Merge patch series "can: slcan: extend supported features (step 2)"

Dario Binacchi <dario.binacchi@amarulasolutions.com> says:

====================

With this series I try to finish the task, started with the series [1],
of completely removing the dependency of the slcan driver from the
userspace slcand/slcan_attach applications.

The series also contains patches that remove the legacy stuff (slcan_devs,
SLCAN_MAGIC, ...) and do some module cleanup.

The series has been created on top of the patches:

can: slcan: convert comments to network style comments
can: slcan: slcan_init() convert printk(LEVEL ...) to pr_level()
can: slcan: fix whitespace issues
can: slcan: convert comparison to NULL into !val
can: slcan: clean up if/else
can: slcan: use scnprintf() as a hardening measure
can: slcan: do not report txerr and rxerr during bus-off
can: slcan: do not sleep with a spin lock held

applied to linux-next.

[1] https://lore.kernel.org/all/20220628163137.413025-1-dario.binacchi@amarulasolutions.com

Changes since v3: https://lore.kernel.org/all/20220726210217.3368497-1-dario.binacchi@amarulasolutions.com
- Add Max Staudt's `Reviewed-by' tag.
- Drop the patch "ethtool: add support to get/set CAN bit time register".
- Drop the patch "can: slcan: add support to set bit time register (btr)".
- Remove the RFC prefix from the series.

Changes since v2: https://lore.kernel.org/all/20220725065419.3005015-1-dario.binacchi@amarulasolutions.com
- Update the commit message.
- Use 1 space in front of the =.
- Put the series as RFC again.
- Pick up the patch "can: slcan: use KBUILD_MODNAME and define pr_fmt to replace hardcoded names".
- Add the patch "ethtool: add support to get/set CAN bit time register"
  to the series.
- Add the patch "can: slcan: add support to set bit time register (btr)"
  to the series.
- Replace the link https://marc.info/?l=linux-can&m=165806705927851&w=2 with
  https://lore.kernel.org/all/507b5973-d673-4755-3b64-b41cb9a13b6f@hartkopp.net.
- Add the `Suggested-by' tag.

Changes since RFC: https://lore.kernel.org/all/20220716170007.2020037-1-dario.binacchi@amarulasolutions.com
- Re-add headers that export at least one symbol used by the module.
- Update the commit description.
- Drop the old "slcan" name to use the standard canX interface naming.
- Remove comment on listen-only command.
- Update the commit subject and description.
- Add the patch "MAINTAINERS: Add myself as maintainer of the SLCAN driver"
  to the series.

====================

mkl: rebased to can-next/master

Link: https://lore.kernel.org/all/20220728070254.267974-1-dario.binacchi@amarulasolutions.comSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

MAINTAINERS

@@ -18470,6 +18470,12 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git
 F:	include/linux/sl?b*.h
 F:	mm/sl?b*
 
+SLCAN CAN NETWORK DRIVER
+M:	Dario Binacchi <dario.binacchi@amarulasolutions.com>
+L:	linux-can@vger.kernel.org
+S:	Maintained
+F:	drivers/net/can/slcan/
+
 SLEEPABLE READ-COPY UPDATE (SRCU)
 M:	Lai Jiangshan <jiangshanlai@gmail.com>
 M:	"Paul E. McKenney" <paulmck@kernel.org>

drivers/net/can/slcan/slcan-core.c

 /*
  * slcan.c - serial line CAN interface driver (using tty line discipline)
  *
- * This file is derived from linux/drivers/net/slip/slip.c
+ * This file is derived from linux/drivers/net/slip/slip.c and got
+ * inspiration from linux/drivers/net/can/can327.c for the rework made
+ * on the line discipline code.
  *
  * slip.c Authors  : Laurence Culhane <loz@holmes.demon.co.uk>
  *                   Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
  * slcan.c Author  : Oliver Hartkopp <socketcan@hartkopp.net>
+ * can327.c Author : Max Staudt <max-linux@enpas.org>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
@@ -35,8 +38,9 @@
  *
  */
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/module.h>
-#include <linux/moduleparam.h>
 
