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can-utils/slcand.c
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Tomasz WasilczykandMarc Kleine-Budde 7a318636e7 slcand: Don't fail when it wasn't possible to fetch the interface name. 
On some systems SIOCGIFNAME may fail with ENOTTY, but the actual
slcanX interface gets properly configured. Instead of crashing hard on
such case, let's gracefuly degrade and just not display the interface
name.
2025-04-06 10:03:36 +02:00

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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* slcand.c - userspace daemon for serial line CAN interface driver SLCAN
*
* Copyright (c) 2009 Robert Haddon <robert.haddon@verari.com>
* Copyright (c) 2009 Verari Systems Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the version 2 of the GNU General Public License
* as published by the Free Software Foundation.
*
* 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, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* Send feedback to <linux-can@vger.kernel.org>
*
*/
#include <errno.h>
#include <fcntl.h>
#include <linux/serial.h>
#include <linux/sockios.h>
#include <linux/tty.h>
#include <net/if.h>
#include <pwd.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <syslog.h>
#include <termios.h>
#include <unistd.h>
/* Change this to whatever your daemon is called */
#define DAEMON_NAME "slcand"
/* Change this to the user under which to run */
#define RUN_AS_USER "root"
/* The length of ttypath buffer */
#define TTYPATH_LENGTH 256
/* UART flow control types */
#define FLOW_NONE 0
#define FLOW_HW 1
#define FLOW_SW 2
static void fake_syslog(int priority, const char *format, ...)
{
va_list ap;
printf("[%d] ", priority);
va_start(ap, format);
vprintf(format, ap);
va_end(ap);
printf("\n");
}
typedef void (*syslog_t)(int priority, const char *format, ...);
static syslog_t syslogger = syslog;
void print_usage(char *prg)
{
fprintf(stderr, "%s - userspace daemon for serial line CAN interface driver SLCAN.\n", prg);
fprintf(stderr, "\nUsage: %s [options] <tty> [canif-name]\n\n", prg);
fprintf(stderr, "Options:\n");
fprintf(stderr, " -o (send open command 'O\\r')\n");
fprintf(stderr, " -c (send close command 'C\\r')\n");
fprintf(stderr, " -f (read status flags with 'F\\r' to reset error states)\n");
fprintf(stderr, " -l (send listen only command 'L\\r', overrides -o)\n");
fprintf(stderr, " -s <speed> (set CAN speed 0..8)\n");
fprintf(stderr, " -S <speed> (set UART speed in baud)\n");
fprintf(stderr, " -t <type> (set UART flow control type 'hw' or 'sw')\n");
fprintf(stderr, " -b <btr> (set bit time register value)\n");
fprintf(stderr, " -F (stay in foreground; no daemonize)\n");
fprintf(stderr, " -h (show this help page)\n");
fprintf(stderr, "\nExamples:\n");
fprintf(stderr, "slcand -o -c -f -s6 ttyUSB0\n\n");
fprintf(stderr, "slcand -o -c -f -s6 ttyUSB0 can0\n\n");
fprintf(stderr, "slcand -o -c -f -s6 /dev/ttyUSB0\n\n");
exit(EXIT_FAILURE);
}
static int slcand_running;
static volatile sig_atomic_t exit_code;
static char ttypath[TTYPATH_LENGTH];
static void child_handler(int signum)
{
switch (signum) {
case SIGUSR1:
/* exit parent */
exit(EXIT_SUCCESS);
break;
case SIGINT:
case SIGTERM:
case SIGALRM:
case SIGCHLD:
syslogger(LOG_NOTICE, "received signal %i on %s", signum, ttypath);
exit_code = 128 + signum;
slcand_running = 0;
break;
}
}
static int look_up_uart_speed(long int s)
