chardev: fix backend events regression with mux chardev

Kirill noticied that on recent versions on QEMU he was not able to
trigger SysRq to invoke debug capabilites of Linux Kernel.  He tracked
it down to qemu_chr_be_event() ignoring CHR_EVENT_BREAK due s->be
being NULL. The bug was introduced in 2.8, commit a4afa548fc6d ("char:
move front end handlers in CharBackend"). Since the commit, the
qemu_chr_be_event() failed to deliver CHR_EVENT_BREAK due to
qemu_chr_fe_init() does not set s->be in case of mux.

Let's fix this by teaching mux to send an event to the frontend with
the focus.

Reported-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Fixes: a4afa548fc6d ("char: move front end handlers in CharBackend")
Message-Id: <20171103152824.21948-2-marcandre.lureau@redhat.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/chardev/char.c b/chardev/char.c
index 2ae4f465ec..8c3765ee99 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -43,10 +43,19 @@ static Object *get_chardevs_root(void)
     return container_get(object_get_root(), "/chardevs");
 }
 
-void qemu_chr_be_event(Chardev *s, int event)
+static void chr_be_event(Chardev *s, int event)
 {
     CharBackend *be = s->be;
 
+    if (!be || !be->chr_event) {
+        return;
+    }
+
+    be->chr_event(be->opaque, event);
+}
+
+void qemu_chr_be_event(Chardev *s, int event)
+{
     /* Keep track if the char device is open */
     switch (event) {
         case CHR_EVENT_OPENED:
@@ -57,11 +66,7 @@ void qemu_chr_be_event(Chardev *s, int event)
             break;
     }
 
-    if (!be || !be->chr_event) {
-        return;
-    }
-
-    be->chr_event(be->opaque, event);
+    CHARDEV_GET_CLASS(s)->chr_be_event(s, event);
 }
 
 /* Not reporting errors from writing to logfile, as logs are
@@ -244,6 +249,7 @@ static void char_class_init(ObjectClass *oc, void *data)
     ChardevClass *cc = CHARDEV_CLASS(oc);
 
     cc->chr_write = null_chr_write;
+    cc->chr_be_event = chr_be_event;
 }
 
 static void char_finalize(Object *obj)