 #include <linux/uaccess.h>
 #include <linux/bitops.h>
@@ -46,10 +50,6 @@
 #include <linux/netdevice.h>
 #include <linux/skbuff.h>
 #include <linux/rtnetlink.h>
-#include <linux/if_arp.h>
-#include <linux/if_ether.h>
-#include <linux/sched.h>
-#include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/workqueue.h>
@@ -63,30 +63,22 @@ MODULE_ALIAS_LDISC(N_SLCAN);
 MODULE_DESCRIPTION("serial line CAN interface");
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Oliver Hartkopp <socketcan@hartkopp.net>");
-
-#define SLCAN_MAGIC 0x53CA
-
-static int maxdev = 10;		/* MAX number of SLCAN channels;
-				 * This can be overridden with
-				 * insmod slcan.ko maxdev=nnn
-				 */
-module_param(maxdev, int, 0);
-MODULE_PARM_DESC(maxdev, "Maximum number of slcan interfaces");
+MODULE_AUTHOR("Dario Binacchi <dario.binacchi@amarulasolutions.com>");
 
 /* maximum rx buffer len: extended CAN frame with timestamp */
-#define SLC_MTU (sizeof("T1111222281122334455667788EA5F\r") + 1)
-
-#define SLC_CMD_LEN 1
-#define SLC_SFF_ID_LEN 3
-#define SLC_EFF_ID_LEN 8
-#define SLC_STATE_LEN 1
-#define SLC_STATE_BE_RXCNT_LEN 3
-#define SLC_STATE_BE_TXCNT_LEN 3
-#define SLC_STATE_FRAME_LEN       (1 + SLC_CMD_LEN + SLC_STATE_BE_RXCNT_LEN + \
-				   SLC_STATE_BE_TXCNT_LEN)
+#define SLCAN_MTU (sizeof("T1111222281122334455667788EA5F\r") + 1)
+
+#define SLCAN_CMD_LEN 1
+#define SLCAN_SFF_ID_LEN 3
+#define SLCAN_EFF_ID_LEN 8
+#define SLCAN_STATE_LEN 1
+#define SLCAN_STATE_BE_RXCNT_LEN 3
+#define SLCAN_STATE_BE_TXCNT_LEN 3
+#define SLCAN_STATE_FRAME_LEN       (1 + SLCAN_CMD_LEN + \
+				     SLCAN_STATE_BE_RXCNT_LEN + \
+				     SLCAN_STATE_BE_TXCNT_LEN)
 struct slcan {
 	struct can_priv         can;
-	int			magic;
 
 	/* Various fields. */
 	struct tty_struct	*tty;		/* ptr to TTY structure	     */
@@ -95,24 +87,21 @@ struct slcan {
 	struct work_struct	tx_work;	/* Flushes transmit buffer   */
 
 	/* These are pointers to the malloc()ed frame buffers. */
-	unsigned char		rbuff[SLC_MTU];	/* receiver buffer	     */
+	unsigned char		rbuff[SLCAN_MTU];	/* receiver buffer   */
 	int			rcount;         /* received chars counter    */
-	unsigned char		xbuff[SLC_MTU];	/* transmitter buffer	     */
+	unsigned char		xbuff[SLCAN_MTU];	/* transmitter buffer*/
 	unsigned char		*xhead;         /* pointer to next XMIT byte */
 	int			xleft;          /* bytes left in XMIT queue  */
 
 	unsigned long		flags;		/* Flag values/ mode etc     */
-#define SLF_INUSE		0		/* Channel in use            */
-#define SLF_ERROR		1               /* Parity, etc. error        */
-#define SLF_XCMD		2               /* Command transmission      */
+#define SLF_ERROR		0               /* Parity, etc. error        */
+#define SLF_XCMD		1               /* Command transmission      */
 	unsigned long           cmd_flags;      /* Command flags             */
 #define CF_ERR_RST		0               /* Reset errors on open      */
 	wait_queue_head_t       xcmd_wait;      /* Wait queue for commands   */
 						/* transmission              */
 };
 
-static struct net_device **slcan_devs;
-
 static const u32 slcan_bitrate_const[] = {
 	10000, 20000, 50000, 100000, 125000,
 	250000, 500000, 800000, 1000000
@@ -179,7 +168,7 @@ int slcan_enable_err_rst_on_open(struct net_device *ndev, bool on)
  *************************************************************************/
 
