mux: fix ctrl-a b again

Commit fb5e19d originally fixed the
regression, but was inadvertently broken again in merge commit
2d6752d.

Fixes:
https://bugs.launchpad.net/qemu/+bug/1654137

Cc: qemu-stable@nongnu.org
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20180515152500.19460-3-f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

chardev/char-mux.c

@@ -304,6 +304,7 @@ void mux_set_focus(Chardev *chr, int focus)
     }
 
     d->focus = focus;
+    chr->be = d->backends[focus];
     mux_chr_send_event(d, d->focus, CHR_EVENT_MUX_IN);
 }
 

tests/test-char.c

@@ -214,6 +214,10 @@ static void char_mux_test(void)
     g_assert_cmpint(h2.last_event, ==, -1);
 
     /* switch focus */
+    qemu_chr_be_write(base, (void *)"\1b", 2);
+    g_assert_cmpint(h1.last_event, ==, 42);
+    g_assert_cmpint(h2.last_event, ==, CHR_EVENT_BREAK);
+
     qemu_chr_be_write(base, (void *)"\1c", 2);
     g_assert_cmpint(h1.last_event, ==, CHR_EVENT_MUX_IN);
     g_assert_cmpint(h2.last_event, ==, CHR_EVENT_MUX_OUT);
@@ -227,6 +231,10 @@ static void char_mux_test(void)
     g_assert_cmpstr(h1.read_buf, ==, "hello");
     h1.read_count = 0;
 
+    qemu_chr_be_write(base, (void *)"\1b", 2);
+    g_assert_cmpint(h1.last_event, ==, CHR_EVENT_BREAK);
+    g_assert_cmpint(h2.last_event, ==, CHR_EVENT_MUX_OUT);
+
     /* remove first handler */
     qemu_chr_fe_set_handlers(&chr_be1, NULL, NULL, NULL, NULL,
                              NULL, NULL, true);