On 05/08/2013 01:12 PM, Wang YanQing wrote:
On Wed, May 08, 2013 at 11:18:07AM -0400, Peter Hurley wrote:
On 05/08/2013 09:16 AM, Wang YanQing wrote:
On Tue, May 07, 2013 at 07:02:00PM -0700, Greg KH wrote:
What about Peter's comments on this patch?
Peter's comments will import policy,
I means we should let userspace to decide whether
and when to restart tty with the mechanism of TCXONC
instead of restart tty accidental when make n_tty_set_termios
call.
There would be no accidental restart. Userspace is specifically
disabling user-controlled output flow control by clearing
IXON in termios. Userspace is _expecting_ a 'started' tty.
If you insist that this must be controllable from userspace,
then that is already possible:
tcflow(fd, TCOOFF);
tcflow(fd, TCOON);
Indeed you can't do what you said with TCOOFF and TCOON
if you read the codes, that's what this patch fix.
Perhaps you misunderstood. The snippet above does indeed restart
a tty which has been stopped via STOP_CHAR(tty) and the termios
IXON flag cleared.
Below is a testcase which demonstrates the problem and
the userspace workaround from above.
--- >% ---
/**
* tty_unstop.c
*
* Description: testcase for unsticking stopped tty from userspace
*
* To build testcase:
* gcc tty_unstop.c -o tty_unstop
*
* To build exemplar userspace workaround:
* gcc -D FIX_STOPPED_TTY tty_unstop.c -o tty_unstop
*/
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <stdarg.h>
static void error_exit(char *f, ...)
{
va_list va;
va_start(va, f);
vprintf(f, va);
printf(": %s\n", strerror(errno));
va_end(va);
exit(EXIT_FAILURE);
}
int main(int argc, char *argv[]) {
struct termios termios, save;
char buffer[MAX_CANON];
int err;
ssize_t n;
printf("Pause terminal now with Ctrl+S\n");
sleep(5);
err = tcgetattr(STDIN_FILENO, &termios);
if (err < 0)
error_exit("tcgetattr");
save = termios;
termios.c_iflag &= ~IXON;
err = tcsetattr(STDIN_FILENO, TCSANOW, &termios);
if (err < 0)
error_exit("tcsetattr");
#ifdef FIX_STOPPED_TTY
tcflow(STDIN_FILENO, TCOOFF);
tcflow(STDIN_FILENO, TCOON);
#endif
printf("Enter some text: ");
fflush(stdout);
n = read(STDIN_FILENO, buffer, sizeof(buffer));
if (n < 0)
error_exit("read");
printf("%.*s", (int)n, buffer);
err = tcsetattr(STDIN_FILENO, TCSAFLUSH, &save);
if (err < 0)
error_exit("tcsetattr");
return 0;
}
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