cbuff;
+#endif
+	int len = mtu * 2;
+
+/*
+ * allow for arrival of larger UDP packets, even if we say not to
+ * also fixes a bug in which SunOS sends 512-byte packets even with
+ * an MSS of 128
+ */
+	if (len < 576 * 2)
+		len = 576 * 2;
+
+	xbuff = kmalloc(len + 4, GFP_ATOMIC);
+	rbuff = kmalloc(len + 4, GFP_ATOMIC);
+#ifdef SL_INCLUDE_CSLIP
+	cbuff = kmalloc(len + 4, GFP_ATOMIC);
+#endif
+
+
+#ifdef SL_INCLUDE_CSLIP
+	if (xbuff == NULL || rbuff == NULL || cbuff == NULL)  {
+#else
+	if (xbuff == NULL || rbuff == NULL)  {
+#endif
+		if (mtu > sl->mtu) {
+			printk(KERN_WARNING "%s: unable to grow slip buffers, MTU change cancelled.\n",
+			       dev->name);
+			err = -ENOBUFS;
+		}
+		goto done;
+	}
+	spin_lock_bh(&sl->lock);
+
+	err = -ENODEV;
+	if (sl->tty == NULL)
+		goto done_on_bh;
+
+	xbuff    = xchg(&sl->xbuff, xbuff);
+	rbuff    = xchg(&sl->rbuff, rbuff);
+#ifdef SL_INCLUDE_CSLIP
+	cbuff    = xchg(&sl->cbuff, cbuff);
+#endif
+	if (sl->xleft)  {
+		if (sl->xleft <= len)  {
+			memcpy(sl->xbuff, sl->xhead, sl->xleft);
+		} else  {
+			sl->xleft = 0;
+			dev->stats.tx_dropped++;
+		}
+	}
+	sl->xhead = sl->xbuff;
+
+	if (sl->rcount)  {
+		if (sl->rcount <= len) {
+			memcpy(sl->rbuff, rbuff, sl->rcount);
+		} else  {
+			sl->rcount = 0;
+			dev->stats.rx_over_errors++;
+			set_bit(SLF_ERROR, &sl->flags);
+		}
+	}
+	sl->mtu      = mtu;
+	dev->mtu      = mtu;
+	sl->buffsize = len;
+	err = 0;
+
+done_on_bh:
+	spin_unlock_bh(&sl->lock);
+
+done:
+	kfree(xbuff);
+	kfree(rbuff);
+#ifdef SL_INCLUDE_CSLIP
+	kfree(cbuff);
+#endif
+	return err;
+}
+
+
+/* Set the "sending" flag.  This must be atomic hence the set_bit. */
+static inline void sl_lock(struct slip *sl)
+{
+	netif_stop_queue(sl->dev);
+}
+
+
+/* Clear the "sending" flag.  This must be atomic, hence the ASM. */
+static inline void sl_unlock(struct slip *sl)
+{
+	netif_wake_queue(sl->dev);
+}
+
+/* Send one completely decapsulated IP datagram to the IP layer. */
+static void sl_bump(struct slip *sl)
+{
+	struct net_device *dev = sl->dev;
+	struct sk_buff *skb;
+	int count;
+
+	count = sl->rcount;
+#ifdef SL_INCLUDE_CSLIP
+	if (sl->mode & (SL_MODE_ADAPTIVE | SL_MODE_CSLIP)) {
+		unsigned char c = sl->rbuff[0];
+		if (c & SL_TYPE_COMPRESSED_TCP) {
+			/* ignore compressed packets when CSLIP is off */
+			if (!(sl->mode & SL_MODE_CSLIP)) {
+				printk(KERN_WARNING "%s: compressed packet ignored\n", dev->name);
+				return;
+			}
+			/* make sure we've reserved enough space for uncompress
+			   to use */
+			if (count + 80 > sl->buffsize) {
+				dev->stats.rx_over_errors++;
+				return;
+			}
+			count = slhc_uncompress(sl->slcomp, sl->rbuff, count);
+			if (count <= 0)
+				return;
+		} else if (c >= SL_TYPE_UNCOMPRESSED_TCP) {
+			if (!(sl->mode & SL_MODE_CSLIP)) {
+				/* turn on header compression */
+				sl->mode |= SL_MODE_CSLIP;
+				sl->mode &= ~SL_MODE_ADAPTIVE;
+				printk(KERN_INFO "%s: header compression turned on\n", dev->name);
+			}
+			sl->rbuff[0] &= 0x4f;
+			if (slhc_remember(sl->slcomp, sl->rbuff, count) <= 0)
+				return;
+		}
+	}
+#endif  /* SL_INCLUDE_CSLIP */
+
+	dev->stats.rx_bytes += count;
+
+	skb = dev_alloc_skb(count);
+	if (skb == NULL) {
+		printk(KERN_WARNING "%s: memory squeeze, dropping packet.\n", dev->name);
+		dev->stats.rx_dropped++;
+		return;
+	}
+	skb->dev = dev;
+	skb_put_data(skb, sl->rbuff, count);
+	skb_reset_mac_header(skb);
+	skb->protocol = htons(ETH_P_IP);
+	netif_rx(skb);
+	dev->stats.rx_packets++;
+}
+
+/* Encapsulate one IP datagram and stuff into a TTY queue. */
+static void sl_encaps(struct slip *sl, unsigned char *icp, int len)
+{
+	unsigned char *p;
+	int actual, count;
+
+	if (len > sl->mtu) {		/* Sigh, shouldn't occur BUT ... */
+		printk(KERN_WARNING "%s: truncating oversized transmit packet!\n", sl->dev->name);
+		sl->dev->stats.tx_dropped++;
+		sl_unlock(sl);
+		return;
+	}
+
+	p = icp;
+#ifdef SL_INCLUDE_CSLIP
+	if (sl->mode & SL_MODE_CSLIP)
+		len = slhc_compress(sl->slcomp, p, len, sl->cbuff, &p, 1);
+#endif
+#ifdef CONFIG_SLIP_MODE_SLIP6
+	if (sl->mode & SL_MODE_SLIP6)
+		count = slip_esc6(p, sl->xbuff, len);
+	else
+#endif
+		count = slip_esc(p, sl->xbuff, len);
+
+	/* Order of next two lines is *very* important.
