logging: Explain ERR_LOG_FILE && stdout redirection

Signed-off-by: Michał Iwanicki <[email protected]>

scripts/dts-boot

@@ -19,6 +19,8 @@ export DTS_VERBOSE_LOG_FILE
 export ERR_LOG_FILE
 export SHELLOPTS
 
+# $ERR_LOG_FILE is fd that can only be written to: '>()'. To copy logs
+# we need underlying file that can be copied
 ERR_LOG_FILE_REALPATH="/var/local/dts-err_$(basename "$(tty)").log"
 DTS_LOG_FILE="/tmp/dts_$(basename "$(tty)").log"
 DTS_VERBOSE_LOG_FILE="/tmp/dts-verbose_$(basename "$(tty)").log"
@@ -28,6 +30,8 @@ source "$BASH_ENV"
 start_trace_logging
 start_logging
 if [ -z "$ERR_LOG_FILE" ]; then
+    # pass everything written to $ERR_LOG_FILE to logger function and save it's
+    # output to $ERR_LOG_FILE_REALPATH file
     exec {ERR_LOG_FILE}> >(logger >> "$ERR_LOG_FILE_REALPATH")
     ERR_LOG_FILE="/proc/$$/fd/$ERR_LOG_FILE"
 fi

scripts/logging

@@ -10,8 +10,10 @@ logger() {
 start_logging() {
     local file="$DTS_LOG_FILE"
     if [ -z "$LOGGING" ]; then
-        LOGGING="Y"
+        LOGGING="true"
         if [ -z "$DESC" ]; then
+            # Create file descriptor that echoes back anything written to it
+            # and also logs that line to file with added timestamp prefix
             exec {DESC}> >(tee >(stdbuf -i0 -oL -eL ts "[%T]: " >> "$file"))
         fi
         exec 1>&$DESC