 /* Send one completely decapsulated can_frame to the network layer */
-static void slc_bump_frame(struct slcan *sl)
+static void slcan_bump_frame(struct slcan *sl)
 {
 	struct sk_buff *skb;
 	struct can_frame *cf;
@@ -199,10 +188,10 @@ static void slc_bump_frame(struct slcan *sl)
 		fallthrough;
 	case 't':
 		/* store dlc ASCII value and terminate SFF CAN ID string */
-		cf->len = sl->rbuff[SLC_CMD_LEN + SLC_SFF_ID_LEN];
-		sl->rbuff[SLC_CMD_LEN + SLC_SFF_ID_LEN] = 0;
+		cf->len = sl->rbuff[SLCAN_CMD_LEN + SLCAN_SFF_ID_LEN];
+		sl->rbuff[SLCAN_CMD_LEN + SLCAN_SFF_ID_LEN] = 0;
 		/* point to payload data behind the dlc */
-		cmd += SLC_CMD_LEN + SLC_SFF_ID_LEN + 1;
+		cmd += SLCAN_CMD_LEN + SLCAN_SFF_ID_LEN + 1;
 		break;
 	case 'R':
 		cf->can_id = CAN_RTR_FLAG;
@@ -210,16 +199,16 @@ static void slc_bump_frame(struct slcan *sl)
 	case 'T':
 		cf->can_id |= CAN_EFF_FLAG;
 		/* store dlc ASCII value and terminate EFF CAN ID string */
-		cf->len = sl->rbuff[SLC_CMD_LEN + SLC_EFF_ID_LEN];
-		sl->rbuff[SLC_CMD_LEN + SLC_EFF_ID_LEN] = 0;
+		cf->len = sl->rbuff[SLCAN_CMD_LEN + SLCAN_EFF_ID_LEN];
+		sl->rbuff[SLCAN_CMD_LEN + SLCAN_EFF_ID_LEN] = 0;
 		/* point to payload data behind the dlc */
-		cmd += SLC_CMD_LEN + SLC_EFF_ID_LEN + 1;
+		cmd += SLCAN_CMD_LEN + SLCAN_EFF_ID_LEN + 1;
 		break;
 	default:
 		goto decode_failed;
 	}
 
-	if (kstrtou32(sl->rbuff + SLC_CMD_LEN, 16, &tmpid))
+	if (kstrtou32(sl->rbuff + SLCAN_CMD_LEN, 16, &tmpid))
 		goto decode_failed;
 
 	cf->can_id |= tmpid;
@@ -266,7 +255,7 @@ static void slc_bump_frame(struct slcan *sl)
  * sb256256 : state bus-off: rx counter 256, tx counter 256
  * sa057033 : state active, rx counter 57, tx counter 33
  */
-static void slc_bump_state(struct slcan *sl)
+static void slcan_bump_state(struct slcan *sl)
 {
 	struct net_device *dev = sl->dev;
 	struct sk_buff *skb;
@@ -292,16 +281,16 @@ static void slc_bump_state(struct slcan *sl)
 		return;
 	}
 
-	if (state == sl->can.state || sl->rcount < SLC_STATE_FRAME_LEN)
+	if (state == sl->can.state || sl->rcount < SLCAN_STATE_FRAME_LEN)
 		return;
 
-	cmd += SLC_STATE_BE_RXCNT_LEN + SLC_CMD_LEN + 1;
-	cmd[SLC_STATE_BE_TXCNT_LEN] = 0;
+	cmd += SLCAN_STATE_BE_RXCNT_LEN + SLCAN_CMD_LEN + 1;
+	cmd[SLCAN_STATE_BE_TXCNT_LEN] = 0;
 	if (kstrtou32(cmd, 10, &txerr))
 		return;
 
 	*cmd = 0;
-	cmd -= SLC_STATE_BE_RXCNT_LEN;
+	cmd -= SLCAN_STATE_BE_RXCNT_LEN;
 	if (kstrtou32(cmd, 10, &rxerr))
 		return;
 
@@ -330,7 +319,7 @@ static void slc_bump_state(struct slcan *sl)
  * e1a : len 1, errors: ACK error
  * e3bcO: len 3, errors: Bit0 error, CRC error, Tx overrun error
  */
-static void slc_bump_err(struct slcan *sl)
+static void slcan_bump_err(struct slcan *sl)
 {
 	struct net_device *dev = sl->dev;
 	struct sk_buff *skb;
@@ -346,7 +335,7 @@ static void slc_bump_err(struct slcan *sl)
 	else
 		return;
 
