[PATCH v5 18/24] util: fix interleaving of error prefixes

The vreport() function will optionally emit an prefix for error
messages which is output to stderr incrementally. In the event
that two vreport() calls execute concurrently, there is a risk
that the prefix output will interleave. To address this it is
required to take a lock on 'stderr' when outputting errors.

Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Daniel P. Berrangé <[email protected]>
---
 util/error-report.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/util/error-report.c b/util/error-report.c
index 14b170ca4c..46ea9ededa 100644
--- a/util/error-report.c
+++ b/util/error-report.c
@@ -226,6 +226,8 @@ static void vreport(report_type type, const char *fmt, va_list ap)
 
     if (monitor_cur_is_hmp()) {
         cur = monitor_cur();
+    } else {
+        qemu_flockfile(stderr);
     }
 
     if (message_with_timestamp && !cur) {
@@ -254,6 +256,10 @@ static void vreport(report_type type, const char *fmt, va_list ap)
 
     error_vprintf_mon(cur, fmt, ap);
     error_printf_mon(cur, "\n");
+
+    if (!cur) {
+        qemu_funlockfile(stderr);
+    }
 }
 
 /*
-- 
2.52.0