btrfs-progs: tests: enhance mkfs option injection

Add support for TEST_ARGS_MKFS to allow injection of eg. checksum
command for the all tests. Use like

 $ make TEST_ARGS_MKFS='--csum=xxhash' TEST_ENABLE_OVERRIDE=true test-mkfs

This affects all mkfs.btrfs commands that are run by run_check and other
helpers, IOW this affects all tests, not just mkfs specific ones.

Signed-off-by: David Sterba <dsterba@suse.com>

tests/README.md

@@ -126,6 +126,9 @@ the root helper).
 * `TEST_ARGS_CHECK` -- user-defined arguments to `btrfs check`, before the
   test-specific arguments
 
+* `TEST_ARGS_MKFS` -- user-defined arguments to `mkfs.btrfs`, before the
+  test-specific arguments
+
 Multiple values can be separated by `,`.
 
 ### Permissions

tests/common

@@ -91,11 +91,19 @@ _get_spec_ins()
 			echo -n 4
 			return
 		fi
+		if [[ $2 =~ /mkfs.btrfs$ ]]; then
+			echo -n 3
+			return
+		fi
 	else
 		if [[ $1 =~ /btrfs$ ]]; then
 			echo -n 3
 			return
 		fi
+		if [[ $1 =~ /mkfs.btrfs$ ]]; then
+			echo -n 2
+			return
+		fi
 	fi
 	echo -n 2
 }
@@ -113,6 +121,7 @@ _cmd_spec()
 		fi
 		case "$1" in
 	  		check) echo -n "$TEST_ARGS_CHECK" ;;
+			*/mkfs.btrfs) echo -n "$TEST_ARGS_MKFS" ;;
 		esac
 	fi
 }
@@ -713,6 +722,7 @@ init_env()
 	if [ "$TEST_ENABLE_OVERRIDE" = 'true' -a -n "$RESULTS" ]; then
 		echo "INCLUDE common.local" >> "$RESULTS"
 		echo "  check: $TEST_ARGS_CHECK" >> "$RESULTS"
+		echo "  mkfs: $TEST_ARGS_MKFS" >> "$RESULTS"
 	fi
 }
 init_env