-ERESTARTSYS and /dev/ttyS1

Riccardo Facchetti (fizban@mbox.vol.it)
Wed, 13 Nov 1996 22:46:56 +0100 (MET)

Hello Linuxers,

I have a problem that I can not explain myself (first time I see a
-ERESTARTSYS). I think it is related with libc libraries because this is
the first time I get this error, and the piece of code I will show you
worked fine until now, but I'm not sure when it have started this strange
I really need to know what's going on (this is the first _real problem_ I
have seen since running 2.0.24 kernel).

The system
i486/33 + 8MB RAM + 1 internal TRUST modem on ttyS1 + 1 sound card +
2 IDE interfaces ( 2 HD on the first + (1 HD + 1 CDROM) on the second)

Linux azuth 2.0.24 #1 Sat Nov 2 10:05:25 MET 1996 i486
gcc version
ld version 2.7 (with BFD

The problem
I have a modem on /dev/ttyS1 and I want to open the line and get a file
descriptor to talk with my modem.

The solution
static void alarm_jump(int sig) {
longjmp(not_opened, 1);
if (setjmp(not_opened) == 0) {
* build the modem device filename
sprintf(buffer, "/dev/%s", device->line);

* set up the alarm for jump if timeout
old_alarm_value = alarm(0);
old_alarm = signal(SIGALRM, alarm_jump);

fd = open(buffer, O_RDWR|O_NOCTTY);
* Restore the old alarm handler and scheduled timeout
signal(SIGALRM, old_alarm);
if (fd < 0)
return (mdmerrno = -EMDMOPEN);

The really strange behaviour
Follow the output of strace. Note the -ERESTARTSYS error. According with
/usr/include/linux/errno.h: /* Should never be seen by user programs */
open("/var/spool/uucp/LCK..ttyS1", O_RDONLY) = 3
read(3, " 2017\n", 128) = 11
close(3) = 0
kill(2017, SIGUSR1) = -1 ESRCH (No such process)
unlink("/var/spool/uucp/LCK..ttyS1") = 0
open("/var/spool/uucp/LCK..ttyS1", O_WRONLY|O_CREAT|O_EXCL, 03741) = 3
fchmod(3, 0644) = 0
getpid() = 2028
write(3, " 2028\n", 11) = 11
close(3) = 0
alarm(0) = 0
sigaction(SIGALRM, {0x8049230, [], SA_INTERRUPT|SA_NOMASK|SA_ONESHOT},
{SIG_DFL}) = 0
alarm(2) = 0
open("/dev/ttyS1", O_RDWR|O_NOCTTY) = -1 ERESTARTSYS (errno 512)
--- SIGALRM (Alarm clock) ---
alarm(0) = 0
sigaction(SIGALRM, {SIG_DFL}, {SIG_DFL}) = 0
alarm(0) = 0
write(2, "ldial failed: Can\'t open this l"..., 36ldial failed: Can't open
) = 36
_exit(-1) = ?

Some comments
While receiving that -ERESTARTSYS, I can hear my modem doing sounds like
as it is receiving an ATZ command.
Seems to me that my program lack some *black magic* initialization that
minicom have because I can * ??_reset_?? * (what reset, I just want to
open a device file !!!) the modem line (/dev/ttyS1) to its usual behaviour
just invoking minicom.
Of course I could go to minicom and see where is this *black magic*, and I
will do, but this post is mainly to report the -ERESTARTSYS error and of
course if someone have a better solution than go to minicom sources, will
be welcome :)

Ah of course there may be another reason this problem: I have
started to use dcon-0.96 to connect to my ISP. May be dcon do some strange
things with /dev/ttyS1, but the real problem is that strange -ERESTARTSYS.

Can a user program (dcon-0.96) set up the /dev/ttyS1 so that after close,
another program (my program) can not open() the same line, returning a
-ERESTARTSYS and a third program (minicom) can then *reset* it opening and
closing the device and giving the second program (my program) a clean
/dev/ttyS1 ?

The problem is 100% reproducible.