-	if ((len + SLC_CMD_LEN + 1) > sl->rcount)
+	if ((len + SLCAN_CMD_LEN + 1) > sl->rcount)
 		return;
 
 	skb = alloc_can_err_skb(dev, &cf);
@@ -354,7 +343,7 @@ static void slc_bump_err(struct slcan *sl)
 	if (skb)
 		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
 
-	cmd += SLC_CMD_LEN + 1;
+	cmd += SLCAN_CMD_LEN + 1;
 	for (i = 0; i < len; i++, cmd++) {
 		switch (*cmd) {
 		case 'a':
@@ -443,7 +432,7 @@ static void slc_bump_err(struct slcan *sl)
 		netif_rx(skb);
 }
 
-static void slc_bump(struct slcan *sl)
+static void slcan_bump(struct slcan *sl)
 {
 	switch (sl->rbuff[0]) {
 	case 'r':
@@ -453,11 +442,11 @@ static void slc_bump(struct slcan *sl)
 	case 'R':
 		fallthrough;
 	case 'T':
-		return slc_bump_frame(sl);
+		return slcan_bump_frame(sl);
 	case 'e':
-		return slc_bump_err(sl);
+		return slcan_bump_err(sl);
 	case 's':
-		return slc_bump_state(sl);
+		return slcan_bump_state(sl);
 	default:
 		return;
 	}
@@ -469,12 +458,12 @@ static void slcan_unesc(struct slcan *sl, unsigned char s)
 	if ((s == '\r') || (s == '\a')) { /* CR or BEL ends the pdu */
 		if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
 		    sl->rcount > 4)
-			slc_bump(sl);
+			slcan_bump(sl);
 
 		sl->rcount = 0;
 	} else {
 		if (!test_bit(SLF_ERROR, &sl->flags))  {
-			if (sl->rcount < SLC_MTU)  {
+			if (sl->rcount < SLCAN_MTU)  {
 				sl->rbuff[sl->rcount++] = s;
 				return;
 			}
@@ -490,7 +479,7 @@ static void slcan_unesc(struct slcan *sl, unsigned char s)
  *************************************************************************/
 
 /* Encapsulate one can_frame and stuff into a TTY queue. */
-static void slc_encaps(struct slcan *sl, struct can_frame *cf)
+static void slcan_encaps(struct slcan *sl, struct can_frame *cf)
 {
 	int actual, i;
 	unsigned char *pos;
@@ -507,11 +496,11 @@ static void slc_encaps(struct slcan *sl, struct can_frame *cf)
 	/* determine number of chars for the CAN-identifier */
 	if (cf->can_id & CAN_EFF_FLAG) {
 		id &= CAN_EFF_MASK;
-		endpos = pos + SLC_EFF_ID_LEN;
+		endpos = pos + SLCAN_EFF_ID_LEN;
 	} else {
 		*pos |= 0x20; /* convert R/T to lower case for SFF */
 		id &= CAN_SFF_MASK;
-		endpos = pos + SLC_SFF_ID_LEN;
+		endpos = pos + SLCAN_SFF_ID_LEN;
 	}
 
 	/* build 3 (SFF) or 8 (EFF) digit CAN identifier */
@@ -521,7 +510,8 @@ static void slc_encaps(struct slcan *sl, struct can_frame *cf)
 		id >>= 4;
 	}
 
-	pos += (cf->can_id & CAN_EFF_FLAG) ? SLC_EFF_ID_LEN : SLC_SFF_ID_LEN;
+	pos += (cf->can_id & CAN_EFF_FLAG) ?
+		SLCAN_EFF_ID_LEN : SLCAN_SFF_ID_LEN;
 
 	*pos++ = cf->len + '0';
 
