[PATCH v4 17/23] util: fix interleaving of error prefixes

["Daniel P. Berrangé" <berrange@redhat.com>]

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.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 util/error-report.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/util/error-report.c b/util/error-report.c
index 222c40d0d1..b6aa20dbae 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 {
+        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) {
+        funlockfile(stderr);
+    }
 }
 
 /*
-- 
2.50.1