File 0102-hw-char-serial-Only-retry-if-qemu_c.patch of Package qemu-testsuite.19805

From: Sergio Lopez <slp@redhat.com>
Date: Tue, 5 Jun 2018 03:54:55 -0400
Subject: hw/char/serial: Only retry if qemu_chr_fe_write returns 0

Only retry on serial_xmit if qemu_chr_fe_write returns 0, as this is the
only recoverable error.

Retrying with any other scenario, in addition to being a waste of CPU
cycles, can compromise the Guest stability if by the vCPU issuing the
write and the main loop thread are, by chance or explicit pinning,
running on the same pCPU.

Previous discussion:

https://lists.nongnu.org/archive/html/qemu-devel/2018-05/msg06998.html

Signed-off-by: Sergio Lopez <slp@redhat.com>
Message-Id: <1528185295-14199-1-git-send-email-slp@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 019288bf137183bf3407c9824655b753bfafc99f)
[LY: BSC#1108474]
Signed-off-by: Liang Yan <lyan@suse.com>
---
 hw/char/serial.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/char/serial.c b/hw/char/serial.c
index eb72191ee7665469386d82deffc3..9936fa20d348fe739f573a084bbf 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -261,7 +261,7 @@ static void serial_xmit(SerialState *s)
         if (s->mcr & UART_MCR_LOOP) {
             /* in loopback mode, say that we just received a char */
             serial_receive1(s, &s->tsr, 1);
-        } else if (qemu_chr_fe_write(&s->chr, &s->tsr, 1) != 1 &&
+        } else if (qemu_chr_fe_write(&s->chr, &s->tsr, 1) == 0 &&
                    s->tsr_retry < MAX_XMIT_RETRY) {
             assert(s->watch_tag == 0);
             s->watch_tag =