+	 * When we are sending a little amount of data,
+	 * the transfer may be completed inside the ops->write()
+	 * routine, because it's running with interrupts enabled.
+	 * In this case we *never* got WRITE_WAKEUP event,
+	 * if we did not request it before write operation.
+	 *       14 Oct 1994  Dmitry Gorodchanin.
+	 */
+	set_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+	actual = sl->tty->ops->write(sl->tty, sl->xbuff, count);
+#ifdef SL_CHECK_TRANSMIT
+	netif_trans_update(sl->dev);
+#endif
+	sl->xleft = count - actual;
+	sl->xhead = sl->xbuff + actual;
+#ifdef CONFIG_SLIP_SMART
+	/* VSV */
+	clear_bit(SLF_OUTWAIT, &sl->flags);	/* reset outfill flag */
+#endif
+}
+
+/* Write out any remaining transmit buffer. Scheduled when tty is writable */
+static void slip_transmit(struct work_struct *work)
+{
+	struct slip *sl = container_of(work, struct slip, tx_work);
+	int actual;
+
+	spin_lock_bh(&sl->lock);
+	/* First make sure we're connected. */
+	if (!sl->tty || sl->magic != SLIP_MAGIC || !netif_running(sl->dev)) {
+		spin_unlock_bh(&sl->lock);
+		return;
+	}
+
+	if (sl->xleft <= 0)  {
+		/* Now serial buffer is almost free & we can start
+		 * transmission of another packet */
+		sl->dev->stats.tx_packets++;
+		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+		spin_unlock_bh(&sl->lock);
+		sl_unlock(sl);
+		return;
+	}
+
+	actual = sl->tty->ops->write(sl->tty, sl->xhead, sl->xleft);
+	sl->xleft -= actual;
+	sl->xhead += actual;
+	spin_unlock_bh(&sl->lock);
+}
+
+/*
+ * Called by the driver when there's room for more data.
+ * Schedule the transmit.
+ */
+static void slip_write_wakeup(struct tty_struct *tty)
+{
+	struct slip *sl;
+
+	rcu_read_lock();
+	sl = rcu_dereference(tty->disc_data);
+	if (sl)
+		schedule_work(&sl->tx_work);
+	rcu_read_unlock();
+}
+
+static void sl_tx_timeout(struct net_device *dev, unsigned int txqueue)
+{
+	struct slip *sl = netdev_priv(dev);
+
+	spin_lock(&sl->lock);
+
+	if (netif_queue_stopped(dev)) {
+		if (!netif_running(dev) || !sl->tty)
+			goto out;
+
+		/* May be we must check transmitter timeout here ?
+		 *      14 Oct 1994 Dmitry Gorodchanin.
+		 */
+#ifdef SL_CHECK_TRANSMIT
+		if (time_before(jiffies, dev_trans_start(dev) + 20 * HZ))  {
+			/* 20 sec timeout not reached */
+			goto out;
+		}
+		printk(KERN_WARNING "%s: transmit timed out, %s?\n",
+			dev->name,
+			(tty_chars_in_buffer(sl->tty) || sl->xleft) ?
+				"bad line quality" : "driver error");
+		sl->xleft = 0;
+		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+		sl_unlock(sl);
+#endif
+	}
+out:
+	spin_unlock(&sl->lock);
+}
+
+
+/* Encapsulate an IP datagram and kick it into a TTY queue. */
+static netdev_tx_t
+sl_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct slip *sl = netdev_priv(dev);
+
+	spin_lock(&sl->lock);
+	if (!netif_running(dev)) {
+		spin_unlock(&sl->lock);
+		printk(KERN_WARNING "%s: xmit call when iface is down\n", dev->name);
+		dev_kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
+	if (sl->tty == NULL) {
+		spin_unlock(&sl->lock);
+		dev_kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
+
+	sl_lock(sl);
+	dev->stats.tx_bytes += skb->len;
+	sl_encaps(sl, skb->data, skb->len);
+	spin_unlock(&sl->lock);
+
+	dev_kfree_skb(skb);
+	return NETDEV_TX_OK;
+}
+
+
+/******************************************
+ *   Routines looking at netdevice side.
