tty: n_gsm: add ioctl to map serial device to mux'ed tty

Guessing the first tty for a gsm0710 multiplexed serial device is not
currently possible, which makes it racy to use with multiple modems.

Add a way to map the physical serial tty to its related mux devices
using an ioctl.

Signed-off-by: Martin Hundebøll <martin@geanix.com>
Link: https://lore.kernel.org/r/20190812211243.98686-1-martin@geanix.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/driver-api/serial/n_gsm.rst b/Documentation/driver-api/serial/n_gsm.rst
index 0ba731a..286e7ff 100644 (file)
--- a/Documentation/driver-api/serial/n_gsm.rst
+++ b/Documentation/driver-api/serial/n_gsm.rst
@@ -18,10 +18,13 @@ How to use it
 2. switch the serial line to using the n_gsm line discipline by using
    TIOCSETD ioctl,
 3. configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl,
+4. obtain base gsmtty number for the used serial port,
 
 Major parts of the initialization program :
 (a good starting point is util-linux-ng/sys-utils/ldattach.c)::
 
+  #include <stdio.h>
+  #include <stdint.h>
   #include <linux/gsmmux.h>
   #include <linux/tty.h>
   #define DEFAULT_SPEED        B115200
@@ -30,6 +33,7 @@ Major parts of the initialization program :
        int ldisc = N_GSM0710;
        struct gsm_config c;
        struct termios configuration;
+       uint32_t first;
 
        /* open the serial port connected to the modem */
        fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
@@ -58,19 +62,22 @@ Major parts of the initialization program :
        c.mtu = 127;
        /* set the new configuration */
        ioctl(fd, GSMIOC_SETCONF, &c);
+       /* get first gsmtty device node */
+       ioctl(fd, GSMIOC_GETFIRST, &first);
+       printf("first muxed line: /dev/gsmtty%i\n", first);
 
        /* and wait for ever to keep the line discipline enabled */
        daemon(0,0);
        pause();
 
-4. use these devices as plain serial ports.
+5. use these devices as plain serial ports.
 
    for example, it's possible:
 
    - and to use gnokii to send / receive SMS on ttygsm1
    - to use ppp to establish a datalink on ttygsm2
 
-5. first close all virtual ports before closing the physical port.
+6. first close all virtual ports before closing the physical port.
 
    Note that after closing the physical port the modem is still in multiplexing
    mode. This may prevent a successful re-opening of the port later. To avoid

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index a60be59..d305259 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2613,6 +2613,7 @@ static int gsmld_ioctl(struct tty_struct *tty, struct file *file,
 {
        struct gsm_config c;
        struct gsm_mux *gsm = tty->disc_data;
+       unsigned int base;
 
        switch (cmd) {
        case GSMIOC_GETCONF:
@@ -2624,6 +2625,9 @@ static int gsmld_ioctl(struct tty_struct *tty, struct file *file,
                if (copy_from_user(&c, (void *)arg, sizeof(c)))
                        return -EFAULT;
                return gsm_config(gsm, &c);
+       case GSMIOC_GETFIRST:
+               base = mux_num_to_base(gsm);
+               return put_user(base + 1, (__u32 __user *)arg);
        default:
                return n_tty_ioctl_helper(tty, file, cmd, arg);
        }

diff --git a/include/uapi/linux/gsmmux.h b/include/uapi/linux/gsmmux.h
index 101d3c4..cb8693b 100644 (file)
--- a/include/uapi/linux/gsmmux.h
+++ b/include/uapi/linux/gsmmux.h
@@ -37,5 +37,7 @@ struct gsm_netconfig {
 #define GSMIOC_ENABLE_NET      _IOW('G', 2, struct gsm_netconfig)
 #define GSMIOC_DISABLE_NET     _IO('G', 3)
 
+/* get the base tty number for a configured gsmmux tty */
+#define GSMIOC_GETFIRST                _IOR('G', 4, __u32)
 
 #endif