Re: [PATCH] n_tty_read: check for hanging tty while waiting for input

From: Aristeu Rozanski
Date: Wed Feb 18 2015 - 09:58:21 EST

Hi Peter,
On Tue, Feb 17, 2015 at 05:35:10PM -0500, Peter Hurley wrote:
> I realize that. But hanging up the tty that is /dev/console only affects
> open descriptors that are not /dev/console.
> So readers using the /dev/ttyS0 file descriptor will see a hungup fops,
> but readers using /dev/console will not, and /dev/ttyS0 will _not_
> be closed or released because of the still-open descriptor on /dev/console.

I see.

> Ok, so the process sleeping on /dev/console read() should have received
> SIGHUP, which would wake the process and cause it to exit the
> n_tty_read() loop, thus dropping the ldisc reference it holds.
> Did it ignore the signal or perhaps the signal is masked?

Not masked on the test case (attached). Sent sighup manually and it did
receive it.


#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <termios.h>
#include <errno.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <sys/ioctl.h>

static char *default_console = "/dev/console";
static char *default_tty = "/dev/ttyS0";
struct data {
char *console;
char *tty;

static void *reader(void *d)
struct data *data = (struct data *)d;
struct termios old_termio;
char buff[512];
int fd = -1, rc;

while (1) {
if (fd == -1) {
fd = open(data->console, O_RDWR);
if (fd < 0)
if (tcgetattr(fd, &old_termio) == -1)
old_termio.c_lflag = ICANON;
if (tcsetattr(fd, 0, &old_termio) == -1)
rc = read(fd, buff, sizeof(buff));
if (rc < 0 && errno == EAGAIN)
fd = -1;

void launch(void *(*fn)(void *), struct data *data)
if (fork() == 0)

int main(int argc, char *argv[])
struct data data;
int fd;

fd = open("/dev/ttyS0", O_RDWR);
ioctl(fd, TIOCSCTTY, 1);

data.console = default_console;
data.tty = default_tty;

launch(reader, &data);

waitpid(-1, NULL, 0);

return 0;

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