+ ******************************************/
+
+/* Netdevice UP -> DOWN routine */
+
+static int
+sl_close(struct net_device *dev)
+{
+	struct slip *sl = netdev_priv(dev);
+
+	spin_lock_bh(&sl->lock);
+	if (sl->tty)
+		/* TTY discipline is running. */
+		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+	netif_stop_queue(dev);
+	sl->rcount   = 0;
+	sl->xleft    = 0;
+	spin_unlock_bh(&sl->lock);
+
+	return 0;
+}
+
+/* Netdevice DOWN -> UP routine */
+
+static int sl_open(struct net_device *dev)
+{
+	struct slip *sl = netdev_priv(dev);
+
+	if (sl->tty == NULL)
+		return -ENODEV;
+
+	sl->flags &= (1 << SLF_INUSE);
+	netif_start_queue(dev);
+	return 0;
+}
+
+/* Netdevice change MTU request */
+
+static int sl_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct slip *sl = netdev_priv(dev);
+
+	return sl_realloc_bufs(sl, new_mtu);
+}
+
+/* Netdevice get statistics request */
+
+static void
+sl_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
+{
+	struct net_device_stats *devstats = &dev->stats;
+#ifdef SL_INCLUDE_CSLIP
+	struct slip *sl = netdev_priv(dev);
+	struct slcompress *comp = sl->slcomp;
+#endif
+	stats->rx_packets     = devstats->rx_packets;
+	stats->tx_packets     = devstats->tx_packets;
+	stats->rx_bytes       = devstats->rx_bytes;
+	stats->tx_bytes       = devstats->tx_bytes;
+	stats->rx_dropped     = devstats->rx_dropped;
+	stats->tx_dropped     = devstats->tx_dropped;
+	stats->tx_errors      = devstats->tx_errors;
+	stats->rx_errors      = devstats->rx_errors;
+	stats->rx_over_errors = devstats->rx_over_errors;
+
+#ifdef SL_INCLUDE_CSLIP
+	if (comp) {
+		/* Generic compressed statistics */
+		stats->rx_compressed   = comp->sls_i_compressed;
+		stats->tx_compressed   = comp->sls_o_compressed;
+
+		/* Are we really still needs this? */
+		stats->rx_fifo_errors += comp->sls_i_compressed;
+		stats->rx_dropped     += comp->sls_i_tossed;
+		stats->tx_fifo_errors += comp->sls_o_compressed;
+		stats->collisions     += comp->sls_o_misses;
+	}
+#endif
+}
+
+/* Netdevice register callback */
+
+static int sl_init(struct net_device *dev)
+{
+	struct slip *sl = netdev_priv(dev);
+
+	/*
+	 *	Finish setting up the DEVICE info.
+	 */
+
+	dev->mtu		= sl->mtu;
+	dev->type		= ARPHRD_SLIP + sl->mode;
+#ifdef SL_CHECK_TRANSMIT
+	dev->watchdog_timeo	= 20*HZ;
+#endif
+	return 0;
+}
+
+
+static void sl_uninit(struct net_device *dev)
+{
+	struct slip *sl = netdev_priv(dev);
+
+	sl_free_bufs(sl);
+}
+
+/* Hook the destructor so we can free slip devices at the right point in time */
+static void sl_free_netdev(struct net_device *dev)
+{
+	int i = dev->base_addr;
+
+	slip_devs[i] = NULL;
+}
+
+static const struct net_device_ops sl_netdev_ops = {
+	.ndo_init		= sl_init,
+	.ndo_uninit	  	= sl_uninit,
+	.ndo_open		= sl_open,
+	.ndo_stop		= sl_close,
+	.ndo_start_xmit		= sl_xmit,
+	.ndo_get_stats64        = sl_get_stats64,
+	.ndo_change_mtu		= sl_change_mtu,
+	.ndo_tx_timeout		= sl_tx_timeout,
+#ifdef CONFIG_SLIP_SMART
+	.ndo_siocdevprivate	= sl_siocdevprivate,
+#endif
+};
+
+
+static void sl_setup(struct net_device *dev)
+{
+	dev->netdev_ops		= &sl_netdev_ops;
+	dev->needs_free_netdev	= true;
+	dev->priv_destructor	= sl_free_netdev;
+
+	dev->hard_header_len	= 0;
+	dev->addr_len		= 0;
+	dev->tx_queue_len	= 10;
+
+	/* MTU range: 68 - 65534 */
+	dev->min_mtu = 68;
+	dev->max_mtu = 65534;
+
+	/* New-style flags. */
+	dev->flags		= IFF_NOARP|IFF_POINTOPOINT|IFF_MULTICAST;
+}
+
+/******************************************
+  Routines looking at TTY side.
+ ******************************************/
+
+
+/*
+ * Handle the 'receiver data ready' interrupt.
+ * This function is called by the 'tty_io' module in the kernel when
+ * a block of SLIP data has been received, which can now be decapsulated
+ * and sent on to some IP layer for further processing. This will not
+ * be re-entered while running but other ldisc functions may be called
+ * in parallel
+ */
+
+static void slip_receive_buf(struct tty_struct *tty, const unsigned char *cp,
+		const char *fp, int count)
+{
+	struct slip *sl = tty->disc_data;
+
+	if (!sl || sl->magic != SLIP_MAGIC || !netif_running(sl->dev))
+		return;
+
+	/* Read the characters out of the buffer */
+	while (count--) {
+		if (fp && *fp++) {
+			if (!test_and_set_bit(SLF_ERROR, &sl->flags))
+				sl->dev->stats.rx_errors++;
+			cp++;
+			continue;
+		}
+#ifdef CONFIG_SLIP_MODE_SLIP6
+		if (sl->mode & SL_MODE_SLIP6)
+			slip_unesc6(sl, *cp++);
+		else
+#endif
+			slip_unesc(sl, *cp++);
+	}
+}
+
+/************************************
+ *  slip_open helper routines.
