If xenconsole (the client program) fails, it calls err.  This would
previously neglect to reset the user's terminal to sanity.  Use atexit
to do so.

This routinely happens in Xen 4.4 RC5 with pygrub because something
writes the value "" to the tty xenstore key when using xenconsole.
The cause of this is not yet known, but after this patch it just
results in a harmless error message.

Reported-by: M A Young <m.a.young@xxxxxxxxxxxx>
Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CC: M A Young <m.a.young@xxxxxxxxxxxx>
CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 tools/console/client/main.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/console/client/main.c b/tools/console/client/main.c
index eb6a1a9..62159f6 100644
--- a/tools/console/client/main.c
+++ b/tools/console/client/main.c
@@ -257,6 +257,13 @@ typedef enum {
        CONSOLE_SERIAL,
 } console_type;
 
+static struct termios stdin_old_attr;
+
+static void restore_term_stdin(void)
+{
+       restore_term(STDIN_FILENO, &stdin_old_attr);
+}
+
 int main(int argc, char **argv)
 {
 	struct termios attr;
@@ -383,9 +390,9 @@ int main(int argc, char **argv)
 	}
 
 	init_term(spty, &attr);
-	init_term(STDIN_FILENO, &attr);
+	init_term(STDIN_FILENO, &stdin_old_attr);
+	 atexit(restore_term_stdin); /* if this fails, oh dear */
 	console_loop(spty, xs, path);
-	restore_term(STDIN_FILENO, &attr);
 
 	free(path);
 	free(dom_path);
-- 
1.7.10.4
Since 28d386fc4341 (XSA-57), libxl writes an empty value for the
console tty node, with read-only permission for the guest, when
setting up pv console "frontends".  (The actual tty value is later set
by xenconsoled.)   Writing an empty node is not strictly necessary to
stop the frontend from writing dangerous values here, but it is a good
belt-and-braces approach.

Unfortunately this confuses xenconsole.  It reads the empty value, and
tries to open it as the tty.  xenconsole then exits.

Fix this by having xenconsole treat an empty value the same way as no
value at all.

Also, make the error opening the tty be nonfatal: we just print a
warning, but do not exit.  I think this is helpful in theoretical
situations where xenconsole is racing with libxl and/or xenconsoled.

Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 tools/console/client/main.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/console/client/main.c b/tools/console/client/main.c
index 62159f6..b882345 100644
--- a/tools/console/client/main.c
+++ b/tools/console/client/main.c
@@ -115,9 +115,11 @@ static int get_pty_fd(struct xs_handle *xs, char *path, int seconds)
 			 * disambiguate: just read the pty path */
 			pty_path = xs_read(xs, XBT_NULL, path, &len);
 			if (pty_path != NULL) {
-				pty_fd = open(pty_path, O_RDWR | O_NOCTTY);
-				if (pty_fd == -1)
-					err(errno, "Could not open tty `%s'", pty_path);
+				if (pty_path[0] != '\0') {
+					pty_fd = open(pty_path, O_RDWR | O_NOCTTY);
+					if (pty_fd == -1)
+						warn("Could not open tty `%s'", pty_path);
+				}
 				free(pty_path);
 			}
 		}
-- 
1.7.10.4