@@ -557,9 +547,8 @@ static void slcan_transmit(struct work_struct *work)
 
 	spin_lock_bh(&sl->lock);
 	/* First make sure we're connected. */
-	if (!sl->tty || sl->magic != SLCAN_MAGIC ||
-	    (unlikely(!netif_running(sl->dev)) &&
-	     likely(!test_bit(SLF_XCMD, &sl->flags)))) {
+	if (unlikely(!netif_running(sl->dev)) &&
+	    likely(!test_bit(SLF_XCMD, &sl->flags))) {
 		spin_unlock_bh(&sl->lock);
 		return;
 	}
@@ -594,17 +583,14 @@ static void slcan_transmit(struct work_struct *work)
  */
 static void slcan_write_wakeup(struct tty_struct *tty)
 {
-	struct slcan *sl;
+	struct slcan *sl = (struct slcan *)tty->disc_data;
 
-	rcu_read_lock();
-	sl = rcu_dereference(tty->disc_data);
-	if (sl)
-		schedule_work(&sl->tx_work);
-	rcu_read_unlock();
+	schedule_work(&sl->tx_work);
 }
 
 /* Send a can_frame to a TTY queue. */
-static netdev_tx_t slc_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t slcan_netdev_xmit(struct sk_buff *skb,
+				     struct net_device *dev)
 {
 	struct slcan *sl = netdev_priv(dev);
 
@@ -623,7 +609,7 @@ static netdev_tx_t slc_xmit(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	netif_stop_queue(sl->dev);
-	slc_encaps(sl, (struct can_frame *)skb->data); /* encaps & send */
+	slcan_encaps(sl, (struct can_frame *)skb->data); /* encaps & send */
 	spin_unlock(&sl->lock);
 
 out:
@@ -666,30 +652,26 @@ static int slcan_transmit_cmd(struct slcan *sl, const unsigned char *cmd)
 }
 
 /* Netdevice UP -> DOWN routine */
-static int slc_close(struct net_device *dev)
+static int slcan_netdev_close(struct net_device *dev)
 {
 	struct slcan *sl = netdev_priv(dev);
 	int err;
 
-	spin_lock_bh(&sl->lock);
-	if (sl->tty) {
-		if (sl->can.bittiming.bitrate &&
-		    sl->can.bittiming.bitrate != CAN_BITRATE_UNKNOWN) {
-			spin_unlock_bh(&sl->lock);
-			err = slcan_transmit_cmd(sl, "C\r");
-			spin_lock_bh(&sl->lock);
-			if (err)
-				netdev_warn(dev,
-					    "failed to send close command 'C\\r'\n");
-		}
-
-		/* TTY discipline is running. */
-		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+	if (sl->can.bittiming.bitrate &&
+	    sl->can.bittiming.bitrate != CAN_BITRATE_UNKNOWN) {
+		err = slcan_transmit_cmd(sl, "C\r");
+		if (err)
+			netdev_warn(dev,
+				    "failed to send close command 'C\\r'\n");
 	}
+
+	/* TTY discipline is running. */
+	clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+	flush_work(&sl->tx_work);
+
 	netif_stop_queue(dev);
 	sl->rcount   = 0;
 	sl->xleft    = 0;
-	spin_unlock_bh(&sl->lock);
 	close_candev(dev);
 	sl->can.state = CAN_STATE_STOPPED;
 	if (sl->can.bittiming.bitrate == CAN_BITRATE_UNKNOWN)
@@ -699,15 +681,12 @@ static int slc_close(struct net_device *dev)
 }
 
 /* Netdevice DOWN -> UP routine */
-static int slc_open(struct net_device *dev)
+static int slcan_netdev_open(struct net_device *dev)
 {
 	struct slcan *sl = netdev_priv(dev);
-	unsigned char cmd[SLC_MTU];
+	unsigned char cmd[SLCAN_MTU];
 	int err, s;
 
-	if (!sl->tty)
-		return -ENODEV;
-
 	/* The baud rate is not set with the command
 	 * `ip link set <iface> type can bitrate <baud>' and therefore
 	 * can.bittiming.bitrate is CAN_BITRATE_UNSET (0), causing
@@ -722,8 +701,6 @@ static int slc_open(struct net_device *dev)
 		return err;
 	}
 
-	sl->flags &= BIT(SLF_INUSE);
-
 	if (sl->can.bittiming.bitrate != CAN_BITRATE_UNKNOWN) {
 		for (s = 0; s < ARRAY_SIZE(slcan_bitrate_const); s++) {
 			if (sl->can.bittiming.bitrate == slcan_bitrate_const[s])
@@ -751,10 +728,20 @@ static int slc_open(struct net_device *dev)
 			}
 		}
 