+ ************************************/
+
+/* Collect hanged up channels */
+static void sl_sync(void)
+{
+	int i;
+	struct net_device *dev;
+	struct slip	  *sl;
+
+	for (i = 0; i < slip_maxdev; i++) {
+		dev = slip_devs[i];
+		if (dev == NULL)
+			break;
+
+		sl = netdev_priv(dev);
+		if (sl->tty || sl->leased)
+			continue;
+		if (dev->flags & IFF_UP)
+			dev_close(dev);
+	}
+}
+
+
+/* Find a free SLIP channel, and link in this `tty' line. */
+static struct slip *sl_alloc(void)
+{
+	int i;
+	char name[IFNAMSIZ];
+	struct net_device *dev = NULL;
+	struct slip       *sl;
+
+	for (i = 0; i < slip_maxdev; i++) {
+		dev = slip_devs[i];
+		if (dev == NULL)
+			break;
+	}
+	/* Sorry, too many, all slots in use */
+	if (i >= slip_maxdev)
+		return NULL;
+
+	sprintf(name, "sl%d", i);
+	dev = alloc_netdev(sizeof(*sl), name, NET_NAME_UNKNOWN, sl_setup);
+	if (!dev)
+		return NULL;
+
+	dev->base_addr  = i;
+	sl = netdev_priv(dev);
+
+	/* Initialize channel control data */
+	sl->magic       = SLIP_MAGIC;
+	sl->dev	      	= dev;
+	spin_lock_init(&sl->lock);
+	INIT_WORK(&sl->tx_work, slip_transmit);
+	sl->mode        = SL_MODE_DEFAULT;
+#ifdef CONFIG_SLIP_SMART
+	/* initialize timer_list struct */
+	timer_setup(&sl->keepalive_timer, sl_keepalive, 0);
+	timer_setup(&sl->outfill_timer, sl_outfill, 0);
+#endif
+	slip_devs[i] = dev;
+	return sl;
+}
+
+/*
+ * Open the high-level part of the SLIP channel.
+ * This function is called by the TTY module when the
+ * SLIP line discipline is called for.  Because we are
+ * sure the tty line exists, we only have to link it to
+ * a free SLIP channel...
+ *
+ * Called in process context serialized from other ldisc calls.
+ */
+
+static int slip_open(struct tty_struct *tty)
+{
+	struct slip *sl;
+	int err;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (tty->ops->write == NULL)
+		return -EOPNOTSUPP;
+
+	/* RTnetlink lock is misused here to serialize concurrent
+	   opens of slip channels. There are better ways, but it is
+	   the simplest one.
+	 */
+	rtnl_lock();
+
+	/* Collect hanged up channels. */
+	sl_sync();
+
+	sl = tty->disc_data;
+
+	err = -EEXIST;
+	/* First make sure we're not already connected. */
+	if (sl && sl->magic == SLIP_MAGIC)
+		goto err_exit;
+
+	/* OK.  Find a free SLIP channel to use. */
+	err = -ENFILE;
+	sl = sl_alloc();
+	if (sl == NULL)
+		goto err_exit;
+
+	sl->tty = tty;
+	tty->disc_data = sl;
+	sl->pid = current->pid;
+
+	if (!test_bit(SLF_INUSE, &sl->flags)) {
+		/* Perform the low-level SLIP initialization. */
+		err = sl_alloc_bufs(sl, SL_MTU);
+		if (err)
+			goto err_free_chan;
+
+		set_bit(SLF_INUSE, &sl->flags);
+
+		err = register_netdevice(sl->dev);
+		if (err)
+			goto err_free_bufs;
+	}
+
+#ifdef CONFIG_SLIP_SMART
+	if (sl->keepalive) {
+		sl->keepalive_timer.expires = jiffies + sl->keepalive * HZ;
+		add_timer(&sl->keepalive_timer);
+	}
+	if (sl->outfill) {
+		sl->outfill_timer.expires = jiffies + sl->outfill * HZ;
+		add_timer(&sl->outfill_timer);
+	}
+#endif
+
+	/* Done.  We have linked the TTY line to a channel. */
+	rtnl_unlock();
+	tty->receive_room = 65536;	/* We don't flow control */
+
+	/* TTY layer expects 0 on success */
+	return 0;
+
+err_free_bufs:
+	sl_free_bufs(sl);
+
+err_free_chan:
+	sl->tty = NULL;
+	tty->disc_data = NULL;
+	clear_bit(SLF_INUSE, &sl->flags);
+	sl_free_netdev(sl->dev);
+	/* do not call free_netdev before rtnl_unlock */
+	rtnl_unlock();
+	free_netdev(sl->dev);
+	return err;
+
+err_exit:
+	rtnl_unlock();
+
+	/* Count references from TTY module */
+	return err;
+}
+
+/*
+ * Close down a SLIP channel.
+ * This means flushing out any pending queues, and then returning. This
+ * call is serialized against other ldisc functions.
+ *
+ * We also use this method fo a hangup event
+ */
+
+static void slip_close(struct tty_struct *tty)
+{
+	struct slip *sl = tty->disc_data;
+
+	/* First make sure we're connected. */
+	if (!sl || sl->magic != SLIP_MAGIC || sl->tty != tty)
+		return;
+
+	spin_lock_bh(&sl->lock);
+	rcu_assign_pointer(tty->disc_data, NULL);
+	sl->tty = NULL;
+	spin_unlock_bh(&sl->lock);
+
+	synchronize_rcu();
+	flush_work(&sl->tx_work);
+
+	/* VSV = very important to remove timers */
+#ifdef CONFIG_SLIP_SMART
+	del_timer_sync(&sl->keepalive_timer);
+	del_timer_sync(&sl->outfill_timer);
+#endif
+	/* Flush network side */
+	unregister_netdev(sl->dev);
+	/* This will complete via sl_free_netdev */
+}
+
+static void slip_hangup(struct tty_struct *tty)
+{
+	slip_close(tty);
+}
+ /************************************************************************
+  *			STANDARD SLIP ENCAPSULATION		  	 *
+  ************************************************************************/
+
+static int slip_esc(unsigned char *s, unsigned char *d, int len)
+{
+	unsigned char *ptr = d;
+	unsigned char c;
+
+	/*
+	 * Send an initial END character to flush out any
+	 * data that may have accumulated in the receiver
+	 * due to line noise.
