btrfs/124: add balance --full-balance option

btrfs balance needs --full-balance option since 4.6, so check the
version and then use it.

As this may be useful for other btrfs tests as well, so this patch
also adds _run_btrfs_balance_start() to the common/btrfs file.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

common/btrfs

@@ -356,3 +356,14 @@ _btrfs_compression_algos()
 		echo "${feature#/sys/fs/btrfs/features/compress_}"
 	done
 }
+
+# run btrfs balance start with required --full-balance if available.
+_run_btrfs_balance_start()
+{
+	local bal_opt=""
+
+	$BTRFS_UTIL_PROG balance start --help | grep -q "full-balance"
+	(( $? == 0 )) && bal_opt="--full-balance"
+
+	run_check $BTRFS_UTIL_PROG balance start $bal_opt $*
+}

tests/btrfs/124

@@ -129,7 +129,7 @@ _run_btrfs_util_prog device scan
 _scratch_mount >> $seqres.full 2>&1
 _run_btrfs_util_prog filesystem show
 echo >> $seqres.full
-_run_btrfs_util_prog balance start ${SCRATCH_MNT}
+_run_btrfs_balance_start ${SCRATCH_MNT}
 
 checkpoint2=`md5sum $SCRATCH_MNT/tf2`
 echo $checkpoint2 >> $seqres.full 2>&1