[Qemu-devel] [PATCH 2/6] serial: reinstate watch after migration

[Paolo Bonzini <pbonzini@redhat.com>]

Otherwise, a serial port can get stuck if it is migrated while flow control
is in effect.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/char/serial.c         | 16 ++++++++++++++--
 include/hw/char/serial.h |  1 +
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/hw/char/serial.c b/hw/char/serial.c
index e65e9e0..6f0a49e 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -639,8 +639,20 @@ static int serial_post_load(void *opaque, int version_id)
     if (s->thr_ipending == -1) {
         s->thr_ipending = ((s->iir & UART_IIR_ID) == UART_IIR_THRI);
     }
-    if (s->tsr_retry > MAX_XMIT_RETRY) {
-        s->tsr_retry = MAX_XMIT_RETRY;
+
+    if (s->tsr_retry > 0) {
+        /* tsr_retry > 0 implies LSR.TEMT = 0 (transmitter not empty).  */
+        if (s->lsr & UART_LSR_TEMT) {
+            return -1;
+        }
+
+        assert(s->watch_tag == 0);
+        s->watch_tag = qemu_chr_fe_add_watch(s->chr, G_IO_OUT|G_IO_HUP, serial_xmit, s);
+    } else {
+        /* tsr_retry == 0 implies LSR.TEMT = 1 (transmitter empty).  */
+        if (!(s->lsr & UART_LSR_TEMT)) {
+            return -1;
+        }
     }
 
     s->last_break_enable = (s->lcr >> 6) & 1;
diff --git a/include/hw/char/serial.h b/include/hw/char/serial.h
index ef90615..2ab835c 100644
--- a/include/hw/char/serial.h
+++ b/include/hw/char/serial.h
@@ -56,6 +56,7 @@ struct SerialState {
     int it_shift;
     int baudbase;
     unsigned tsr_retry;
+    unsigned watch_tag;
     uint32_t wakeup;
 
     /* Time when the last byte was successfully sent out of the tsr */
-- 
2.5.5