{
switch (s) {
case 9600:
return B9600;
case 19200:
return B19200;
case 38400:
return B38400;
case 57600:
return B57600;
case 115200:
return B115200;
case 230400:
return B230400;
case 460800:
return B460800;
case 500000:
return B500000;
case 576000:
return B576000;
case 921600:
return B921600;
case 1000000:
return B1000000;
case 1152000:
return B1152000;
case 1500000:
return B1500000;
case 2000000:
return B2000000;
#ifdef B2500000
case 2500000:
return B2500000;
#endif
#ifdef B3000000
case 3000000:
return B3000000;
#endif
#ifdef B3500000
case 3500000:
return B3500000;
#endif
#ifdef B3710000
case 3710000:
return B3710000;
#endif
#ifdef B4000000
case 4000000:
return B4000000;
#endif
default:
return -1;
}
}
int main(int argc, char *argv[])
{
char *tty = NULL;
char const *devprefix = "/dev/";
char *name = NULL;
char buf[20];
static struct ifreq ifr;
struct termios tios;
speed_t old_ispeed;
speed_t old_ospeed;
int opt;
int send_open = 0;
int send_close = 0;
int send_listen = 0;
int send_read_status_flags = 0;
char *speed = NULL;
char *uart_speed_str = NULL;
long int uart_speed = 0;
int flow_type = FLOW_NONE;
char *btr = NULL;
int run_as_daemon = 1;
char *pch;
int ldisc = N_SLCAN;
int fd;
ttypath[0] = '\0';
while ((opt = getopt(argc, argv, "ocfls:S:t:b:?hF")) != -1) {
switch (opt) {
case 'o':
send_open = 1;
break;
case 'c':
send_close = 1;
break;
case 'f':
send_read_status_flags = 1;
break;
case 'l':
send_listen = 1;
break;
case 's':
speed = optarg;
if (strlen(speed) > 1)
print_usage(argv[0]);
break;
case 'S':
uart_speed_str = optarg;
errno = 0;
uart_speed = strtol(uart_speed_str, NULL, 10);
if (errno)
print_usage(argv[0]);
if (look_up_uart_speed(uart_speed) == -1) {
fprintf(stderr, "Unsupported UART speed (%lu)\n", uart_speed);
exit(EXIT_FAILURE);
}
break;
case 't':
if (!strcmp(optarg, "hw")) {
flow_type = FLOW_HW;
} else if (!strcmp(optarg, "sw")) {
flow_type = FLOW_SW;
} else {
fprintf(stderr, "Unsupported flow type (%s)\n", optarg);
exit(EXIT_FAILURE);
}
break;
case 'b':
btr = optarg;
if (strlen(btr) > 8)
print_usage(argv[0]);
break;
case 'F':
run_as_daemon = 0;
break;
case 'h':
case '?':
default:
print_usage(argv[0]);
break;
}
}
if (!run_as_daemon)
syslogger = fake_syslog;
/* Initialize the logging interface */
openlog(DAEMON_NAME, LOG_PID, LOG_LOCAL5);
/* Parse serial device name and optional can interface name */
tty = argv[optind];
if (NULL == tty)
print_usage(argv[0]);
name = argv[optind + 1];
if (name && (strlen(name) > sizeof(ifr.ifr_newname) - 1))
print_usage(argv[0]);
/* Prepare the tty device name string */
pch = strstr(tty, devprefix);
if (pch != tty)
snprintf(ttypath, TTYPATH_LENGTH, "%s%s", devprefix, tty);
else
snprintf(ttypath, TTYPATH_LENGTH, "%s", tty);
syslogger(LOG_INFO, "starting on TTY device %s", ttypath);
fd = open(ttypath, O_RDWR | O_NONBLOCK | O_NOCTTY);
if (fd < 0) {
syslogger(LOG_NOTICE, "failed to open TTY device %s\n", ttypath);
perror(ttypath);
exit(EXIT_FAILURE);
}
/* Configure baud rate */
memset(&tios, 0, sizeof(tios));
if (tcgetattr(fd, &tios) < 0) {
syslogger(LOG_NOTICE, "failed to get attributes for TTY device %s: %s\n", ttypath, strerror(errno));
exit(EXIT_FAILURE);
}
// Because of a recent change in linux - https://patchwork.kernel.org/patch/9589541/
// we need to set low latency flag to get proper receive latency
struct serial_struct snew;
ioctl (fd, TIOCGSERIAL, &snew);
snew.flags |= ASYNC_LOW_LATENCY;
