chardev: Use timer instead of bottom-half to postpone open event

As the block layer may decide to flush bottom-halfs while the machine is
still initializing (e.g. to read geometry data from the disk), our
postponed open event may be processed before the last frontend
registered with a muxed chardev.

Until the semantics of BHs have been clarified, use an expired timer to
achieve the same effect (suggested by Paolo Bonzini). This requires to
perform the alarm timer initialization earlier as otherwise timer
subsystem can be used before being ready.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

3 files changed, 13 insertions, 12 deletions

diff --git a/qemu-char.c b/qemu-char.c
index afe2bfb4dd..88f40254b7 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -123,19 +123,20 @@ void qemu_chr_be_event(CharDriverState *s, int event)
     s->chr_event(s->handler_opaque, event);
 }
 
-static void qemu_chr_generic_open_bh(void *opaque)
+static void qemu_chr_fire_open_event(void *opaque)
 {
     CharDriverState *s = opaque;
     qemu_chr_be_event(s, CHR_EVENT_OPENED);
-    qemu_bh_delete(s->bh);
-    s->bh = NULL;
+    qemu_free_timer(s->open_timer);
+    s->open_timer = NULL;
 }
 
 void qemu_chr_generic_open(CharDriverState *s)
 {
-    if (s->bh == NULL) {
-	s->bh = qemu_bh_new(qemu_chr_generic_open_bh, s);
-	qemu_bh_schedule(s->bh);
+    if (s->open_timer == NULL) {
+        s->open_timer = qemu_new_timer_ms(vm_clock,
+                                          qemu_chr_fire_open_event, s);
+        qemu_mod_timer(s->open_timer, qemu_get_clock_ms(vm_clock) - 1);
     }
 }
 
diff --git a/qemu-char.h b/qemu-char.h
index 486644b3bd..297dd98342 100644
--- a/qemu-char.h
+++ b/qemu-char.h
@@ -69,7 +69,7 @@ struct CharDriverState {
     void (*chr_guest_open)(struct CharDriverState *chr);
     void (*chr_guest_close)(struct CharDriverState *chr);
     void *opaque;
-    QEMUBH *bh;
+    QEMUTimer *open_timer;
     char *label;
     char *filename;
     int opened;
diff --git a/vl.c b/vl.c
index 5a3d316980..5513d1518e 100644
--- a/vl.c
+++ b/vl.c
@@ -3551,6 +3551,11 @@ int main(int argc, char **argv, char **envp)
             add_device_config(DEV_VIRTCON, "vc:80Cx24C");
     }
 
+    if (init_timer_alarm() < 0) {
+        fprintf(stderr, "could not initialize alarm timer\n");
+        exit(1);
+    }
+
     socket_init();
 
     if (qemu_opts_foreach(qemu_find_opts("chardev"), chardev_init_func, NULL, 1) != 0)
@@ -3618,11 +3623,6 @@ int main(int argc, char **argv, char **envp)
 
     os_set_line_buffering();
 
-    if (init_timer_alarm() < 0) {
-        fprintf(stderr, "could not initialize alarm timer\n");
-        exit(1);
-    }
-
 #ifdef CONFIG_SPICE
     /* spice needs the timers to be initialized by this point */
     qemu_spice_init();