fixed serial console for syslinux

usr/share/rear/conf/default.conf

@@ -2904,8 +2904,15 @@ SIMPLIFY_TEAMING=no
 # are set when booting the rescue/recovery system (see KERNEL_CMDLINE above).
 # IA64 platforms do require it, and sometimes people still use serial console
 # e.g. when no VGA console is available (say y, n or leave empty to autodetect):
+# This config value may change in the near future and may merge with SERIAL_CONSOLE_DEVICE_SYSLINUX.
 USE_SERIAL_CONSOLE=
 
+# Since syslinux does not work with more then one serial device at once it must be explicitly named.
+# Here you can configute the serial console device to use e.g. 'SERIAL_CONSOLE_DEVICE_SYSLINUX=/dev/ttyS0' when USE_SERIAL_CONSOLE is turned on.
+# By default (when unset) all found serial devices are used.
+# This config value may change in the near future and may get merged with USE_SERIAL_CONSOLE.
+SERIAL_CONSOLE_DEVICE_SYSLINUX=
+
 # Say "y", "Yes", etc, to enable or "n", "No" etc. to disable the DHCP client protocol or leave empty to autodetect.
 # When enabled, lets the rescue/recovery system run dhclient to get an IP address
 # instead of using the same IP address as the original system:

usr/share/rear/lib/bootloader-functions.sh

@@ -199,12 +199,17 @@ function make_syslinux_config {
         SYSLINUX_DIR="$syslinux_modules_dir"
     fi
 
-    # Enable serial console, unless explicitly disabled (only last entry is used :-/)
+    # Enable serial console, unless explicitly disabled (only last entry is used on some systems thats where SERIAL_CONSOLE_DEVICE_SYSLINUX comes in :-/)
     if [[ "$USE_SERIAL_CONSOLE" =~ ^[yY1] ]]; then
         for devnode in $(ls /dev/ttyS[0-9]* | sort); do
-            speed=$(stty -F $devnode 2>/dev/null | awk '/^speed / { print $2 }')
-            if [ "$speed" ]; then
-                echo "serial ${devnode##/dev/ttyS} $speed"
+            # Not sure if using all serial devices do screw up syslinux in general
+            # for me listing more then one serial line in the config screwed it
+            # see https://github.com/rear/rear/pull/2650
+            if [ -z $SERIAL_CONSOLE_DEVICE_SYSLINUX ] || [[ $SERIAL_CONSOLE_DEVICE_SYSLINUX == $devnode ]]; then
+                speed=$(stty -F $devnode 2>/dev/null | awk '/^speed / { print $2 }')
+                if [ "$speed" ]; then
+                    echo "serial ${devnode##/dev/ttyS} $speed"
+                fi
             fi
         done
     fi

usr/share/rear/output/USB/Linux-i386/300_create_extlinux.sh

@@ -264,9 +264,14 @@ Log "Creating $SYSLINUX_PREFIX/extlinux.conf"
     # Enable serial console, unless explicitly disabled
     if [[ "$USE_SERIAL_CONSOLE" =~ ^[yY1] ]]; then
         for devnode in $(ls /dev/ttyS[0-9]* | sort); do
-            speed=$(stty -F $devnode 2>/dev/null | awk '/^speed / { print $2 }')
-            if [ "$speed" ]; then
-                syslinux_write "serial ${devnode##/dev/ttyS} $speed"
+            # Not sure if using all serial devices do screw up syslinux in general
+            # for me listing more then one serial line in the config screwed it
+            # see https://github.com/rear/rear/pull/2650
+            if [ -z $SERIAL_CONSOLE_DEVICE_SYSLINUX ] || [[ $SERIAL_CONSOLE_DEVICE_SYSLINUX == $devnode ]]; then
+                speed=$(stty -F $devnode 2>/dev/null | awk '/^speed / { print $2 }')
+                if [ "$speed" ]; then
+                    syslinux_write "serial ${devnode##/dev/ttyS} $speed"
+                fi
             fi
         done
     fi