can: slcan: move driver into separate sub directory

This patch moves the slcan driver into a separate directory, a later
patch will add more files.

Link: https://lore.kernel.org/all/20220628163137.413025-10-dario.binacchi@amarulasolutions.com
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 885 insertions, 0 deletions

diff --git a/drivers/net/can/slcan/slcan-core.c b/drivers/net/can/slcan/slcan-core.c
new file mode 100644
index 000000000000..249b5ade06fc
--- /dev/null
+++ b/drivers/net/can/slcan/slcan-core.c
@@ -0,0 +1,885 @@
+/*
+ * slcan.c - serial line CAN interface driver (using tty line discipline)
+ *
+ * This file is derived from linux/drivers/net/slip/slip.c
+ *
+ * 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>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, see http://www.gnu.org/licenses/gpl.html
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+
+#include <linux/uaccess.h>
+#include <linux/bitops.h>
+#include <linux/string.h>
+#include <linux/tty.h>
+#include <linux/errno.h>
+#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>
+#include <linux/can.h>
+#include <linux/can/dev.h>
+#include <linux/can/skb.h>
+
+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");
+
+/* 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
+
+struct slcan {
+	struct can_priv         can;
+	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   */
+
+	/* These are pointers to the malloc()ed frame buffers. */
+	unsigned char		rbuff[SLC_MTU];	/* receiver buffer	     */
+	int			rcount;         /* received chars counter    */
+	unsigned char		xbuff[SLC_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      */
+	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
+};
+
+ /************************************************************************
+  *			SLCAN ENCAPSULATION FORMAT			 *
+  ************************************************************************/
+
+/*
+ * A CAN frame has a can_id (11 bit standard frame format OR 29 bit extended
+ * frame format) a data length code (len) which can be from 0 to 8
+ * and up to <len> data bytes as payload.
+ * Additionally a CAN frame may become a remote transmission frame if the
+ * RTR-bit is set. This causes another ECU to send a CAN frame with the
+ * given can_id.
+ *
+ * The SLCAN ASCII representation of these different frame types is:
+ * <type> <id> <dlc> <data>*
+ *
+ * Extended frames (29 bit) are defined by capital characters in the type.
+ * RTR frames are defined as 'r' types - normal frames have 't' type:
+ * t => 11 bit data frame
+ * r => 11 bit RTR frame
+ * T => 29 bit data frame
+ * R => 29 bit RTR frame
+ *
+ * The <id> is 3 (standard) or 8 (extended) bytes in ASCII Hex (base64).
+ * The <dlc> is a one byte ASCII number ('0' - '8')
+ * The <data> section has at much ASCII Hex bytes as defined by the <dlc>
+ *
+ * Examples:
+ *
+ * t1230 : can_id 0x123, len 0, no data
+ * t4563112233 : can_id 0x456, len 3, data 0x11 0x22 0x33
+ * T12ABCDEF2AA55 : extended can_id 0x12ABCDEF, len 2, data 0xAA 0x55
+ * r1230 : can_id 0x123, len 0, no data, remote transmission request
+ *
+ */
+
+ /************************************************************************
+  *			STANDARD SLCAN DECAPSULATION			 *
+  ************************************************************************/
