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Hello, Kernel Hackers!
I am using kernel version 2.1.76. Today, I tried a program called
9term (it's a terminal emulator for X) and wondered why did it exit
right after pressing a key. To my amusement, the program died because
of an oops (attached, but looks weird). The kernel stumbled in
tty_ioctl().
The following patch cures the problem, but probably not the cause:
[cut here]
--- /usr/src/linux/drivers/char/tty_io.c- Sat Dec 27 19:29:29 1997
+++ /usr/src/linux/drivers/char/tty_io.c Sat Dec 27 19:52:54 1997
@@ -1548,13 +1548,17 @@
switch(cmd) {
case TIOCSBRK:
case TIOCCBRK:
- return tty->driver.ioctl(tty, file, cmd, arg);
+ if (tty->driver.ioctl)
+ return tty->driver.ioctl(tty, file, cmd, arg);
+ return -ENOIOCTLCMD;
/* These two ioctl's always return success; even if */
/* the driver doesn't support them. */
case TCSBRK:
- case TCSBRKP:
- retval = tty->driver.ioctl(tty, file, cmd, arg);
+ case TCSBRKP:
+ retval = 0;
+ if (tty->driver.ioctl)
+ retval = tty->driver.ioctl(tty, file, cmd, arg);
if (retval == -ENOIOCTLCMD)
retval = 0;
return retval;
[cut here]
The oops was triggered because tty->driver.ioctl was a NULL pointer
(the ptys don't have driver.ioctl?). This makes me wonder what would
be the right fix? Should ptys have ioctl()? A simple one would do
pretty well:
pty_driver_ioctl(...)
{
return -ENOIOCTLCMD;
}
Or some such... But clearly the current behavior is broken, since an
usermode program reproducibly triggers an oops...
(BTW, what use is 9term? Couldn't think of any...)
Taneli <vahakang@cs.helsinki.fi>
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