Under the conditions that UML uses it, tcgetattr is guaranteed to
return -EINTR when the console is attached to /dev/ptmx, making
generic_console_write hang because it loops, calling tcgetattr until
it succeeds. This is a host bug - see
http://marc.info/?l=linux-kernel&m=119618990807182&w=2 for the
details.
This patch works around it by blocking SIGIO while the terminal
attributes are being fiddled.
Signed-off-by: Jeff Dike <[email protected]>
---
arch/um/drivers/chan_user.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
Index: linux-2.6.22/arch/um/drivers/chan_user.c
===================================================================
--- linux-2.6.22.orig/arch/um/drivers/chan_user.c 2007-11-21 11:43:50.000000000 -0500
+++ linux-2.6.22/arch/um/drivers/chan_user.c 2007-11-27 14:03:10.000000000 -0500
@@ -74,10 +74,16 @@ void generic_free(void *data)
int generic_console_write(int fd, const char *buf, int n)
{
+ sigset_t old, no_sigio;
struct termios save, new;
int err;
if (isatty(fd)) {
+ sigemptyset(&no_sigio);
+ sigaddset(&no_sigio, SIGIO);
+ if (sigprocmask(SIG_BLOCK, &no_sigio, &old))
+ goto error;
+
CATCH_EINTR(err = tcgetattr(fd, &save));
if (err)
goto error;
@@ -97,8 +103,11 @@ int generic_console_write(int fd, const
* Restore raw mode, in any case; we *must* ignore any error apart
* EINTR, except for debug.
*/
- if (isatty(fd))
+ if (isatty(fd)) {
CATCH_EINTR(tcsetattr(fd, TCSAFLUSH, &save));
+ sigprocmask(SIG_SETMASK, &old, NULL);
+ }
+
return err;
error:
return -errno;