+
+/* Send one completely decapsulated can_frame to the network layer */
+static void slc_bump(struct slcan *sl)
+{
+	struct sk_buff *skb;
+	struct can_frame *cf;
+	int i, tmp;
+	u32 tmpid;
+	char *cmd = sl->rbuff;
+
+	skb = alloc_can_skb(sl->dev, &cf);
+	if (unlikely(!skb)) {
+		sl->dev->stats.rx_dropped++;
+		return;
+	}
+
+	switch (*cmd) {
+	case 'r':
+		cf->can_id = CAN_RTR_FLAG;
+		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;
+		/* point to payload data behind the dlc */
+		cmd += SLC_CMD_LEN + SLC_SFF_ID_LEN + 1;
+		break;
+	case 'R':
+		cf->can_id = CAN_RTR_FLAG;
+		fallthrough;
+	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;
+		/* point to payload data behind the dlc */
+		cmd += SLC_CMD_LEN + SLC_EFF_ID_LEN + 1;
+		break;
+	default:
+		goto decode_failed;
+	}
+
+	if (kstrtou32(sl->rbuff + SLC_CMD_LEN, 16, &tmpid))
+		goto decode_failed;
+
+	cf->can_id |= tmpid;
+
+	/* get len from sanitized ASCII value */
+	if (cf->len >= '0' && cf->len < '9')
+		cf->len -= '0';
+	else
+		goto decode_failed;
+
+	/* RTR frames may have a dlc > 0 but they never have any data bytes */
+	if (!(cf->can_id & CAN_RTR_FLAG)) {
+		for (i = 0; i < cf->len; i++) {
+			tmp = hex_to_bin(*cmd++);
+			if (tmp < 0)
+				goto decode_failed;
+
+			cf->data[i] = (tmp << 4);
+			tmp = hex_to_bin(*cmd++);
+			if (tmp < 0)
+				goto decode_failed;
+
+			cf->data[i] |= tmp;
+		}
+	}
+
+	sl->dev->stats.rx_packets++;
+	if (!(cf->can_id & CAN_RTR_FLAG))
+		sl->dev->stats.rx_bytes += cf->len;
+
+	netif_rx(skb);
+	return;
+
+decode_failed:
+	sl->dev->stats.rx_errors++;
+	dev_kfree_skb(skb);
+}
+
+/* parse tty input stream */
+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);
+		}
+		sl->rcount = 0;
+	} else {
+		if (!test_bit(SLF_ERROR, &sl->flags))  {
+			if (sl->rcount < SLC_MTU)  {
+				sl->rbuff[sl->rcount++] = s;
+				return;
+			} else {
+				sl->dev->stats.rx_over_errors++;
+				set_bit(SLF_ERROR, &sl->flags);
+			}
+		}
+	}
+}
+
+ /************************************************************************
+  *			STANDARD SLCAN ENCAPSULATION			 *
+  ************************************************************************/
+
+/* Encapsulate one can_frame and stuff into a TTY queue. */
+static void slc_encaps(struct slcan *sl, struct can_frame *cf)
+{
+	int actual, i;
+	unsigned char *pos;
+	unsigned char *endpos;
+	canid_t id = cf->can_id;
+
+	pos = sl->xbuff;
+
+	if (cf->can_id & CAN_RTR_FLAG)
+		*pos = 'R'; /* becomes 'r' in standard frame format (SFF) */
+	else
+		*pos = 'T'; /* becomes 't' in standard frame format (SSF) */
+
+	/* 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;
+	} else {
+		*pos |= 0x20; /* convert R/T to lower case for SFF */
+		id &= CAN_SFF_MASK;
+		endpos = pos + SLC_SFF_ID_LEN;
+	}
+
+	/* build 3 (SFF) or 8 (EFF) digit CAN identifier */
+	pos++;
+	while (endpos >= pos) {
+		*endpos-- = hex_asc_upper[id & 0xf];
+		id >>= 4;
+	}
+
+	pos += (cf->can_id & CAN_EFF_FLAG) ? SLC_EFF_ID_LEN : SLC_SFF_ID_LEN;
+
+	*pos++ = cf->len + '0';
+
+	/* RTR frames may have a dlc > 0 but they never have any data bytes */
+	if (!(cf->can_id & CAN_RTR_FLAG)) {
+		for (i = 0; i < cf->len; i++)
+			pos = hex_byte_pack_upper(pos, cf->data[i]);
+
+		sl->dev->stats.tx_bytes += cf->len;
+	}
+
+	*pos++ = '\r';
