[PATCH v4 08/23] log: avoid repeated prefix on incremental qemu_log calls

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

Some code makes multiple qemu_log calls to incrementally emit
a single message. Currently timestamps get prepended to all
qemu_log calls, even those continuing a previous incomplete
message.

This changes the qemu_log so it skips adding a new line prefix,
if the previous qemu_log call did NOT end with a newline.

Fixes: 012842c07552 (log: make '-msg timestamp=on' apply to all qemu_log usage)
Reported-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Dr. David Alan Gilbert <dave@treblig.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 util/log.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/util/log.c b/util/log.c
index abdcb6b311..2642a55c59 100644
--- a/util/log.c
+++ b/util/log.c
@@ -143,6 +143,12 @@ void qemu_log_unlock(FILE *logfile)
     }
 }
 
+/*
+ * 'true' if the previous log message lacked a trailing '\n',
+ * and thus the subsequent call must skip any prefix
+ */
+static __thread bool incomplete;
+
 void qemu_log(const char *fmt, ...)
 {
     FILE *f;
@@ -154,7 +160,7 @@ void qemu_log(const char *fmt, ...)
      * was emitted if we are delayed acquiring the
      * mutex
      */
-    if (message_with_timestamp) {
+    if (message_with_timestamp && !incomplete) {
         g_autoptr(GDateTime) dt = g_date_time_new_now_utc();
         timestr = g_date_time_format_iso8601(dt);
     }
@@ -170,6 +176,7 @@ void qemu_log(const char *fmt, ...)
         va_start(ap, fmt);
         vfprintf(f, fmt, ap);
         va_end(ap);
+        incomplete = fmt[strlen(fmt) - 1] != '\n';
         qemu_log_unlock(f);
     }
 }
-- 
2.50.1