[RFC]: add a logging handler callback

Just some code to guide a discussion on how to add a logging callback
routine to make applications and bindings uses the various apis easier
to integrate into different logging mechanisms. This would be nice for
the Python bindings.

TODO:
1. Add ESAPI support
2. Add FAPI support
3. Test
4. Fiddle with names, style and locations in the code base

Signed-off-by: William Roberts <william.c.roberts@intel.com>

include/tss2/tss2_common.h

@@ -39,6 +39,10 @@ struct TSS2_ABI_VERSION {
 
 #define TSS2_ABI_VERSION_CURRENT {1, 2, 1, 108}
 
+/* TODO: Maybe this is better in tss2_log.h? */
+#include <stddef.h>
+typedef void (*TSS2_LOG_HANDLER)(const char *msg, size_t size);
+
 /*
  * Return Codes
  */

src/util/log.c

@@ -2,6 +2,7 @@
 #include <config.h>
 #endif
 
+#include <assert.h>
 #include <string.h>
 #include <stdio.h>
 #include <stdarg.h>
@@ -182,32 +183,55 @@ doLogBlob(log_level loglevel, const char *module, log_level logdefault,
     }
 }
 
+static void do_default_log(const char *msg, size_t size)
+{
+    FILE *logfile = getLogFile();
+    fwrite(msg, size, 1, logfile);
+    fflush(logfile);
+}
+
+static TSS2_LOG_HANDLER log_cb = do_default_log;
+
+TSS2_LOG_HANDLER set_log_handler(TSS2_LOG_HANDLER new_handler)
+{
+    TSS2_LOG_HANDLER old = log_cb;
+    log_cb = new_handler;
+    return old;
+}
+
 void
 doLog(log_level loglevel, const char *module, log_level logdefault,
            log_level *status,
            const char *file, const char *func, int line,
            const char *msg, ...)
 {
-    FILE *logfile;
-    if (unlikely(*status == LOGLEVEL_UNDEFINED))
-        *status = getLogLevel(module, logdefault);
-
-    if (loglevel > *status)
+    /* No logger set, skip */
+    if (!log_cb) {
         return;
+    /* Logger is default, so check the level */
+    } else if (log_cb == do_default_log) {
+
+        if (unlikely(*status == LOGLEVEL_UNDEFINED))
+            *status = getLogLevel(module, logdefault);
+
+        if (loglevel > *status)
+            return;
+    }
+
+    /* Any set logger gets called */
+    char fmt[1024];
+    char buf[4096];
 
-    int size = snprintf(NULL, 0, "%s:%s:%s:%d:%s() %s \n",
-                log_strings[loglevel], module, file, line, func, msg);
-    char fmt[size+1];
     snprintf(fmt, sizeof(fmt), "%s:%s:%s:%d:%s() %s \n",
                 log_strings[loglevel], module, file, line, func, msg);
 
     va_list vaargs;
     va_start(vaargs, msg);
-    logfile = getLogFile();
-    vfprintf (logfile, fmt,
+    int rc = vsnprintf (buf, sizeof(buf), fmt,
         /* log_strings[loglevel], module, file, func, line, */
         vaargs);
-    fflush(logfile);
+    assert(rc > 0);
+    log_cb(buf, (size_t)rc);
     va_end(vaargs);
 }
 

src/util/log.h

@@ -146,6 +146,8 @@ static log_level LOGMODULE_status COMPILER_ATTR(unused) = LOGLEVEL_UNDEFINED;
 #define LOGBLOB_TRACE(FORMAT, ...) {}
 #endif
 
+TSS2_LOG_HANDLER set_log_handler(TSS2_LOG_HANDLER new_handler);
+
 void
 doLog(log_level loglevel, const char *module, log_level logdefault,
        log_level *status,