+	 */
+
+	*ptr++ = END;
+
+	/*
+	 * For each byte in the packet, send the appropriate
+	 * character sequence, according to the SLIP protocol.
+	 */
+
+	while (len-- > 0) {
+		switch (c = *s++) {
+		case END:
+			*ptr++ = ESC;
+			*ptr++ = ESC_END;
+			break;
+		case ESC:
+			*ptr++ = ESC;
+			*ptr++ = ESC_ESC;
+			break;
+		default:
+			*ptr++ = c;
+			break;
+		}
+	}
+	*ptr++ = END;
+	return ptr - d;
+}
+
+static void slip_unesc(struct slip *sl, unsigned char s)
+{
+
+	switch (s) {
+	case END:
+#ifdef CONFIG_SLIP_SMART
+		/* drop keeptest bit = VSV */
+		if (test_bit(SLF_KEEPTEST, &sl->flags))
+			clear_bit(SLF_KEEPTEST, &sl->flags);
+#endif
+
+		if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
+		    (sl->rcount > 2))
+			sl_bump(sl);
+		clear_bit(SLF_ESCAPE, &sl->flags);
+		sl->rcount = 0;
+		return;
+
+	case ESC:
+		set_bit(SLF_ESCAPE, &sl->flags);
+		return;
+	case ESC_ESC:
+		if (test_and_clear_bit(SLF_ESCAPE, &sl->flags))
+			s = ESC;
+		break;
+	case ESC_END:
+		if (test_and_clear_bit(SLF_ESCAPE, &sl->flags))
+			s = END;
+		break;
+	}
+	if (!test_bit(SLF_ERROR, &sl->flags))  {
+		if (sl->rcount < sl->buffsize)  {
+			sl->rbuff[sl->rcount++] = s;
+			return;
+		}
+		sl->dev->stats.rx_over_errors++;
+		set_bit(SLF_ERROR, &sl->flags);
+	}
+}
+
+
+#ifdef CONFIG_SLIP_MODE_SLIP6
+/************************************************************************
+ *			 6 BIT SLIP ENCAPSULATION			*
+ ************************************************************************/
+
+static int slip_esc6(unsigned char *s, unsigned char *d, int len)
+{
+	unsigned char *ptr = d;
+	unsigned char c;
+	int i;
+	unsigned short v = 0;
+	short bits = 0;
+
+	/*
+	 * Send an initial END character to flush out any
+	 * data that may have accumulated in the receiver
+	 * due to line noise.
+	 */
+
+	*ptr++ = 0x70;
+
+	/*
+	 * Encode the packet into printable ascii characters
+	 */
+
+	for (i = 0; i < len; ++i) {
+		v = (v << 8) | s[i];
+		bits += 8;
+		while (bits >= 6) {
+			bits -= 6;
+			c = 0x30 + ((v >> bits) & 0x3F);
+			*ptr++ = c;
+		}
+	}
+	if (bits) {
+		c = 0x30 + ((v << (6 - bits)) & 0x3F);
+		*ptr++ = c;
+	}
+	*ptr++ = 0x70;
+	return ptr - d;
+}
+
+static void slip_unesc6(struct slip *sl, unsigned char s)
+{
+	unsigned char c;
+
+	if (s == 0x70) {
+#ifdef CONFIG_SLIP_SMART
+		/* drop keeptest bit = VSV */
+		if (test_bit(SLF_KEEPTEST, &sl->flags))
+			clear_bit(SLF_KEEPTEST, &sl->flags);
+#endif
+
+		if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
+		    (sl->rcount > 2))
+			sl_bump(sl);
+		sl->rcount = 0;
+		sl->xbits = 0;
+		sl->xdata = 0;
+	} else if (s >= 0x30 && s < 0x70) {
+		sl->xdata = (sl->xdata << 6) | ((s - 0x30) & 0x3F);
+		sl->xbits += 6;
+		if (sl->xbits >= 8) {
+			sl->xbits -= 8;
+			c = (unsigned char)(sl->xdata >> sl->xbits);
+			if (!test_bit(SLF_ERROR, &sl->flags))  {
+				if (sl->rcount < sl->buffsize)  {
+					sl->rbuff[sl->rcount++] = c;
+					return;
+				}
+				sl->dev->stats.rx_over_errors++;
+				set_bit(SLF_ERROR, &sl->flags);
+			}
+		}
+	}
+}
+#endif /* CONFIG_SLIP_MODE_SLIP6 */
+
+/* Perform I/O control on an active SLIP channel. */
+static int slip_ioctl(struct tty_struct *tty, unsigned int cmd,
+		unsigned long arg)
+{
+	struct slip *sl = tty->disc_data;
+	unsigned int tmp;
+	int __user *p = (int __user *)arg;
+
+	/* First make sure we're connected. */
+	if (!sl || sl->magic != SLIP_MAGIC)
+		return -EINVAL;
+
+	switch (cmd) {
+	case SIOCGIFNAME:
+		tmp = strlen(sl->dev->name) + 1;
+		if (copy_to_user((void __user *)arg, sl->dev->name, tmp))
+			return -EFAULT;
+		return 0;
+
