btrfs: struct-funcs, constify readers

We have reader helpers for most of the on-disk structures that use
an extent_buffer and pointer as offset into the buffer that are
read-only.  We should mark them as const and, in turn, allow consumers
of these interfaces to mark the buffers const as well.

No impact on code, but serves as documentation that a buffer is intended
not to be modified.
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -5405,9 +5405,8 @@ int read_extent_buffer_pages(struct extent_io_tree *tree,
 	return ret;
 }
 
-void read_extent_buffer(struct extent_buffer *eb, void *dstv,
-			unsigned long start,
-			unsigned long len)
+void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
+			unsigned long start, unsigned long len)
 {
 	size_t cur;
 	size_t offset;
@@ -5436,9 +5435,9 @@ void read_extent_buffer(struct extent_buffer *eb, void *dstv,
 	}
 }
 
-int read_extent_buffer_to_user(struct extent_buffer *eb, void __user *dstv,
-			unsigned long start,
-			unsigned long len)
+int read_extent_buffer_to_user(const struct extent_buffer *eb,
+			       void __user *dstv,
+			       unsigned long start, unsigned long len)
 {
 	size_t cur;
 	size_t offset;
@@ -5478,9 +5477,9 @@ int read_extent_buffer_to_user(struct extent_buffer *eb, void __user *dstv,
  * return 1 if the item spans two pages.
  * return -EINVAL otherwise.
  */
-int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
-			       unsigned long min_len, char **map,
-			       unsigned long *map_start,
+int map_private_extent_buffer(const struct extent_buffer *eb,
+			      unsigned long start, unsigned long min_len,
+			      char **map, unsigned long *map_start,
 			      unsigned long *map_len)
 {
 	size_t offset = start & (PAGE_SIZE - 1);
@@ -5515,9 +5514,8 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
 	return 0;
 }
 
-int memcmp_extent_buffer(struct extent_buffer *eb, const void *ptrv,
-			  unsigned long start,
-			  unsigned long len)
+int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
+			 unsigned long start, unsigned long len)
 {
 	size_t cur;
 	size_t offset;

fs/btrfs/extent_io.h

@@ -449,14 +449,13 @@ static inline void extent_buffer_get(struct extent_buffer *eb)
 	atomic_inc(&eb->refs);
 }
 
-int memcmp_extent_buffer(struct extent_buffer *eb, const void *ptrv,
-			  unsigned long start,
-			  unsigned long len);
-void read_extent_buffer(struct extent_buffer *eb, void *dst,
+int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
+			 unsigned long start, unsigned long len);
+void read_extent_buffer(const struct extent_buffer *eb, void *dst,
 			unsigned long start,
 			unsigned long len);
-int read_extent_buffer_to_user(struct extent_buffer *eb, void __user *dst,
-			       unsigned long start,
+int read_extent_buffer_to_user(const struct extent_buffer *eb,
+			       void __user *dst, unsigned long start,
 			       unsigned long len);
 void write_extent_buffer_fsid(struct extent_buffer *eb, const void *src);
 void write_extent_buffer_chunk_tree_uuid(struct extent_buffer *eb,
@@ -486,9 +485,9 @@ void set_extent_buffer_uptodate(struct extent_buffer *eb);
 void clear_extent_buffer_uptodate(struct extent_buffer *eb);
 int extent_buffer_uptodate(struct extent_buffer *eb);
 int extent_buffer_under_io(struct extent_buffer *eb);
-int map_private_extent_buffer(struct extent_buffer *eb, unsigned long offset,
-		      unsigned long min_len, char **map,
-		      unsigned long *map_start,
+int map_private_extent_buffer(const struct extent_buffer *eb,
+			      unsigned long offset, unsigned long min_len,
+			      char **map, unsigned long *map_start,
 			      unsigned long *map_len);
 void extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end);
 void extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end);

fs/btrfs/struct-funcs.c

@@ -50,8 +50,8 @@ static inline void put_unaligned_le8(u8 val, void *p)
  */
 
 #define DEFINE_BTRFS_SETGET_BITS(bits)					\
-u##bits btrfs_get_token_##bits(struct extent_buffer *eb, void *ptr,	\
-			       unsigned long off,			\
+u##bits btrfs_get_token_##bits(const struct extent_buffer *eb,		\
+			       const void *ptr, unsigned long off,	\
 			       struct btrfs_map_token *token)		\
 {									\
 	unsigned long part_offset = (unsigned long)ptr;			\
@@ -90,7 +90,8 @@ u##bits btrfs_get_token_##bits(struct extent_buffer *eb, void *ptr,	\
 	return res;							\
 }									\
 void btrfs_set_token_##bits(struct extent_buffer *eb,			\
-			    void *ptr, unsigned long off, u##bits val,	\
+			    const void *ptr, unsigned long off,		\
+			    u##bits val,				\
 			    struct btrfs_map_token *token)		\
 {									\
 	unsigned long part_offset = (unsigned long)ptr;			\
@@ -133,7 +134,7 @@ DEFINE_BTRFS_SETGET_BITS(16)
 DEFINE_BTRFS_SETGET_BITS(32)
 DEFINE_BTRFS_SETGET_BITS(64)
 
-void btrfs_node_key(struct extent_buffer *eb,
+void btrfs_node_key(const struct extent_buffer *eb,
 		    struct btrfs_disk_key *disk_key, int nr)
 {
 	unsigned long ptr = btrfs_node_key_ptr_offset(nr);