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List:       busybox
Subject:    Re: serial console and log-in
From:       Denis Vlasenko <vda.linux () googlemail ! com>
Date:       2007-02-28 23:26:56
Message-ID: 200703010026.56844.vda.linux () googlemail ! com
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On Wednesday 28 February 2007 15:50, Natanael Copa wrote:
> > > I backported the svn init to 1.4.1 (i depend on releases).
> > > 
> > > My inittab line looks like this:
> > > 
> > > ::respawn:/sbin/getty - 9600 vt100
> > > 
> > > I got a login prompt but no controlling tty:
> > > 
> > > -ash: cant't access tty; job control turned off
> > > 
> > > ~$ echo TEST > /dev/tty
> > > -ash: cannot create /dev/tty: No such device or address
> > > 
> > > That was on a VGA console.
> > > 
> > > Then I tried to run it in qemu, with -nographic. It booted, it gave me a
> > > login, but same as VGA, no controlling tty.
> > 
> > I expected that. It stems from the fact that /dev/console
> > cannot be a ctty.
> > 
> > I'm not sure this can be classified as 'bug'.
> 
> Probably not. But then I need another feature :-/
> 
> Something like running a specified row only when controlling terminal is
> serial.
> 
> ttyS0:serial:respawn:/sbin/getty -L ttyS0 9600 vt100
> 
> Drawback is that it needs to use an unused field in inittab.

How about writing small hack which analyzes stdin (fd #0)
and closes fd #0,1,2 + reopens/dups /dev/ttyN or /dev/ttySn:


/* From <linux/vt.h> */
struct vt_stat {
        unsigned short v_active;        /* active vt */
        unsigned short v_signal;        /* signal to send */
        unsigned short v_state; /* vt bitmask */
};
enum { VT_GETSTATE = 0x5603 };  /* get global vt state info */

/* From <linux/serial.h> */
struct serial_struct {
        int     type;
        int     line;
        unsigned int    port;
        int     irq;
        int     flags;
        int     xmit_fifo_size;
        int     custom_divisor;
        int     baud_base;
        unsigned short  close_delay;
        char    io_type;
        char    reserved_char[1];
        int     hub6;
        unsigned short  closing_wait; /* time to wait before closing */
        unsigned short  closing_wait2; /* no longer used... */
        unsigned char   *iomem_base;
        unsigned short  iomem_reg_shift;
        unsigned int    port_high;
        unsigned long   iomap_base;     /* cookie passed into ioremap */
        int     reserved[1];
};

        int fd;
        struct vt_stat vt;
        struct serial_struct sr;
        char console[64];

        /* identify the real console backend and try to use it */
        if (ioctl(0, TIOCGSERIAL, &sr) == 0) {
                /* this is a serial console */
                snprintf(console, sizeof(console) - 1, "/dev/ttyS%d", sr.line);
        } else if (ioctl(0, VT_GETSTATE, &vt) == 0) {
                /* this is linux virtual tty */
                snprintf(console, sizeof(console) - 1, "/dev/tty%d", vt.v_active);
        } else {
               /* unable to figure it out */
               ...
        }

	fd = xopen(console, O_RDWR);
	dup2(fd, 0);
	dup2(fd, 1);
	dup2(fd, 2);
	while (fd > 2) close(fd--);

then exec it's argv?

Use it like this:

::respawn:/somewhere/cttyhack /sbin/getty - 9600 vt100

Care to try? ;)
--
vda
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