btrfs: constify input buffer parameter in compression code

The input buffers passed down to compression must never be changed,
switch type to u8 as it's a raw byte buffer and use const.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -119,7 +119,7 @@ static int compression_decompress_bio(struct list_head *ws,
 }
 
 static int compression_decompress(int type, struct list_head *ws,
-               unsigned char *data_in, struct page *dest_page,
+               const u8 *data_in, struct page *dest_page,
                unsigned long start_byte, size_t srclen, size_t destlen)
 {
 	switch (type) {
@@ -1232,7 +1232,7 @@ static int btrfs_decompress_bio(struct compressed_bio *cb)
  * single page, and we want to read a single page out of it.
  * start_byte tells us the offset into the compressed data we're interested in
  */
-int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
+int btrfs_decompress(int type, const u8 *data_in, struct page *dest_page,
 		     unsigned long start_byte, size_t srclen, size_t destlen)
 {
 	struct list_head *workspace;

fs/btrfs/compression.h

@@ -86,7 +86,7 @@ int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping,
 			 unsigned long *out_pages,
 			 unsigned long *total_in,
 			 unsigned long *total_out);
-int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
+int btrfs_decompress(int type, const u8 *data_in, struct page *dest_page,
 		     unsigned long start_byte, size_t srclen, size_t destlen);
 int btrfs_decompress_buf2page(const char *buf, u32 buf_len,
 			      struct compressed_bio *cb, u32 decompressed);
@@ -150,7 +150,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
 		u64 start, struct page **pages, unsigned long *out_pages,
 		unsigned long *total_in, unsigned long *total_out);
 int zlib_decompress_bio(struct list_head *ws, struct compressed_bio *cb);
-int zlib_decompress(struct list_head *ws, unsigned char *data_in,
+int zlib_decompress(struct list_head *ws, const u8 *data_in,
 		struct page *dest_page, unsigned long start_byte, size_t srclen,
 		size_t destlen);
 struct list_head *zlib_alloc_workspace(unsigned int level);
@@ -161,7 +161,7 @@ int lzo_compress_pages(struct list_head *ws, struct address_space *mapping,
 		u64 start, struct page **pages, unsigned long *out_pages,
 		unsigned long *total_in, unsigned long *total_out);
 int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb);
-int lzo_decompress(struct list_head *ws, unsigned char *data_in,
+int lzo_decompress(struct list_head *ws, const u8 *data_in,
 		struct page *dest_page, unsigned long start_byte, size_t srclen,
 		size_t destlen);
 struct list_head *lzo_alloc_workspace(unsigned int level);
@@ -171,7 +171,7 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 		u64 start, struct page **pages, unsigned long *out_pages,
 		unsigned long *total_in, unsigned long *total_out);
 int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb);
-int zstd_decompress(struct list_head *ws, unsigned char *data_in,
+int zstd_decompress(struct list_head *ws, const u8 *data_in,
 		struct page *dest_page, unsigned long start_byte, size_t srclen,
 		size_t destlen);
 void zstd_init_workspace_manager(void);

fs/btrfs/lzo.c

@@ -427,7 +427,7 @@ int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
 	return ret;
 }
 
-int lzo_decompress(struct list_head *ws, unsigned char *data_in,
+int lzo_decompress(struct list_head *ws, const u8 *data_in,
 		struct page *dest_page, unsigned long start_byte, size_t srclen,
 		size_t destlen)
 {

fs/btrfs/zlib.c

@@ -355,7 +355,7 @@ int zlib_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
 	return ret;
 }
 
-int zlib_decompress(struct list_head *ws, unsigned char *data_in,
+int zlib_decompress(struct list_head *ws, const u8 *data_in,
 		struct page *dest_page, unsigned long start_byte, size_t srclen,
 		size_t destlen)
 {

fs/btrfs/zstd.c

@@ -616,7 +616,7 @@ int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
 	return ret;
 }
 
-int zstd_decompress(struct list_head *ws, unsigned char *data_in,
+int zstd_decompress(struct list_head *ws, const u8 *data_in,
 		struct page *dest_page, unsigned long start_byte, size_t srclen,
 		size_t destlen)
 {