serial-log: Do not fail when tty is unavailable

I don't like the fact, that on most systems `systemctl status` shows
the state as degraded and that we have irrelevant entries in the journal,
just because we don't have a functioning ttyS1 available.

Regard serial.log\@ as a "best effort" service, which continuously tries
to work with the device and just waits a bit on failure.

Use an external command for the loop instead of abusing the service
restart feature of systemd for that.

install.sh

@@ -134,4 +134,5 @@ install_exec hostconfig/hostconfig                       "$DESTDIR$usr_sbindir/h
 install_exec fon/fon.sh                                  "$DESTDIR$usr_bindir/fon"
 install_exec nfsdtop/nfsdtop                             "$DESTDIR$usr_sbindir/nfsdtop"
 install_data serial-log/serial-log\@.service             "$DESTDIR$systemdunitdir/serial-log@.service"
+install_exec serial-log/serial-log                       "$DESTDIR$usr_exec_prefix/libexec/serial-log"
 exit

serial-log/serial-log

@@ -0,0 +1,14 @@
+#! /bin/bash
+
+(($#==1)) || { echo "usage: $0 device-name" >&2; exit 1; }
+
+devnam="$1"
+
+while true; do
+	until /usr/bin/stty -F "/dev/$devnam" 115200 -echo 2>/dev/null; do
+		sleep 60
+	done
+	until cat "/dev/$devnam" >> /var/log/$devnam.log 2>&1;do
+		sleep 1
+	done
+done

serial-log/serial-log@.service

@@ -2,11 +2,8 @@
 Description=TTY logger
 
 [Service]
-ExecStartPre=/usr/bin/stty -F /dev/%I 115200 -echo
-ExecStart=-/usr/bin/sh -c "/usr/bin/cat /dev/%I >> /var/log/%I.log 2>&1"
-Type=idle
-Restart=always
-RestartSec=0
+ExecStart=/usr/libexec/serial-log %I
+Type=simple
 UtmpIdentifier=%I
 
 [Install]