common: new function to get real device path name and basename

If TEST_DEV or SCRATCH_DEV is symlink(mostly a lvm lv), a simple
basename is not enough, symlink should be followed.

This task is common enough, so introduce new helper functions and
replace all readlink calls in

ext4/305
generic/009
generic/019
generic/285
generic/312

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>

common/rc

@@ -2190,6 +2190,22 @@ init_rc()
 	export XFS_IO_PROG="$XFS_IO_PROG -F"
 }
 
+# get real device path name by following link
+_real_dev()
+{
+	local _dev=$1
+	if [ -b "$_dev" ] && [ -L "$_dev" ]; then
+		_dev=`readlink -f "$_dev"`
+	fi
+	echo $_dev
+}
+
+# basename of a device
+_short_dev()
+{
+	echo `basename $(_real_dev $1)`
+}
+
 init_rc
 
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