-		err = slcan_transmit_cmd(sl, "O\r");
-		if (err) {
-			netdev_err(dev, "failed to send open command 'O\\r'\n");
-			goto cmd_transmit_failed;
+		if (sl->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
+			err = slcan_transmit_cmd(sl, "L\r");
+			if (err) {
+				netdev_err(dev,
+					   "failed to send listen-only command 'L\\r'\n");
+				goto cmd_transmit_failed;
+			}
+		} else {
+			err = slcan_transmit_cmd(sl, "O\r");
+			if (err) {
+				netdev_err(dev,
+					   "failed to send open command 'O\\r'\n");
+				goto cmd_transmit_failed;
+			}
 		}
 	}
 
@@ -767,24 +754,11 @@ static int slc_open(struct net_device *dev)
 	return err;
 }
 
-static void slc_dealloc(struct slcan *sl)
-{
-	int i = sl->dev->base_addr;
-
-	free_candev(sl->dev);
-	slcan_devs[i] = NULL;
-}
-
-static int slcan_change_mtu(struct net_device *dev, int new_mtu)
-{
-	return -EINVAL;
-}
-
-static const struct net_device_ops slc_netdev_ops = {
-	.ndo_open               = slc_open,
-	.ndo_stop               = slc_close,
-	.ndo_start_xmit         = slc_xmit,
-	.ndo_change_mtu         = slcan_change_mtu,
+static const struct net_device_ops slcan_netdev_ops = {
+	.ndo_open               = slcan_netdev_open,
+	.ndo_stop               = slcan_netdev_close,
+	.ndo_start_xmit         = slcan_netdev_xmit,
+	.ndo_change_mtu         = can_change_mtu,
 };
 
 /******************************************
@@ -804,7 +778,7 @@ static void slcan_receive_buf(struct tty_struct *tty,
 {
 	struct slcan *sl = (struct slcan *)tty->disc_data;
 
-	if (!sl || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev))
+	if (!netif_running(sl->dev))
 		return;
 
 	/* Read the characters out of the buffer */
@@ -819,80 +793,15 @@ static void slcan_receive_buf(struct tty_struct *tty,
 	}
 }
 
-/************************************
- *  slcan_open helper routines.
- ************************************/
-
-/* Collect hanged up channels */
-static void slc_sync(void)
-{
-	int i;
-	struct net_device *dev;
-	struct slcan	  *sl;
-
-	for (i = 0; i < maxdev; i++) {
-		dev = slcan_devs[i];
-		if (!dev)
-			break;
-
-		sl = netdev_priv(dev);
-		if (sl->tty)
-			continue;
-		if (dev->flags & IFF_UP)
-			dev_close(dev);
-	}
-}
-
-/* Find a free SLCAN channel, and link in this `tty' line. */
-static struct slcan *slc_alloc(void)
-{
-	int i;
-	struct net_device *dev = NULL;
-	struct slcan       *sl;
-
-	for (i = 0; i < maxdev; i++) {
-		dev = slcan_devs[i];
-		if (!dev)
-			break;
-	}
-
-	/* Sorry, too many, all slots in use */
-	if (i >= maxdev)
-		return NULL;
-
-	dev = alloc_candev(sizeof(*sl), 1);
-	if (!dev)
-		return NULL;
-
-	snprintf(dev->name, sizeof(dev->name), "slcan%d", i);
-	dev->netdev_ops = &slc_netdev_ops;
-	dev->ethtool_ops = &slcan_ethtool_ops;
-	dev->base_addr  = i;
-	sl = netdev_priv(dev);
-
-	/* Initialize channel control data */
-	sl->magic = SLCAN_MAGIC;
-	sl->dev	= dev;
-	sl->can.bitrate_const = slcan_bitrate_const;
-	sl->can.bitrate_const_cnt = ARRAY_SIZE(slcan_bitrate_const);
-	spin_lock_init(&sl->lock);
-	INIT_WORK(&sl->tx_work, slcan_transmit);
-	init_waitqueue_head(&sl->xcmd_wait);
-	slcan_devs[i] = dev;
-
-	return sl;
-}
-
 /* Open the high-level part of the SLCAN channel.
  * This function is called by the TTY module when the
- * SLCAN line discipline is called for.  Because we are
- * sure the tty line exists, we only have to link it to
- * a free SLCAN channel...
+ * SLCAN line discipline is called for.
  *
  * Called in process context serialized from other ldisc calls.
  */
 static int slcan_open(struct tty_struct *tty)
 {
+	struct net_device *dev;
 	struct slcan *sl;
 	int err;
 
