armbian-next: logging: squash nasty leaking file descriptor bug due to "tee"

- check and make sure the fd is closed before processing and/or deleting logs.
- change from fd 3 to 13, for extra "this is evil". is it? is 13 an evil number? you decide.

lib/functions/logging/logging.sh

@@ -100,7 +100,26 @@ function print_current_asset_log_base_file() {
 	echo -n "${ASSET_LOGFILE_BASE}"
 }
 
+function check_and_close_fd_13() {
+	if [[ -e /proc/self/fd/13 ]]; then
+		display_alert "Closing fd 13" "log still open" "cleanup"
+		exec 13>&- || true # close the file descriptor, lest sed keeps running forever.
+		display_alert "Waiting for tee to finish" "if it's still running" "cleanup"
+		wait || true # wait for the tee process to finish
+		display_alert "Done waiting for tee/fd13" "it's gone" "cleanup"
+	else
+		display_alert "fd 13 is not open" "nothing to do" "cleanup"
+	fi
+}
+
 function discard_logs_tmp_dir() {
+	# if we're in a logging section and logging to file when an error happened, and we're now cleaning up,
+	# the "tee" process created for fd 13 in do_with_logging() is still running, and holding a reference to the log file,
+	# which resides precisely in LOGDIR. So we need to kill it.
+
+	# Check if fd 13 is still open; close it and wait for tee to die.
+	check_and_close_fd_13
+	
 	# Do not delete the dir itself, since it might be a tmpfs mount.
 	if [[ "$(uname)" == "Linux" ]]; then
 		rm -rf --one-file-system "${LOGDIR:?}"/* # Note this is protected by :?

lib/functions/logging/section-logging.sh

@@ -49,15 +49,16 @@ function do_with_logging() {
 		prefix_sed_contents="$(logging_echo_prefix_for_pv "tool")   $(echo -n -e "${tool_color}")" # spaces are significant
 		local prefix_sed_cmd="s/^/${prefix_sed_contents}/;"
 
-		# This is sick. Create a 3rd file descriptor sending it to sed. https://unix.stackexchange.com/questions/174849/redirecting-stdout-to-terminal-and-file-without-using-a-pipe
+		# Create a 13rd file descriptor sending it to sed. https://unix.stackexchange.com/questions/174849/redirecting-stdout-to-terminal-and-file-without-using-a-pipe
 		# Also terrible: don't hold a reference to cwd by changing to SRC always
-		exec 3> >(
+		# There's handling of this fd 13 in check_and_close_fd_13()
+		exec 13> >(
 			cd "${SRC}" || exit 2
 			# First, log to file, then add prefix via sed for what goes to screen.
 			tee -a "${CURRENT_LOGFILE}" | sed -u -e "${prefix_sed_cmd}"
 		)
-		"$@" >&3
-		exec 3>&- # close the file descriptor, lest sed keeps running forever.
+		"$@" >&13
+		exec 13>&- # close the file descriptor, lest sed keeps running forever.
 	else
 		# If not showing the log, just send stdout to logfile. stderr will flow to screen.
 		"$@" >> "${CURRENT_LOGFILE}"

lib/functions/logging/trap-logging.sh

@@ -19,6 +19,9 @@ function trap_handler_cleanup_logging() {
 	local target_path="${DEST}/logs"
 	mkdir_recursive_and_set_uid_owner "${target_path}" # @TODO: this might be full of logs and is slow
 
+	# Check if fd 13 is still open; close it and wait for tee to die. This is done again in discard_logs_tmp_dir()
+	check_and_close_fd_13
+
 	# Before writing new logfile, compress and move existing ones to archive folder.
 	# - Unless running under CI.
 	# - Also not if signalled via SKIP_LOG_ARCHIVE=yes
@@ -29,10 +32,10 @@ function trap_handler_cleanup_logging() {
 		for one_old_logfile in "${existing_log_files_array[@]}"; do
 			old_logfile_fn="$(basename "${one_old_logfile}")"
 			if [[ "${old_logfile_fn}" == *${ARMBIAN_BUILD_UUID}* ]]; then
-				display_alert "Skipping archiving of current logfile" "${old_logfile_fn}" "warn"
+				display_alert "Skipping archiving of current logfile" "${old_logfile_fn}" "cleanup"
 				continue
 			fi
-			display_alert "Archiving old logfile" "${old_logfile_fn}" "warn"
+			display_alert "Archiving old logfile" "${old_logfile_fn}" "cleanup"
 			mkdir_recursive_and_set_uid_owner "${target_archive_path}" # @TODO: slow
 
 			# Check if we have `zstdmt` at this stage; if not, use standard gzip