+	case SIOCGIFENCAP:
+		if (put_user(sl->mode, p))
+			return -EFAULT;
+		return 0;
+
+	case SIOCSIFENCAP:
+		if (get_user(tmp, p))
+			return -EFAULT;
+#ifndef SL_INCLUDE_CSLIP
+		if (tmp & (SL_MODE_CSLIP|SL_MODE_ADAPTIVE))
+			return -EINVAL;
+#else
+		if ((tmp & (SL_MODE_ADAPTIVE | SL_MODE_CSLIP)) ==
+		    (SL_MODE_ADAPTIVE | SL_MODE_CSLIP))
+			/* return -EINVAL; */
+			tmp &= ~SL_MODE_ADAPTIVE;
+#endif
+#ifndef CONFIG_SLIP_MODE_SLIP6
+		if (tmp & SL_MODE_SLIP6)
+			return -EINVAL;
+#endif
+		sl->mode = tmp;
+		sl->dev->type = ARPHRD_SLIP + sl->mode;
+		return 0;
+
+	case SIOCSIFHWADDR:
+		return -EINVAL;
+
+#ifdef CONFIG_SLIP_SMART
+	/* VSV changes start here */
+	case SIOCSKEEPALIVE:
+		if (get_user(tmp, p))
+			return -EFAULT;
+		if (tmp > 255) /* max for unchar */
+			return -EINVAL;
+
+		spin_lock_bh(&sl->lock);
+		if (!sl->tty) {
+			spin_unlock_bh(&sl->lock);
+			return -ENODEV;
+		}
+		sl->keepalive = (u8)tmp;
+		if (sl->keepalive != 0) {
+			mod_timer(&sl->keepalive_timer,
+					jiffies + sl->keepalive * HZ);
+			set_bit(SLF_KEEPTEST, &sl->flags);
+		} else
+			del_timer(&sl->keepalive_timer);
+		spin_unlock_bh(&sl->lock);
+		return 0;
+
+	case SIOCGKEEPALIVE:
+		if (put_user(sl->keepalive, p))
+			return -EFAULT;
+		return 0;
+
+	case SIOCSOUTFILL:
+		if (get_user(tmp, p))
+			return -EFAULT;
+		if (tmp > 255) /* max for unchar */
+			return -EINVAL;
+		spin_lock_bh(&sl->lock);
+		if (!sl->tty) {
+			spin_unlock_bh(&sl->lock);
+			return -ENODEV;
+		}
+		sl->outfill = (u8)tmp;
+		if (sl->outfill != 0) {
+			mod_timer(&sl->outfill_timer,
+						jiffies + sl->outfill * HZ);
+			set_bit(SLF_OUTWAIT, &sl->flags);
+		} else
+			del_timer(&sl->outfill_timer);
+		spin_unlock_bh(&sl->lock);
+		return 0;
+
+	case SIOCGOUTFILL:
+		if (put_user(sl->outfill, p))
+			return -EFAULT;
+		return 0;
+	/* VSV changes end */
+#endif
+	default:
+		return tty_mode_ioctl(tty, cmd, arg);
+	}
+}
+
+/* VSV changes start here */
+#ifdef CONFIG_SLIP_SMART
+/* function sl_siocdevprivate called from net/core/dev.c
+   to allow get/set outfill/keepalive parameter
+   by ifconfig                                 */
+
+static int sl_siocdevprivate(struct net_device *dev, struct ifreq *rq,
+			     void __user *data, int cmd)
+{
+	struct slip *sl = netdev_priv(dev);
+	unsigned long *p = (unsigned long *)&rq->ifr_ifru;
+
+	if (sl == NULL)		/* Allocation failed ?? */
+		return -ENODEV;
+
+	if (in_compat_syscall())
+		return -EOPNOTSUPP;
+
+	spin_lock_bh(&sl->lock);
+
+	if (!sl->tty) {
+		spin_unlock_bh(&sl->lock);
+		return -ENODEV;
+	}
+
+	switch (cmd) {
+	case SIOCSKEEPALIVE:
+		/* max for unchar */
+		if ((unsigned)*p > 255) {
+			spin_unlock_bh(&sl->lock);
+			return -EINVAL;
+		}
+		sl->keepalive = (u8)*p;
+		if (sl->keepalive != 0) {
+			sl->keepalive_timer.expires =
+						jiffies + sl->keepalive * HZ;
+			mod_timer(&sl->keepalive_timer,
+						jiffies + sl->keepalive * HZ);
+			set_bit(SLF_KEEPTEST, &sl->flags);
+		} else
+			del_timer(&sl->keepalive_timer);
+		break;
+
+	case SIOCGKEEPALIVE:
+		*p = sl->keepalive;
+		break;
+
+	case SIOCSOUTFILL:
+		if ((unsigned)*p > 255) { /* max for unchar */
+			spin_unlock_bh(&sl->lock);
+			return -EINVAL;
+		}
+		sl->outfill = (u8)*p;
+		if (sl->outfill != 0) {
+			mod_timer(&sl->outfill_timer,
+						jiffies + sl->outfill * HZ);
+			set_bit(SLF_OUTWAIT, &sl->flags);
+		} else
+			del_timer(&sl->outfill_timer);
+		break;
+
+	case SIOCGOUTFILL:
+		*p = sl->outfill;
+		break;
+
+	case SIOCSLEASE:
+		/* Resolve race condition, when ioctl'ing hanged up
+		   and opened by another process device.
