sys/log: Fix trailer length offset in log_fcb

- Trailer buffer pointer, data and callbacks should not be zeroed out
  on registeration. This is because log_registeration does not just
  initialize the fields, it also reads the most recent log entry to
  update the index and also call a custom init callback which can be
  reading the trailer.
- The trailer_alignment of 0 was making the offset for the
  trailer_len to be wrong. Now, we do not try to copy padding
  for the trailer_alignment if it is 0. This change along with the
  removal of zeroing out the trailer info in the log structure
  was causing the tests to fail since the offset was wrong. Correcting
  the trailer_len offset fixes everything.
- Make log_trailer_cbs_register experimental
- This is to allow log registeration for trailers
  in a combined fashion

Author: vrahane

sys/log/full/include/log/log.h

@@ -667,7 +667,10 @@ log_trailer_reset_data(struct log *log, void *arg)
 }
 
 /**
- * @brief Register trailer callbacks
+ * @brief Register trailer callbacks, this is an experimental API
+ *        and may be changed/deprecated later. This needs to be
+ *        called before log_register() if the trailer data needs
+ *        to be initialized when the log gets registered.
  *
  * @param log            The log to read from.
  * @param lth            The trailer handler to register.

sys/log/full/src/log.c

@@ -437,6 +437,9 @@ log_read_last_hdr(struct log *log, struct log_entry_hdr *out_hdr)
 
 /*
  * Associate an instantiation of a log with the logging infrastructure
+ * If trailer data needs to be read, the trailer callbacks should be
+ * registered before calling this function. They are set using
+ * log_trailer_cbs_register().
  */
 int
 log_register(const char *name, struct log *log, const struct log_handler *lh,
@@ -462,12 +465,6 @@ log_register(const char *name, struct log *log, const struct log_handler *lh,
     log->l_idx = 0;
 #endif
 
-#if MYNEWT_VAL(LOG_FLAGS_TRAILER)
-    log->l_tr_om = NULL;
-    log->l_tr_arg = NULL;
-    log->l_th = NULL;
-#endif
-
     if (!log_registered(log)) {
 #if MYNEWT_VAL(LOG_STATS)
         stats_init(STATS_HDR(log->l_stats),

sys/log/full/src/log_fcb.c

@@ -542,6 +542,7 @@ log_fcb_append_mbuf_body(struct log *log, const struct log_entry_hdr *hdr,
     struct fcb_log *fcb_log;
     int len;
     int rc;
+    uint16_t buflen = 0;
 #if MYNEWT_VAL(LOG_FLAGS_TRAILER)
     int trailer_alignment = 0;
     uint8_t pad[LOG_FCB_MAX_ALIGN] = {0};
@@ -558,7 +559,8 @@ log_fcb_append_mbuf_body(struct log *log, const struct log_entry_hdr *hdr,
         return SYS_ENOTSUP;
     }
 
-    len = log_hdr_len(hdr) + os_mbuf_len(om);
+    buflen = os_mbuf_len(om);
+    len = log_hdr_len(hdr) + buflen;
 
 #if MYNEWT_VAL(LOG_FLAGS_TRAILER)
     if (hdr->ue_flags & LOG_FLAGS_TRAILER) {
@@ -616,10 +618,12 @@ log_fcb_append_mbuf_body(struct log *log, const struct log_entry_hdr *hdr,
          */
 
         if (log->l_tr_om) {
-            /* Copy mbuf chain len */
-            rc = os_mbuf_copyinto(om, trailer_len, pad, trailer_alignment);
-            if (rc) {
-                return rc;
+            if (trailer_alignment) {
+                /* Copy padding for trailer alignment */
+                rc = os_mbuf_copyinto(om, buflen, pad, trailer_alignment);
+                if (rc) {
+                    return rc;
+                }
             }
 
             /* Append from the trailer */
@@ -630,8 +634,8 @@ log_fcb_append_mbuf_body(struct log *log, const struct log_entry_hdr *hdr,
 
             om = os_mbuf_pullup(om, LOG_TRAILER_LEN_SIZE);
             /* Copy the trailer length */
-            rc = os_mbuf_copyinto(om, trailer_len, &trailer_len,
-                                  LOG_TRAILER_LEN_SIZE);
+            rc = os_mbuf_copyinto(om, buflen + trailer_alignment + trailer_len,
+                                  &trailer_len, LOG_TRAILER_LEN_SIZE);
             if (rc) {
                 return rc;
             }