dm persistent data: set some btree fn parms const

Mark some constant parameters constant in some dm-btree functions.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-thin-metadata.c

@@ -280,7 +280,7 @@ static void unpack_block_time(uint64_t v, dm_block_t *b, uint32_t *t)
 	*t = v & ((1 << 24) - 1);
 }
 
-static void data_block_inc(void *context, void *value_le)
+static void data_block_inc(void *context, const void *value_le)
 {
 	struct dm_space_map *sm = context;
 	__le64 v_le;
@@ -292,7 +292,7 @@ static void data_block_inc(void *context, void *value_le)
 	dm_sm_inc_block(sm, b);
 }
 
-static void data_block_dec(void *context, void *value_le)
+static void data_block_dec(void *context, const void *value_le)
 {
 	struct dm_space_map *sm = context;
 	__le64 v_le;
@@ -304,7 +304,7 @@ static void data_block_dec(void *context, void *value_le)
 	dm_sm_dec_block(sm, b);
 }
 
-static int data_block_equal(void *context, void *value1_le, void *value2_le)
+static int data_block_equal(void *context, const void *value1_le, const void *value2_le)
 {
 	__le64 v1_le, v2_le;
 	uint64_t b1, b2;
@@ -318,7 +318,7 @@ static int data_block_equal(void *context, void *value1_le, void *value2_le)
 	return b1 == b2;
 }
 
-static void subtree_inc(void *context, void *value)
+static void subtree_inc(void *context, const void *value)
 {
 	struct dm_btree_info *info = context;
 	__le64 root_le;
@@ -329,7 +329,7 @@ static void subtree_inc(void *context, void *value)
 	dm_tm_inc(info->tm, root);
 }
 
-static void subtree_dec(void *context, void *value)
+static void subtree_dec(void *context, const void *value)
 {
 	struct dm_btree_info *info = context;
 	__le64 root_le;
@@ -341,7 +341,7 @@ static void subtree_dec(void *context, void *value)
 		DMERR("btree delete failed\n");
 }
 
-static int subtree_equal(void *context, void *value1_le, void *value2_le)
+static int subtree_equal(void *context, const void *value1_le, const void *value2_le)
 {
 	__le64 v1_le, v2_le;
 	memcpy(&v1_le, value1_le, sizeof(v1_le));

drivers/md/persistent-data/dm-btree.h

@@ -58,21 +58,21 @@ struct dm_btree_value_type {
 	 * somewhere.) This method is _not_ called for insertion of a new
 	 * value: It is assumed the ref count is already 1.
 	 */
-	void (*inc)(void *context, void *value);
+	void (*inc)(void *context, const void *value);
 
 	/*
 	 * This value is being deleted.  The btree takes care of freeing
 	 * the memory pointed to by @value.  Often the del function just
 	 * needs to decrement a reference count somewhere.
 	 */
-	void (*dec)(void *context, void *value);
+	void (*dec)(void *context, const void *value);
 
 	/*
 	 * A test for equality between two values.  When a value is
 	 * overwritten with a new one, the old one has the dec method
 	 * called _unless_ the new and old value are deemed equal.
 	 */
-	int (*equal)(void *context, void *value1, void *value2);
+	int (*equal)(void *context, const void *value1, const void *value2);
 };
 
 /*