[Qemu-devel] [PATCH v2] chardev: Use timer instead of bottom-half to postpone open event

[Jan Kiszka]

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.kis...@siemens.com>
---

Changes in v2:
 - Move init_alarm_timer call to fix e.g. -monitor stdio

 qemu-char.c |   13 +++++++------
 qemu-char.h |    2 +-
 vl.c        |   10 +++++-----
 3 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/qemu-char.c b/qemu-char.c
index b082bae..d8eed21 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 486644b..297dd98 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 5b357a3..586773c 100644
--- a/vl.c
+++ b/vl.c
@@ -3439,6 +3439,11 @@ 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)
@@ -3506,11 +3511,6 @@ 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();
-- 
1.7.3.4