Adding removable-usb keyword to further restrict live media selection.

manpages/live-initramfs.en.7.txt

@@ -116,7 +116,8 @@ for block devices is performed.
 
 Instead of specifing an actual device name, the keyword 'removable' can be used
 to limit the search of acceptable live media to removable type only. Note that
-cdrom devices are not removable, but e.g. usb mass storage is.
+if you want to further restrict the media to usb mass storage only, you can use
+the 'removable-usb' keyword.
 
   {live-media-encryption|encryption}=**TYPE**::
 

scripts/live

@@ -1418,6 +1418,22 @@ find_livefs ()
 			done
 			;;
 
+		removable-usb)
+			for sysblock in $(echo /sys/block/* | tr ' ' '\n' | grep -vE "/(loop|ram|dm-|fd)")
+			do
+				if [ "$(cat ${sysblock}/removable)" = "1" ] && readlink ${sysblock}/device | grep -q usb
+				then
+					for dev in $(subdevices "${sysblock}")
+					do
+						if check_dev "${dev}"
+						then
+							return 0
+						fi
+					done
+				fi
+			done
+			;;
+
 		*)
 			if [ ! -z "${LIVE_MEDIA}" ]
 			then