+		 */
+		if (sl->tty != current->signal->tty &&
+						sl->pid != current->pid) {
+			spin_unlock_bh(&sl->lock);
+			return -EPERM;
+		}
+		sl->leased = 0;
+		if (*p)
+			sl->leased = 1;
+		break;
+
+	case SIOCGLEASE:
+		*p = sl->leased;
+	}
+	spin_unlock_bh(&sl->lock);
+	return 0;
+}
+#endif
+/* VSV changes end */
+
+static struct tty_ldisc_ops sl_ldisc = {
+	.owner 		= THIS_MODULE,
+	.num		= N_SLIP,
+	.name 		= "slip",
+	.open 		= slip_open,
+	.close	 	= slip_close,
+	.hangup	 	= slip_hangup,
+	.ioctl		= slip_ioctl,
+	.receive_buf	= slip_receive_buf,
+	.write_wakeup	= slip_write_wakeup,
+};
+
+static int __init slip_init(void)
+{
+	int status;
+
+	if (slip_maxdev < 4)
+		slip_maxdev = 4; /* Sanity */
+
+	printk(KERN_INFO "SLIP: version %s (dynamic channels, max=%d)"
+#ifdef CONFIG_SLIP_MODE_SLIP6
+	       " (6 bit encapsulation enabled)"
+#endif
+	       ".\n",
+	       SLIP_VERSION, slip_maxdev);
+#if defined(SL_INCLUDE_CSLIP)
+	printk(KERN_INFO "CSLIP: code copyright 1989 Regents of the University of California.\n");
+#endif
+#ifdef CONFIG_SLIP_SMART
+	printk(KERN_INFO "SLIP linefill/keepalive option.\n");
+#endif
+
+	slip_devs = kcalloc(slip_maxdev, sizeof(struct net_device *),
+								GFP_KERNEL);
+	if (!slip_devs)
+		return -ENOMEM;
+
+	/* Fill in our line protocol discipline, and register it */
+	status = tty_register_ldisc(&sl_ldisc);
+	if (status != 0) {
+		printk(KERN_ERR "SLIP: can't register line discipline (err = %d)\n", status);
+		kfree(slip_devs);
+	}
+	return status;
+}
+
+static void __exit slip_exit(void)
+{
+	int i;
+	struct net_device *dev;
+	struct slip *sl;
+	unsigned long timeout = jiffies + HZ;
+	int busy = 0;
+
+	if (slip_devs == NULL)
+		return;
+
+	/* First of all: check for active disciplines and hangup them.
+	 */
+	do {
+		if (busy)
+			msleep_interruptible(100);
+
+		busy = 0;
+		for (i = 0; i < slip_maxdev; i++) {
+			dev = slip_devs[i];
+			if (!dev)
+				continue;
+			sl = netdev_priv(dev);
+			spin_lock_bh(&sl->lock);
+			if (sl->tty) {
+				busy++;
+				tty_hangup(sl->tty);
+			}
+			spin_unlock_bh(&sl->lock);
+		}
+	} while (busy && time_before(jiffies, timeout));
+
+	/* FIXME: hangup is async so we should wait when doing this second
+	   phase */
+
+	for (i = 0; i < slip_maxdev; i++) {
+		dev = slip_devs[i];
+		if (!dev)
+			continue;
+		slip_devs[i] = NULL;
+
+		sl = netdev_priv(dev);
+		if (sl->tty) {
+			printk(KERN_ERR "%s: tty discipline still running\n",
+			       dev->name);
+		}
+
+		unregister_netdev(dev);
+	}
+
+	kfree(slip_devs);
+	slip_devs = NULL;
+
+	tty_unregister_ldisc(&sl_ldisc);
+}
+
+module_init(slip_init);
+module_exit(slip_exit);
+
+#ifdef CONFIG_SLIP_SMART
+/*
+ * This is start of the code for multislip style line checking
+ * added by Stanislav Voronyi. All changes before marked VSV
+ */
+
+static void sl_outfill(struct timer_list *t)
+{
+	struct slip *sl = from_timer(sl, t, outfill_timer);
+
+	spin_lock(&sl->lock);
+
+	if (sl->tty == NULL)
+		goto out;
+
+	if (sl->outfill) {
+		if (test_bit(SLF_OUTWAIT, &sl->flags)) {
+			/* no packets were transmitted, do outfill */
+#ifdef CONFIG_SLIP_MODE_SLIP6
+			unsigned char s = (sl->mode & SL_MODE_SLIP6)?0x70:END;
+#else
+			unsigned char s = END;
+#endif
+			/* put END into tty queue. Is it right ??? */
+			if (!netif_queue_stopped(sl->dev)) {
+				/* if device busy no outfill */
+				sl->tty->ops->write(sl->tty, &s, 1);
+			}
+		} else
+			set_bit(SLF_OUTWAIT, &sl->flags);
+
+		mod_timer(&sl->outfill_timer, jiffies+sl->outfill*HZ);
+	}
+out:
+	spin_unlock(&sl->lock);
+}
+
+static void sl_keepalive(struct timer_list *t)
+{
+	struct slip *sl = from_timer(sl, t, keepalive_timer);
+
+	spin_lock(&sl->lock);
+
+	if (sl->tty == NULL)
+		goto out;
+
+	if (sl->keepalive) {
+		if (test_bit(SLF_KEEPTEST, &sl->flags)) {
+			/* keepalive still high :(, we must hangup */
+			if (sl->outfill)
+				/* outfill timer must be deleted too */
+				(void)del_timer(&sl->outfill_timer);
+			printk(KERN_DEBUG "%s: no packets received during keepalive timeout, hangup.\n", sl->dev->name);
+			/* this must hangup tty & close slip */
+			tty_hangup(sl->tty);
+			/* I think we need not something else */
+			goto out;
+		} else
+			set_bit(SLF_KEEPTEST, &sl->flags);
+
+		mod_timer(&sl->keepalive_timer, jiffies+sl->keepalive*HZ);
+	}
+out:
+	spin_unlock(&sl->lock);
+}
+
+#endif
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_LDISC(N_SLIP);
diff --git a/drivers/net/slip/slip.h b/drivers/net/slip/slip.h
new file mode 100644
index 000000000..3d7f88b33
--- /dev/null
+++ b/drivers/net/slip/slip.h
@@ -0,0 +1,105 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * slip.h	Define the SLIP device driver interface and constants.
