By default, with qemu version < 0.8.0 and with the command line
qemu -monitor pty or -serial pty, local echo is
enabled for the qemu side of the pty. This can result in infinite
write/read loops and/or slowness of the simulation. Attached is a very
small patch (against today's cvs) solving the problem. The 3 lines
adjusting the tty fields could be replaced by "cfmakeraw(&tty)" if
available on the host platform.

  -- David Decotigny (Dec 9 2005)


Index: vl.c
===================================================================
RCS file: /cvsroot/qemu/qemu/vl.c,v
retrieving revision 1.152
diff -u -r1.152 vl.c
--- vl.c	5 Dec 2005 20:31:52 -0000	1.152
+++ vl.c	9 Dec 2005 15:07:46 -0000
@@ -1396,6 +1396,7 @@
 #if defined(__linux__)
 CharDriverState *qemu_chr_open_pty(void)
 {
+    struct termios tty;
     char slave_name[1024];
     int master_fd, slave_fd;
     
@@ -1403,6 +1404,14 @@
     if (openpty(&master_fd, &slave_fd, slave_name, NULL, NULL) < 0) {
         return NULL;
     }
+    
+    /* Disabling local echo and line-buffered output */
+    tcgetattr (master_fd, &tty);
+    tty.c_lflag &= ~(ECHO|ICANON|ISIG);
+    tty.c_cc[VMIN] = 1;
+    tty.c_cc[VTIME] = 0;
+    tcsetattr (master_fd, TCSAFLUSH, &tty);
+
     fprintf(stderr, "char device redirected to %s\n", slave_name);
     return qemu_chr_open_fd(master_fd, master_fd);
 }