btrfs: use a single switch statement when initializing delayed ref head

At init_delayed_ref_head(), we are using two separate if statements to
check the delayed ref head action, and initializing 'must_insert_reserved'
to false twice, once when the variable is declared and once again in an
else branch.

Make this simpler and more straightforward by having a single switch
statement, also moving the comment about a drop action to the
corresponding switch case to make it more clear and eliminating the
duplicated initialization of 'must_insert_reserved' to false.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/delayed-ref.c

@@ -702,29 +702,33 @@ static void init_delayed_ref_head(struct btrfs_delayed_ref_head *head_ref,
 	/* If reserved is provided, it must be a data extent. */
 	BUG_ON(!is_data && reserved);
 
+	switch (action) {
+	case BTRFS_UPDATE_DELAYED_HEAD:
+		count_mod = 0;
+		break;
+	case BTRFS_DROP_DELAYED_REF:
 		/*
 		 * The head node stores the sum of all the mods, so dropping a ref
 		 * should drop the sum in the head node by one.
 		 */
-	if (action == BTRFS_UPDATE_DELAYED_HEAD)
-		count_mod = 0;
-	else if (action == BTRFS_DROP_DELAYED_REF)
 		count_mod = -1;
-
+		break;
+	case BTRFS_ADD_DELAYED_EXTENT:
 		/*
-	 * BTRFS_ADD_DELAYED_EXTENT means that we need to update the reserved
-	 * accounting when the extent is finally added, or if a later
-	 * modification deletes the delayed ref without ever inserting the
-	 * extent into the extent allocation tree.  ref->must_insert_reserved
-	 * is the flag used to record that accounting mods are required.
+		 * BTRFS_ADD_DELAYED_EXTENT means that we need to update the
+		 * reserved accounting when the extent is finally added, or if a
+		 * later modification deletes the delayed ref without ever
+		 * inserting the extent into the extent allocation tree.
+		 * ref->must_insert_reserved is the flag used to record that
+		 * accounting mods are required.
 		 *
 		 * Once we record must_insert_reserved, switch the action to
-	 * BTRFS_ADD_DELAYED_REF because other special casing is not required.
+		 * BTRFS_ADD_DELAYED_REF because other special casing is not
+		 * required.
 		 */
-	if (action == BTRFS_ADD_DELAYED_EXTENT)
 		must_insert_reserved = true;
-	else
-		must_insert_reserved = false;
+		break;
+	}
 
 	refcount_set(&head_ref->refs, 1);
 	head_ref->bytenr = bytenr;