+
+	/* 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, pos - sl->xbuff);
+	sl->xleft = (pos - sl->xbuff) - actual;
+	sl->xhead = sl->xbuff + actual;
+}
+
+/* Write out any remaining transmit buffer. Scheduled when tty is writable */
+static void slcan_transmit(struct work_struct *work)
+{
+	struct slcan *sl = container_of(work, struct slcan, tx_work);
+	int actual;
+
+	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)))) {
+		spin_unlock_bh(&sl->lock);
+		return;
+	}
+
+	if (sl->xleft <= 0)  {
+		if (unlikely(test_bit(SLF_XCMD, &sl->flags))) {
+			clear_bit(SLF_XCMD, &sl->flags);
+			clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+			spin_unlock_bh(&sl->lock);
+			wake_up(&sl->xcmd_wait);
+			return;
+		}
+
+		/* 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);
+		netif_wake_queue(sl->dev);
+		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 slcan_write_wakeup(struct tty_struct *tty)
+{
+	struct slcan *sl;
+
+	rcu_read_lock();
+	sl = rcu_dereference(tty->disc_data);
+	if (sl)
+		schedule_work(&sl->tx_work);
+	rcu_read_unlock();
+}
+
+/* Send a can_frame to a TTY queue. */
+static netdev_tx_t slc_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct slcan *sl = netdev_priv(dev);
+
+	if (can_dropped_invalid_skb(dev, skb))
+		return NETDEV_TX_OK;
+
+	spin_lock(&sl->lock);
+	if (!netif_running(dev))  {
+		spin_unlock(&sl->lock);
+		netdev_warn(dev, "xmit: iface is down\n");
+		goto out;
+	}
+	if (sl->tty == NULL) {
+		spin_unlock(&sl->lock);
+		goto out;
+	}
+
+	netif_stop_queue(sl->dev);
+	slc_encaps(sl, (struct can_frame *) skb->data); /* encaps & send */
+	spin_unlock(&sl->lock);
+
+out:
+	kfree_skb(skb);
+	return NETDEV_TX_OK;
+}
+
+
+/******************************************
+ *   Routines looking at netdevice side.
+ ******************************************/
+
+static int slcan_transmit_cmd(struct slcan *sl, const unsigned char *cmd)
+{
+	int ret, actual, n;
+
+	spin_lock(&sl->lock);
+	if (!sl->tty) {
+		spin_unlock(&sl->lock);
+		return -ENODEV;
+	}
+
+	n = snprintf(sl->xbuff, sizeof(sl->xbuff), "%s", cmd);
+	set_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+	actual = sl->tty->ops->write(sl->tty, sl->xbuff, n);
+	sl->xleft = n - actual;
+	sl->xhead = sl->xbuff + actual;
+	set_bit(SLF_XCMD, &sl->flags);
+	spin_unlock(&sl->lock);
+	ret = wait_event_interruptible_timeout(sl->xcmd_wait,
+					       !test_bit(SLF_XCMD, &sl->flags),
+					       HZ);
+	clear_bit(SLF_XCMD, &sl->flags);
+	if (ret == -ERESTARTSYS)
+		return ret;
+
+	if (ret == 0)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+/* Netdevice UP -> DOWN routine */
+static int slc_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);
+	}
+	netif_stop_queue(dev);
+	close_candev(dev);
+	sl->can.state = CAN_STATE_STOPPED;
+	if (sl->can.bittiming.bitrate == CAN_BITRATE_UNKNOWN)
+		sl->can.bittiming.bitrate = CAN_BITRATE_UNSET;
+
+	sl->rcount   = 0;
+	sl->xleft    = 0;
+	spin_unlock_bh(&sl->lock);
+
+	return 0;
+}
+
+/* Netdevice DOWN -> UP routine */
+static int slc_open(struct net_device *dev)
+{
+	struct slcan *sl = netdev_priv(dev);
+	unsigned char cmd[SLC_MTU];
+	int err, s;
+
+	if (sl->tty == NULL)
+		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
+	 * open_candev() to fail. So let's set to a fake value.
