Fix emacsclient terminal corruption when in background.

* emacsclient.c (handle_sigcont): Check for tcgetpgrp failure.
Cancel the continue only if tty.  Send SIGTTIN to the process
group, not SIGSTOP to self, as this is what the glibc manual
recommends.
(main): If tty, and if started in the background, send SIGTTIN
to the process group.

Fixes: debbugs:16892

2 files changed, 23 insertions, 3 deletions

diff --git a/lib-src/ChangeLog b/lib-src/ChangeLog
index 8cf73cea5d6..0c3d7d723c5 100644
--- a/lib-src/ChangeLog
+++ b/lib-src/ChangeLog
@@ -1,3 +1,13 @@
+2014-03-09  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Fix emacsclient terminal corruption when in background (Bug#16892).
+        * emacsclient.c (handle_sigcont): Check for tcgetpgrp failure.
+        Cancel the continue only if tty.  Send SIGTTIN to the process
+        group, not SIGSTOP to self, as this is what the glibc manual
+        recommends.
+        (main): If tty, and if started in the background, send SIGTTIN
+        to the process group.
+
 2014-02-25  Andreas Amann  <a.amann@ucc.ie>  (tiny change)
 
         Fix emacsclient's handling of SIGCONT (Bug#16883).
diff --git a/lib-src/emacsclient.c b/lib-src/emacsclient.c
index 148182a6ccf..cf16874589d 100644
--- a/lib-src/emacsclient.c
+++ b/lib-src/emacsclient.c
@@ -1105,16 +1105,18 @@ static void
 handle_sigcont (int signalnum)
 {
   int old_errno = errno;
+  pid_t pgrp = getpgrp ();
+  pid_t tcpgrp = tcgetpgrp (1);
 
-  if (tcgetpgrp (1) == getpgrp ())
+  if (tcpgrp == pgrp)
     {
       /* We are in the foreground.  */
       send_to_emacs (emacs_socket, "-resume \n");
     }
-  else if (tty)
+  else if (0 <= tcpgrp && tty)
     {
       /* We are in the background; cancel the continue.  */
-      raise (SIGSTOP);
+      kill (-pgrp, SIGTTIN);
     }
 
   signal (signalnum, handle_sigcont);
@@ -1554,6 +1556,14 @@ main (int argc, char **argv)
       exit (EXIT_FAILURE);
     }
 
+  if (tty)
+    {
+      pid_t pgrp = getpgrp ();
+      pid_t tcpgrp = tcgetpgrp (1);
+      if (0 <= tcpgrp && tcpgrp != pgrp)
+        kill (-pgrp, SIGTTIN);
+    }
+
   /* If alternate_editor is the empty string, start the emacs daemon
      in case of failure to connect.  */
   start_daemon_if_needed = (alternate_editor