ioctl (fd, TIOCSSERIAL, &snew);
/* Get old values for later restore */
old_ispeed = cfgetispeed(&tios);
old_ospeed = cfgetospeed(&tios);
/* Reset UART settings */
cfmakeraw(&tios);
tios.c_iflag &= ~IXOFF;
tios.c_cflag &= ~CRTSCTS;
/* Baud Rate */
cfsetispeed(&tios, look_up_uart_speed(uart_speed));
cfsetospeed(&tios, look_up_uart_speed(uart_speed));
/* Flow control */
if (flow_type == FLOW_HW)
tios.c_cflag |= CRTSCTS;
else if (flow_type == FLOW_SW)
tios.c_iflag |= (IXON | IXOFF);
/* apply changes */
if (tcsetattr(fd, TCSADRAIN, &tios) < 0)
syslogger(LOG_NOTICE, "Cannot set attributes for device \"%s\": %s!\n", ttypath, strerror(errno));
if (speed) {
sprintf(buf, "C\rS%s\r", speed);
if (write(fd, buf, strlen(buf)) <= 0) {
perror("write");
exit(EXIT_FAILURE);
}
}
if (btr) {
sprintf(buf, "C\rs%s\r", btr);
if (write(fd, buf, strlen(buf)) <= 0) {
perror("write");
exit(EXIT_FAILURE);
}
}
if (send_read_status_flags) {
sprintf(buf, "F\r");
if (write(fd, buf, strlen(buf)) <= 0) {
perror("write");
exit(EXIT_FAILURE);
}
}
if (send_listen) {
sprintf(buf, "L\r");
if (write(fd, buf, strlen(buf)) <= 0) {
perror("write");
exit(EXIT_FAILURE);
}
} else if (send_open) {
sprintf(buf, "O\r");
if (write(fd, buf, strlen(buf)) <= 0) {
perror("write");
exit(EXIT_FAILURE);
}
}
/* set slcan like discipline on given tty */
if (ioctl(fd, TIOCSETD, &ldisc) < 0) {
perror("ioctl TIOCSETD");
exit(EXIT_FAILURE);
}
/* retrieve the name of the created CAN netdevice */
if (ioctl(fd, SIOCGIFNAME, ifr.ifr_name) < 0) {
if (name) {
perror("ioctl SIOCGIFNAME");
exit(EXIT_FAILURE);
} else {
/* Graceful degradation: we only needed the name for display. */
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "<unknown>");
}
}
syslogger(LOG_NOTICE, "attached TTY %s to netdevice %s\n", ttypath, ifr.ifr_name);
/* try to rename the created netdevice */
if (name) {
int s = socket(PF_INET, SOCK_DGRAM, 0);
if (s < 0)
perror("socket for interface rename");
else {
/* current slcan%d name is still in ifr.ifr_name */
memset (ifr.ifr_newname, 0, sizeof(ifr.ifr_newname));
strncpy (ifr.ifr_newname, name, sizeof(ifr.ifr_newname) - 1);
if (ioctl(s, SIOCSIFNAME, &ifr) < 0) {
syslogger(LOG_NOTICE, "netdevice %s rename to %s failed\n", buf, name);
perror("ioctl SIOCSIFNAME rename");
exit(EXIT_FAILURE);
} else
syslogger(LOG_NOTICE, "netdevice %s renamed to %s\n", buf, name);
close(s);
}
}
/* Daemonize */
if (run_as_daemon) {
if (daemon(0, 0)) {
syslogger(LOG_ERR, "failed to daemonize");
exit(EXIT_FAILURE);
}
}
else {
/* Trap signals that we expect to receive */
signal(SIGINT, child_handler);
signal(SIGTERM, child_handler);
}
slcand_running = 1;
/* The Big Loop */
while (slcand_running)
sleep(1); /* wait 1 second */
/* Reset line discipline */
syslogger(LOG_INFO, "stopping on TTY device %s", ttypath);
ldisc = N_TTY;
if (ioctl(fd, TIOCSETD, &ldisc) < 0) {
perror("ioctl TIOCSETD");
exit(EXIT_FAILURE);
}
if (send_close) {
sprintf(buf, "C\r");
if (write(fd, buf, strlen(buf)) <= 0) {
perror("write");
exit(EXIT_FAILURE);
}
}
/* Reset old rates */
cfsetispeed(&tios, old_ispeed);
cfsetospeed(&tios, old_ospeed);
/* apply changes */
if (tcsetattr(fd, TCSADRAIN, &tios) < 0)
syslogger(LOG_NOTICE, "Cannot set attributes for device \"%s\": %s!\n", ttypath, strerror(errno));
/* Finish up */
syslogger(LOG_NOTICE, "terminated on %s", ttypath);
closelog();
return exit_code;
}
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