@@ -902,72 +811,50 @@ static int slcan_open(struct tty_struct *tty)
 	if (!tty->ops->write)
 		return -EOPNOTSUPP;
 
-	/* RTnetlink lock is misused here to serialize concurrent
-	 * opens of slcan channels. There are better ways, but it is
-	 * the simplest one.
-	 */
-	rtnl_lock();
+	dev = alloc_candev(sizeof(*sl), 1);
+	if (!dev)
+		return -ENFILE;
 
-	/* Collect hanged up channels. */
-	slc_sync();
+	sl = netdev_priv(dev);
 
-	sl = tty->disc_data;
+	/* Configure TTY interface */
+	tty->receive_room = 65536; /* We don't flow control */
+	sl->rcount = 0;
+	sl->xleft = 0;
+	spin_lock_init(&sl->lock);
+	INIT_WORK(&sl->tx_work, slcan_transmit);
+	init_waitqueue_head(&sl->xcmd_wait);
 
-	err = -EEXIST;
-	/* First make sure we're not already connected. */
-	if (sl && sl->magic == SLCAN_MAGIC)
-		goto err_exit;
+	/* Configure CAN metadata */
+	sl->can.bitrate_const = slcan_bitrate_const;
+	sl->can.bitrate_const_cnt = ARRAY_SIZE(slcan_bitrate_const);
+	sl->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
 
-	/* OK.  Find a free SLCAN channel to use. */
-	err = -ENFILE;
-	sl = slc_alloc();
-	if (!sl)
-		goto err_exit;
+	/* Configure netdev interface */
+	sl->dev	= dev;
+	dev->netdev_ops = &slcan_netdev_ops;
+	dev->ethtool_ops = &slcan_ethtool_ops;
 
+	/* Mark ldisc channel as alive */
 	sl->tty = tty;
 	tty->disc_data = sl;
 
-	if (!test_bit(SLF_INUSE, &sl->flags)) {
-		/* Perform the low-level SLCAN initialization. */
-		sl->rcount   = 0;
-		sl->xleft    = 0;
-
-		set_bit(SLF_INUSE, &sl->flags);
-
-		rtnl_unlock();
-		err = register_candev(sl->dev);
-		if (err) {
-			pr_err("slcan: can't register candev\n");
-			goto err_free_chan;
-		}
-	} else {
-		rtnl_unlock();
+	err = register_candev(dev);
+	if (err) {
+		free_candev(dev);
+		pr_err("can't register candev\n");
+		return err;
 	}
 
-	tty->receive_room = 65536;	/* We don't flow control */
-
+	netdev_info(dev, "slcan on %s.\n", tty->name);
 	/* TTY layer expects 0 on success */
 	return 0;
-
-err_free_chan:
-	rtnl_lock();
-	sl->tty = NULL;
-	tty->disc_data = NULL;
-	clear_bit(SLF_INUSE, &sl->flags);
-	slc_dealloc(sl);
-	rtnl_unlock();
-	return err;
-
-err_exit:
-	rtnl_unlock();
-
-	/* Count references from TTY module */
-	return err;
 }
 
 /* Close down a SLCAN channel.
  * This means flushing out any pending queues, and then returning. This
  * call is serialized against other ldisc functions.
+ * Once this is called, no other ldisc function of ours is entered.
  *
  * We also use this method for a hangup event.
  */
@@ -975,28 +862,20 @@ static void slcan_close(struct tty_struct *tty)
 {
 	struct slcan *sl = (struct slcan *)tty->disc_data;
 
-	/* First make sure we're connected. */
-	if (!sl || sl->magic != SLCAN_MAGIC || sl->tty != tty)
-		return;
+	/* unregister_netdev() calls .ndo_stop() so we don't have to.
+	 * Our .ndo_stop() also flushes the TTY write wakeup handler,
+	 * so we can safely set sl->tty = NULL after this.
+	 */
+	unregister_candev(sl->dev);
 
