+ size_t len, cur = LOG_START_SZ;
+ va_list args;
+
+ do {
+ *buffer = calloc(1, cur);
+ if (!*buffer)
+ return 0;
+
+ va_copy(args, src_args);
+ len = vsnprintf(*buffer, cur, fmt, args);
+ va_end(args);
+
+ if (len < cur)
+ break;
+
+ cur = len + 1;
+ free(*buffer);
+ } while (1);
+
+ return len;
+}
+
+/* allocate buffer, fill with prefix string followed by vararg string */
+static size_t prevalist_to_buf(char **buffer, const char *pre, int prelen,
+ const char *fmt, va_list src_args)
+{
+ size_t len, cur = LOG_START_SZ;
+ va_list args;
+
+ do {
+ *buffer = calloc(1, cur);
+ if (!*buffer)
+ return 0;
+
+ va_copy(args, src_args);
+ memcpy(*buffer, pre, prelen);
+ len = prelen + vsnprintf(*buffer + prelen, cur - prelen, fmt, args);
+ va_end(args);
+
+ if (len < cur)
+ break;
+
+ cur = len + 1;
+ free(*buffer);
+ } while (1);
+
+ return len;
+}
+
+size_t log_valist(const char *fmt, va_list args)
+{
+ char *buffer;