Subject: tools/console: xenconsole tolerate tty errors
From: Ian Jackson ian.jackson@eu.citrix.com Thu Feb 27 17:46:49 2014 +0000
Date: Wed Mar 19 13:37:19 2014 +0000:
Git: 39ba2989b10b6a1852e253b204eb010f8e7026f1

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@eu.citrix.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>
CC: George Dunlap <george.dunlap@eu.citrix.com>

---
v2: Combine two conditions and move the free

Index: xen-4.4.0-testing/tools/console/client/main.c
===================================================================
--- xen-4.4.0-testing.orig/tools/console/client/main.c
+++ xen-4.4.0-testing/tools/console/client/main.c
@@ -115,12 +115,12 @@ static int get_pty_fd(struct xs_handle *
 			/* We only watch for one thing, so no need to 
 			 * disambiguate: just read the pty path */
 			pty_path = xs_read(xs, XBT_NULL, path, &len);
-			if (pty_path != NULL) {
+			if (pty_path != NULL && pty_path[0] != '\0') {
 				pty_fd = open(pty_path, O_RDWR | O_NOCTTY);
 				if (pty_fd == -1)
-					err(errno, "Could not open tty `%s'", pty_path);
-				free(pty_path);
+					warn("Could not open tty `%s'", pty_path);
 			}
+			free(pty_path);
 		}
 	} while (pty_fd == -1 && (now = time(NULL)) < start + seconds);