+	 */
+	if (sl->can.bittiming.bitrate == CAN_BITRATE_UNSET)
+		sl->can.bittiming.bitrate = CAN_BITRATE_UNKNOWN;
+
+	err = open_candev(dev);
+	if (err) {
+		netdev_err(dev, "failed to open can device\n");
+		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])
+				break;
+		}
+
+		/* The CAN framework has already validate the bitrate value,
+		 * so we can avoid to check if `s' has been properly set.
+		 */
+
+		snprintf(cmd, sizeof(cmd), "C\rS%d\r", s);
+		err = slcan_transmit_cmd(sl, cmd);
+		if (err) {
+			netdev_err(dev,
+				   "failed to send bitrate command 'C\\rS%d\\r'\n",
+				   s);
+			goto cmd_transmit_failed;
+		}
+
+		err = slcan_transmit_cmd(sl, "O\r");
+		if (err) {
+			netdev_err(dev, "failed to send open command 'O\\r'\n");
+			goto cmd_transmit_failed;
+		}
+	}
+
+	sl->can.state = CAN_STATE_ERROR_ACTIVE;
+	netif_start_queue(dev);
+	return 0;
+
+cmd_transmit_failed:
+	close_candev(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,
+};
+
+/******************************************
+  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 SLCAN 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 slcan_receive_buf(struct tty_struct *tty,
+			      const unsigned char *cp, const char *fp,
+			      int count)
+{
+	struct slcan *sl = (struct slcan *) tty->disc_data;
+
+	if (!sl || sl->magic != SLCAN_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;
+		}
+		slcan_unesc(sl, *cp++);
+	}
+}
+
+/************************************
+ *  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 == NULL)
+			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 == NULL)
+			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->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...
+ *
+ * Called in process context serialized from other ldisc calls.
+ */
+
+static int slcan_open(struct tty_struct *tty)
+{
+	struct slcan *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 slcan channels. There are better ways, but it is
+	   the simplest one.
+	 */
+	rtnl_lock();
+
+	/* Collect hanged up channels. */
+	slc_sync();
+
+	sl = tty->disc_data;
+
+	err = -EEXIST;
+	/* First make sure we're not already connected. */
+	if (sl && sl->magic == SLCAN_MAGIC)
+		goto err_exit;
+
+	/* OK.  Find a free SLCAN channel to use. */
+	err = -ENFILE;
+	sl = slc_alloc();
+	if (sl == NULL)
+		goto err_exit;
+
+	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();
+	}
+
+	tty->receive_room = 65536;	/* We don't flow control */
+
+	/* 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.
+ *
+ * We also use this method for a hangup event.
+ */
+
+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;
+
+	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);
+
+	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);
+}
+
+/* Perform I/O control on an active SLCAN channel. */
+static int slcan_ioctl(struct tty_struct *tty, unsigned int cmd,
+		       unsigned long arg)
+{
+	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;
+		if (copy_to_user((void __user *)arg, sl->dev->name, tmp))
+			return -EFAULT;
+		return 0;
+
+	case SIOCSIFHWADDR:
+		return -EINVAL;
+
+	default:
+		return tty_mode_ioctl(tty, cmd, arg);
+	}
+}
+
+static struct tty_ldisc_ops slc_ldisc = {
+	.owner		= THIS_MODULE,
+	.num		= N_SLCAN,
+	.name		= "slcan",
+	.open		= slcan_open,
+	.close		= slcan_close,
+	.hangup		= slcan_hangup,
+	.ioctl		= slcan_ioctl,
+	.receive_buf	= slcan_receive_buf,
+	.write_wakeup	= slcan_write_wakeup,
+};
+
+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;
+
+	/* Fill in our line protocol discipline, and register it */
+	status = tty_register_ldisc(&slc_ldisc);
+	if (status)  {
+		printk(KERN_ERR "slcan: can't register line discipline\n");
+		kfree(slcan_devs);
+	}
+	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 == NULL)
+		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 */
+
+	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);
+}
+
+module_init(slcan_init);
+module_exit(slcan_exit);