+ *
+ * NOTE:	THIS FILE WILL BE MOVED TO THE LINUX INCLUDE DIRECTORY
+ *		AS SOON AS POSSIBLE!
+ *
+ * Version:	@(#)slip.h	1.2.0	03/28/93
+ *
+ * Fixes:
+ *		Alan Cox	: 	Added slip mtu field.
+ *		Matt Dillon	:	Printable slip (borrowed from net2e)
+ *		Alan Cox	:	Added SL_SLIP_LOTS
+ *	Dmitry Gorodchanin	:	A lot of changes in the 'struct slip'
+ *	Dmitry Gorodchanin	:	Added CSLIP statistics.
+ *	Stanislav Voronyi	:	Make line checking as created by
+ *					Igor Chechik, RELCOM Corp.
+ *	Craig Schlenter		:	Fixed #define bug that caused
+ *					CSLIP telnets to hang in 1.3.61-6
+ *
+ * Author:	Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
+ */
+#ifndef _LINUX_SLIP_H
+#define _LINUX_SLIP_H
+
+
+#if defined(CONFIG_INET) && defined(CONFIG_SLIP_COMPRESSED)
+# define SL_INCLUDE_CSLIP
+#endif
+
+#ifdef SL_INCLUDE_CSLIP
+# define SL_MODE_DEFAULT SL_MODE_ADAPTIVE
+#else
+# define SL_MODE_DEFAULT SL_MODE_SLIP
+#endif
+
+/* SLIP configuration. */
+#define SL_NRUNIT	256		/* MAX number of SLIP channels;
+					   This can be overridden with
+					   insmod -oslip_maxdev=nnn	*/
+#define SL_MTU		296		/* 296; I am used to 600- FvK	*/
+
+/* some arch define END as assembly function ending, just undef it */
+#undef	END
+/* SLIP protocol characters. */
+#define END             0300		/* indicates end of frame	*/
+#define ESC             0333		/* indicates byte stuffing	*/
+#define ESC_END         0334		/* ESC ESC_END means END 'data'	*/
+#define ESC_ESC         0335		/* ESC ESC_ESC means ESC 'data'	*/
+
+
+struct slip {
+  int			magic;
+
+  /* Various fields. */
+  struct tty_struct	*tty;		/* ptr to TTY structure		*/
+  struct net_device	*dev;		/* easy for intr handling	*/
+  spinlock_t		lock;
+  struct work_struct	tx_work;	/* Flushes transmit buffer	*/
+
+#ifdef SL_INCLUDE_CSLIP
+  struct slcompress	*slcomp;	/* for header compression 	*/
+  unsigned char		*cbuff;		/* compression buffer		*/
+#endif
+
+  /* These are pointers to the malloc()ed frame buffers. */
+  unsigned char		*rbuff;		/* receiver buffer		*/
+  int                   rcount;         /* received chars counter       */
+  unsigned char		*xbuff;		/* transmitter buffer		*/
+  unsigned char         *xhead;         /* pointer to next byte to XMIT */
+  int                   xleft;          /* bytes left in XMIT queue     */
+  int			mtu;		/* Our mtu (to spot changes!)   */
+  int                   buffsize;       /* Max buffers sizes            */
+
+#ifdef CONFIG_SLIP_MODE_SLIP6
+  int			xdata, xbits;	/* 6 bit slip controls 		*/
+#endif
+
+  unsigned long		flags;		/* Flag values/ mode etc	*/
+#define SLF_INUSE	0		/* Channel in use               */
+#define SLF_ESCAPE	1               /* ESC received                 */
+#define SLF_ERROR	2               /* Parity, etc. error           */
+#define SLF_KEEPTEST	3		/* Keepalive test flag		*/
+#define SLF_OUTWAIT	4		/* is outpacket was flag	*/
+
+  unsigned char		mode;		/* SLIP mode			*/
+  unsigned char		leased;
+  pid_t			pid;
+#define SL_MODE_SLIP	0
+#define SL_MODE_CSLIP	1
+#define SL_MODE_SLIP6	2		/* Matt Dillon's printable slip */
+#define SL_MODE_CSLIP6	(SL_MODE_SLIP6|SL_MODE_CSLIP)
+#define SL_MODE_AX25	4
+#define SL_MODE_ADAPTIVE 8
+#ifdef CONFIG_SLIP_SMART
+  unsigned char		outfill;	/* # of sec between outfill packet */
+  unsigned char		keepalive;	/* keepalive seconds		*/
+  struct timer_list	outfill_timer;
+  struct timer_list	keepalive_timer;
+#endif
+};
+
+#define SLIP_MAGIC 0x5302
+
+#endif	/* _LINUX_SLIP.H */