disallow -daemonize usage of stdio (curses display, -nographic, -serial stdio etc)

Curses display requires stdin/out to stay on the terminal,
so -daemonize makes no sense in this case.  Instead of
leaving display uninitialized like is done since 995ee2bf469de6bb,
explicitly detect this case earlier and error out.

-nographic can actually be used with -daemonize, by redirecting
everything to a null device, but the problem is that according
to documentation and historical behavour, -nographic redirects
guest ports to stdin/out, which, again, makes no sense in case
of -daemonize.  Since -nographic is a legacy option, don't bother
fixing this case (to allow -nographic and -daemonize by redirecting
guest ports to null instead of stdin/out in this case), but disallow
it completely instead, to stop garbling host terminal.

If no display display needed and user wants to use -nographic,
the right way to go is to use
  -serial null -parallel null -monitor none -display none -vga none
instead of -nographic.

Also prevent the same issue -- it was possible to get garbled
host tty after

  -nographic -daemonize

and it is still possible to have it by using

  -serial stdio -daemonize

Fix this by disallowing opening stdio chardev when -daemonize
is specified.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/qemu-char.c b/qemu-char.c
index c6382a9..331ad5c 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -772,6 +772,10 @@ static CharDriverState *qemu_chr_open_stdio(QemuOpts *opts)
     if (stdio_nb_clients >= STDIO_MAX_CLIENTS) {
         return NULL;
     }
+    if (is_daemonized()) {
+        error_report("cannot use stdio with -daemonize");
+        return NULL;
+    }
     if (stdio_nb_clients == 0) {
         old_fd0_flags = fcntl(0, F_GETFL);
         tcgetattr (0, &oldtty);