[t:2892] Improve comments.

git-svn-id: file:///svn/toku/tokudb@25736 c7de825b-a66e-492c-adef-691d508d4ae1

newbrt/log_upgrade.c

@@ -22,6 +22,7 @@ toku_log_upgrade_get_footprint(void) {
 #define FOOTPRINTCAPTURE footprint+=function_footprint;
 
 
+// return 0 if clean shutdown, TOKUDB_UPGRADE_FAILURE if not clean shutdown
 static int 
 verify_clean_shutdown_of_log_version_current(const char *log_dir, LSN * last_lsn) {
     int rval = TOKUDB_UPGRADE_FAILURE;
@@ -51,6 +52,7 @@ verify_clean_shutdown_of_log_version_current(const char *log_dir, LSN * last_lsn
 }
 
 
+// return 0 if clean shutdown, TOKUDB_UPGRADE_FAILURE if not clean shutdown
 static int 
 verify_clean_shutdown_of_log_version_old(const char *log_dir, LSN * last_lsn) {
     int rval = TOKUDB_UPGRADE_FAILURE;
@@ -67,7 +69,8 @@ verify_clean_shutdown_of_log_version_old(const char *log_dir, LSN * last_lsn) {
     char *basename;
     TOKULOGCURSOR cursor;
     struct log_entry *entry;
-    //Only look at newest log
+    // Only look at newest log
+    // basename points to first char after last / in file pathname
     basename = strrchr(logfiles[n_logfiles-1], '/') + 1;
     int version;
     long long index = -1;
@@ -103,7 +106,6 @@ verify_clean_shutdown_of_log_version_old(const char *log_dir, LSN * last_lsn) {
 static int
 verify_clean_shutdown_of_log_version(const char *log_dir, uint32_t version, LSN *last_lsn) {
     // return 0 if clean shutdown, TOKUDB_UPGRADE_FAILURE if not clean shutdown
-    // examine logfile at logfilenum and possibly logfilenum-1
     int r = 0;
     FOOTPRINTSETUP(1000);
 
@@ -121,6 +123,7 @@ verify_clean_shutdown_of_log_version(const char *log_dir, uint32_t version, LSN
 }
     
 
+// Actually create a log file of the current version, making the environment be of the current version.
 static int
 upgrade_log(const char *env_dir, const char *log_dir, LSN last_lsn) { // the real deal
     int r;
@@ -163,7 +166,8 @@ upgrade_log(const char *env_dir, const char *log_dir, LSN last_lsn) { // the rea
     return 0;
 }
 
-
+// If log on disk is old (environment is old) and clean shutdown, then create log of current version,
+// which will make the environment of the current version (and delete the old logs).
 int
 toku_maybe_upgrade_log(const char *env_dir, const char *log_dir, LSN * lsn_of_clean_shutdown, BOOL * upgrade_in_progress) {
     int r;