vl: Print error when using incorrect backend for debugcon

When using an incorrect backend for the debugcon, QEMU exits silently
without any error indication, which is confusing.
Add a message that the character backend is invalid.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20181011171254.32428-1-philmd@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/vl.c b/vl.c
index 4e25c78bff..61305b5891 100644
--- a/vl.c
+++ b/vl.c
@@ -2466,6 +2466,7 @@ static int debugcon_parse(const char *devname)
     QemuOpts *opts;
 
     if (!qemu_chr_new_mux_mon("debugcon", devname)) {
+        error_report("invalid character backend '%s'", devname);
         exit(1);
     }
     opts = qemu_opts_create(qemu_find_opts("device"), "debugcon", 1, NULL);