os: log: consolidate log formatting functions

Simplify log formatting functions and remove redundancies, e.g.:

* common function for line termination
* copy prefix directly instead of *printf'ing it
* now just exactly one LogSWrite() call per message
  (good for other log targets like syslog)

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1691>

os/log.c

@@ -550,19 +550,6 @@ vpnprintf(char *string, int size_in, const char *f, va_list args)
     return s_idx;
 }
 
-static int
-pnprintf(char *string, int size, const char *f, ...)
-{
-    int rc;
-    va_list args;
-
-    va_start(args, f);
-    rc = vpnprintf(string, size, f, args);
-    va_end(args);
-
-    return rc;
-}
-
 /* This function does the actual log message writes. It must be signal safe.
  * When attempting to call non-signal-safe functions, guard them with a check
  * of the inSignalContext global variable. */
@@ -665,34 +652,50 @@ LogMessageTypeVerbString(MessageType type, int verb)
     }
 }
 
+#define LOG_MSG_BUF_SIZE 1024
+
+static ssize_t prepMsgHdr(MessageType type, int verb, char *buf)
+{
+    const char *type_str = LogMessageTypeVerbString(type, verb);
+    if (!type_str)
+        return -1;
+
+    size_t prefixLen = strlen_sigsafe(type_str);
+    if (prefixLen) {
+        memcpy(buf, type_str, prefixLen + 1); // rely on buffer being big enough
+        buf[prefixLen] = ' ';
+        prefixLen++;
+    }
+    buf[prefixLen] = 0;
+    return prefixLen;
+}
+
+static inline void writeLog(int verb, char *buf, int len)
+{
+    /* Force '\n' at end of truncated line */
+    if (LOG_MSG_BUF_SIZE  - len == 1)
+        buf[len - 1] = '\n';
+
+    LogSWrite(verb, buf, len, (buf[len - 1] == '\n'));
+}
+
 void
 LogVMessageVerb(MessageType type, int verb, const char *format, va_list args)
 {
-    const char *type_str;
+    char buf[LOG_MSG_BUF_SIZE];
-    char buf[1024];
-    size_t len = 0;
 
     if (inSignalContext) {
         LogVMessageVerbSigSafe(type, verb, format, args);
         return;
     }
 
-    type_str = LogMessageTypeVerbString(type, verb);
+    size_t len = prepMsgHdr(type, verb, buf);
-    if (!type_str)
+    if (len == -1)
         return;
 
-    /* if type_str is not "", prepend it and ' ', to message */
+    len += Xvscnprintf(&buf[len], sizeof(buf) - len, format, args);
-    if (type_str[0] != '\0')
-        len += Xscnprintf(&buf[len], sizeof(buf) - len, "%s ", type_str);
 
-    if (sizeof(buf) - len > 1)
+    writeLog(verb, buf, len);
-        len += Xvscnprintf(&buf[len], sizeof(buf) - len, format, args);
-
-    /* Force '\n' at end of truncated line */
-    if (sizeof(buf) - len == 1)
-        buf[len - 1] = '\n';
-
-    LogSWrite(verb, buf, len, (buf[len - 1] == '\n'));
 }
 
 /* Log message with verbosity level specified. */
@@ -730,68 +733,36 @@ LogMessageVerbSigSafe(MessageType type, int verb, const char *format, ...)
 void
 LogVMessageVerbSigSafe(MessageType type, int verb, const char *format, va_list args)
 {
-    const char *type_str;
+    char buf[LOG_MSG_BUF_SIZE];
-    char buf[1024];
-    int len;
 
-    type_str = LogMessageTypeVerbString(type, verb);
+    int len = prepMsgHdr(type, verb, buf);
-    if (!type_str)
+    if (len == -1)
         return;
 
-    /* if type_str is not "", prepend it and ' ', to message */
+    len += vpnprintf(&buf[len], sizeof(buf) - len, format, args);
-    if (type_str[0] != '\0') {
-        LogSWrite(verb, type_str, strlen_sigsafe(type_str), FALSE);
-        LogSWrite(verb, " ", 1, FALSE);
-    }
 
-    len = vpnprintf(buf, sizeof(buf), format, args);
+    writeLog(verb, buf, len);
-
-    /* Force '\n' at end of truncated line */
-    if (sizeof(buf) - len == 1)
-        buf[len - 1] = '\n';
-
-    LogSWrite(verb, buf, len, (len > 0 && buf[len - 1] == '\n'));
 }
 
 void
 LogVHdrMessageVerb(MessageType type, int verb, const char *msg_format,
                    va_list msg_args, const char *hdr_format, va_list hdr_args)
 {
-    const char *type_str;
+    char buf[LOG_MSG_BUF_SIZE];
-    char buf[1024];
-    size_t len = 0;
     int (*vprintf_func)(char *, int, const char* _X_RESTRICT_KYWD f, va_list args)
-            _X_ATTRIBUTE_PRINTF(3, 0);
+            _X_ATTRIBUTE_PRINTF(3, 0) = (inSignalContext ? vpnprintf : Xvscnprintf);
-    int (*printf_func)(char *, int, const char* _X_RESTRICT_KYWD f, ...)
-            _X_ATTRIBUTE_PRINTF(3, 4);
 
-    type_str = LogMessageTypeVerbString(type, verb);
+    size_t len = prepMsgHdr(type, verb, buf);
-    if (!type_str)
+    if (len == -1)
         return;
 
-    if (inSignalContext) {
-        vprintf_func = vpnprintf;
-        printf_func = pnprintf;
-    } else {
-        vprintf_func = Xvscnprintf;
-        printf_func = Xscnprintf;
-    }
-
-    /* if type_str is not "", prepend it and ' ', to message */
-    if (type_str[0] != '\0')
-        len += printf_func(&buf[len], sizeof(buf) - len, "%s ", type_str);
-
     if (hdr_format && sizeof(buf) - len > 1)
         len += vprintf_func(&buf[len], sizeof(buf) - len, hdr_format, hdr_args);
 
     if (msg_format && sizeof(buf) - len > 1)
         len += vprintf_func(&buf[len], sizeof(buf) - len, msg_format, msg_args);
 
-    /* Force '\n' at end of truncated line */
+    writeLog(verb, buf, len);
-    if (sizeof(buf) - len == 1)
-        buf[len - 1] = '\n';
-
-    LogSWrite(verb, buf, len, (buf[len - 1] == '\n'));
 }
 
 void