char: forbid direct chardevice access for hotswap devices

qemu_chr_fe_get_driver() is unsafe, frontends with hotswap support
should not access CharDriver ptr directly as CharDriver might change.

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1499342940-56739-5-git-send-email-anton.nefedov@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/chardev/char-fe.c b/chardev/char-fe.c
index 7054863208..de5ba3c119 100644
--- a/chardev/char-fe.c
+++ b/chardev/char-fe.c
@@ -179,9 +179,16 @@ void qemu_chr_fe_printf(CharBackend *be, const char *fmt, ...)
 
 Chardev *qemu_chr_fe_get_driver(CharBackend *be)
 {
+    /* this is unsafe for the users that support chardev hotswap */
+    assert(be->chr_be_change == NULL);
     return be->chr;
 }
 
+bool qemu_chr_fe_backend_connected(CharBackend *be)
+{
+    return !!be->chr;
+}
+
 bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
 {
     int tag = 0;