[Qemu-devel] PATCH: Put Psuedo-TTY in rawmode for char devices

[Daniel P. Berrange]

If running a QEMU instance with a serial/parallel device connected to a
Psuedo-TTY, eg  '-serial pty',  every \r\n sequence output by the guest
is getting translated into a \n\n sequence by the TTY layer. So clients
interacting with the serial port via a TTY done get the correct \r\n
sequence and text marches to the right and wraps. This is because the 
TTY is not put into rawmode when QEMU sets it up. 

The following patch is a re-diff of a patch applied to Xen's QEMU code.
It uses cfmakeraw() to ensure the TTY is put into rawmode, thus avoiding
the incorrect \r\n translations. It also switches to tcsetattr() on the
slave_fd instead of master_fd - although this is effectively the same on
Linux, only slave_fd works on Solaris. Finally it stops using the 'name'
arg to openpty() which is a security risk because its buffer size is
undefined. Instead it makes use of the ptsname() function.

Regards,
Daniel.

Index: vl.c
===================================================================
--- vl.c        (revision 4229)
+++ vl.c        (working copy)
@@ -2275,24 +2275,20 @@
 static CharDriverState *qemu_chr_open_pty(void)
 {
     struct termios tty;
-    char slave_name[1024];
     int master_fd, slave_fd;
 
 #if defined(__linux__)
     /* Not satisfying */
-    if (openpty(&master_fd, &slave_fd, slave_name, NULL, NULL) < 0) {
+    if (openpty(&master_fd, &slave_fd, NULL, NULL, NULL) < 0) {
         return NULL;
     }
 #endif
 
-    /* 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);
+    /* Set raw attributes on the pty. */
+    cfmakeraw(&tty);
+    tcsetattr(slave_fd, TCSAFLUSH, &tty);
 
-    fprintf(stderr, "char device redirected to %s\n", slave_name);
+    fprintf(stderr, "char device redirected to %s\n", ptsname(master_fd));
     return qemu_chr_open_fd(master_fd, master_fd);
 }
 


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