sys/log: Address review comments

- Fix syscfg description
- Remove log_trailer_data_len API and underlying callback as it doesn't
get used anywhere
- Revert API protoype style change in log.h

Author: vrahane

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

@@ -135,16 +135,6 @@ typedef int log_process_trailer_func_t(struct log *log, void *arg, const void *d
  */
 typedef uint16_t log_trailer_len_func_t(struct log *log, const struct log_entry_hdr *hdr);
 
-/** @typedef log_trailer_data_len_func_t
- * @brief Callback used to read length of trailer data in a log entry
- *
- * @param log                   The log the trailer is to be read from
- * @param hdr                   Log entry header of the log entry the log is
- *                              read from
- * @return                      Length of the appended trailer data
- */
-typedef uint16_t log_trailer_data_len_func_t(struct log *log, const struct log_entry_hdr *hdr);
-
 /** @typedef log_trailer_reset_data_func_t
  * @brief Callback used to reset trailer data per log
  *
@@ -311,11 +301,23 @@ STATS_SECT_END
 
 /* Trailer support callbacks */
 struct log_trailer_handler {
+    /* Trailer length callback used to get the length of the trailer from provided
+     * log entry
+     */
     log_trailer_len_func_t *log_trailer_len;
-    log_trailer_data_len_func_t *log_trailer_data_len;
+    /* Trailer append callback used to append trailer to the log entry */
     log_trailer_append_func_t *log_trailer_append;
+    /* Trailer process callback used to process trailer from the log entry
+     * which gets called at various places where the log entry gets read
+     */
     log_process_trailer_func_t *log_process_trailer;
+    /* Trailer mbuf append callback used to append trailer to the log entry
+     * using the mbufs
+     */
     log_trailer_mbuf_append_func_t *log_trailer_mbuf_append;
+    /* Trailer reset data callback used to reset the trailer data
+     * per log which is defined by the application registering these callbacks
+     */
     log_trailer_reset_data_func_t *log_trailer_reset_data;
 };
 
@@ -663,7 +665,8 @@ int log_read_hdr(struct log *log, const void *dptr, struct log_entry_hdr *hdr);
  *
  * @return Length of the header
  */
-uint16_t log_hdr_len(const struct log_entry_hdr *hdr);
+uint16_t
+log_hdr_len(const struct log_entry_hdr *hdr);
 
 /**
  * @brief Reads data from the body of a log entry into a flat buffer.
@@ -881,15 +884,6 @@ int log_len_in_medium(struct log *log, uint16_t len);
  */
 uint16_t log_trailer_len(struct log *log, const struct log_entry_hdr *hdr);
 
-/**
- * @brief Reads the trailer data length
- *
- * @param hdr    Ptr to the header
- *
- * @return Length of the trailer data
- */
-uint16_t log_trailer_data_len(struct log *log, const struct log_entry_hdr *hdr);
-
 /**
  * @brief Append trailer to the log entry
  *

sys/log/full/src/log.c

@@ -524,19 +524,6 @@ log_trailer_len(struct log *log, const struct log_entry_hdr *hdr)
     return 0;
 }
 
-uint16_t
-log_trailer_data_len(struct log *log, const struct log_entry_hdr *hdr)
-{
-    if (log->l_th) {
-        if (log->l_th->log_trailer_data_len) {
-            return log->l_th->log_trailer_data_len(log, hdr);
-        } else {
-            return 0;
-        }
-    }
-    return 0;
-}
-
 int
 log_trailer_append(struct log *log, uint8_t *buf, uint16_t *buflen,
                    void *loc, uint16_t *f_offset)
@@ -692,7 +679,9 @@ log_append_prepare(struct log *log, uint8_t module, uint8_t level,
 #endif
 
 #if MYNEWT_VAL(LOG_FLAGS_TRAILER_SUPPORT)
-    ue->ue_flags |= LOG_FLAGS_TRAILER_SUPPORT;
+    if (log->l_th) {
+        ue->ue_flags |= LOG_FLAGS_TRAILER_SUPPORT;
+    }
 #endif
 
 err:

sys/log/full/syscfg.yml

@@ -65,7 +65,7 @@ syscfg.defs:
 
     LOG_FLAGS_TRAILER_SUPPORT:
         description: >
-            Enable logging TLV with custom data types in every log entry
+            Enable logging trailer with custom data types in every log entry
             0 - disable; 1 - enable.
         value: 0