+	/* Mark channel as dead */
 	spin_lock_bh(&sl->lock);
-	rcu_assign_pointer(tty->disc_data, NULL);
+	tty->disc_data = NULL;
 	sl->tty = NULL;
 	spin_unlock_bh(&sl->lock);
 
-	synchronize_rcu();
-	flush_work(&sl->tx_work);
-
-	slc_close(sl->dev);
-	unregister_candev(sl->dev);
-	rtnl_lock();
-	slc_dealloc(sl);
-	rtnl_unlock();
-}
-
-static void slcan_hangup(struct tty_struct *tty)
-{
-	slcan_close(tty);
+	netdev_info(sl->dev, "slcan off %s.\n", tty->name);
+	free_candev(sl->dev);
 }
 
 /* Perform I/O control on an active SLCAN channel. */
@@ -1006,10 +885,6 @@ static int slcan_ioctl(struct tty_struct *tty, unsigned int cmd,
 	struct slcan *sl = (struct slcan *)tty->disc_data;
 	unsigned int tmp;
 
-	/* First make sure we're connected. */
-	if (!sl || sl->magic != SLCAN_MAGIC)
-		return -EINVAL;
-
 	switch (cmd) {
 	case SIOCGIFNAME:
 		tmp = strlen(sl->dev->name) + 1;
@@ -1025,13 +900,12 @@ static int slcan_ioctl(struct tty_struct *tty, unsigned int cmd,
 	}
 }
 
-static struct tty_ldisc_ops slc_ldisc = {
+static struct tty_ldisc_ops slcan_ldisc = {
 	.owner		= THIS_MODULE,
 	.num		= N_SLCAN,
-	.name		= "slcan",
+	.name		= KBUILD_MODNAME,
 	.open		= slcan_open,
 	.close		= slcan_close,
-	.hangup		= slcan_hangup,
 	.ioctl		= slcan_ioctl,
 	.receive_buf	= slcan_receive_buf,
 	.write_wakeup	= slcan_write_wakeup,
@@ -1041,79 +915,22 @@ static int __init slcan_init(void)
 {
 	int status;
 
-	if (maxdev < 4)
-		maxdev = 4; /* Sanity */
-
-	pr_info("slcan: serial line CAN interface driver\n");
-	pr_info("slcan: %d dynamic interface channels.\n", maxdev);
-
-	slcan_devs = kcalloc(maxdev, sizeof(struct net_device *), GFP_KERNEL);
-	if (!slcan_devs)
-		return -ENOMEM;
+	pr_info("serial line CAN interface driver\n");
 
 	/* Fill in our line protocol discipline, and register it */
-	status = tty_register_ldisc(&slc_ldisc);
-	if (status)  {
-		pr_err("slcan: can't register line discipline\n");
-		kfree(slcan_devs);
-	}
+	status = tty_register_ldisc(&slcan_ldisc);
+	if (status)
+		pr_err("can't register line discipline\n");
+
 	return status;
 }
 
 static void __exit slcan_exit(void)
 {
-	int i;
-	struct net_device *dev;
-	struct slcan *sl;
-	unsigned long timeout = jiffies + HZ;
-	int busy = 0;
-
-	if (!slcan_devs)
-		return;
-
-	/* First of all: check for active disciplines and hangup them.
-	 */
-	do {
-		if (busy)
-			msleep_interruptible(100);
-
-		busy = 0;
-		for (i = 0; i < maxdev; i++) {
-			dev = slcan_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
+	/* This will only be called when all channels have been closed by
+	 * userspace - tty_ldisc.c takes care of the module's refcount.
 	 */
-
-	for (i = 0; i < maxdev; i++) {
-		dev = slcan_devs[i];
-		if (!dev)
-			continue;
-
-		sl = netdev_priv(dev);
-		if (sl->tty)
-			netdev_err(dev, "tty discipline still running\n");
-
-		slc_close(dev);
-		unregister_candev(dev);
-		slc_dealloc(sl);
-	}
-
-	kfree(slcan_devs);
-	slcan_devs = NULL;
-
-	tty_unregister_ldisc(&slc_ldisc);
+	tty_unregister_ldisc(&slcan_ldisc);
 }
 
 module_init(slcan_init);