From ba96da130a625a71b574c1bb9f6027e3b8d655ab Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Fri, 9 Jun 2017 11:43:59 +0200
Subject: [PATCH 4/6] serial: reinstate watch after migration

RH-Author: Paolo Bonzini <pbonzini@redhat.com>
Message-id: <20170609114359.13036-4-pbonzini@redhat.com>
Patchwork-id: 75566
O-Subject: [RHEL7.4 qemu-kvm PATCH v2 3/3] serial: reinstate watch after migration
Bugzilla: 1452067
RH-Acked-by: David Hildenbrand <david@redhat.com>
RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>

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

Tested-by: Bret Ketchum <bcketchum@gmail.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 9f34a35e0020b0b2b2e21c086a486d7dfd18df4f)
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/char/serial.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/hw/char/serial.c b/hw/char/serial.c
index 0518a6f..820960b 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -637,13 +637,34 @@ static int serial_post_load(void *opaque, int version_id)
     if (version_id < 3) {
         s->fcr_vmstate = 0;
     }
-    if (s->tsr_retry > MAX_XMIT_RETRY) {
-        s->tsr_retry = MAX_XMIT_RETRY;
-    }
-
     if (s->thr_ipending == -1) {
         s->thr_ipending = ((s->iir & UART_IIR_ID) == UART_IIR_THRI);
     }
+
+    if (s->tsr_retry > 0) {
+        /* tsr_retry > 0 implies LSR.TEMT = 0 (transmitter not empty).  */
+        if (s->lsr & UART_LSR_TEMT) {
+            error_report("inconsistent state in serial device "
+                         "(tsr empty, tsr_retry=%d", s->tsr_retry);
+            return -1;
+        }
+
+        if (s->tsr_retry > MAX_XMIT_RETRY) {
+            s->tsr_retry = MAX_XMIT_RETRY;
+        }
+
+        assert(s->watch_tag == 0);
+        s->watch_tag = qemu_chr_fe_add_watch(s->chr, G_IO_OUT|G_IO_HUP,
+                                             serial_watch_cb, s);
+    } else {
+        /* tsr_retry == 0 implies LSR.TEMT = 1 (transmitter empty).  */
+        if (!(s->lsr & UART_LSR_TEMT)) {
+            error_report("inconsistent state in serial device "
+                         "(tsr not empty, tsr_retry=0");
+            return -1;
+        }
+    }
+
     s->last_break_enable = (s->lcr >> 6) & 1;
     /* Initialize fcr via setter to perform essential side-effects */
     serial_write_fcr(s, s->fcr_vmstate);
-- 
1.8.3.1