btrfs: constify structs with op functions or static definitions

There are some op tables that can be easily made const, similarly the
sysfs feature and raid tables. This is motivated by PaX CONSTIFY plugin.
Signed-off-by: NDavid Sterba <dsterba@suse.cz>

fs/btrfs/compression.c

@@ -750,7 +750,7 @@ static int comp_num_workspace[BTRFS_COMPRESS_TYPES];
 static atomic_t comp_alloc_workspace[BTRFS_COMPRESS_TYPES];
 static wait_queue_head_t comp_workspace_wait[BTRFS_COMPRESS_TYPES];
 
-static struct btrfs_compress_op *btrfs_compress_op[] = {
+static const struct btrfs_compress_op * const btrfs_compress_op[] = {
 	&btrfs_zlib_compress,
 	&btrfs_lzo_compress,
 };

fs/btrfs/compression.h

@@ -77,7 +77,7 @@ struct btrfs_compress_op {
 			  size_t srclen, size_t destlen);
 };
 
-extern struct btrfs_compress_op btrfs_zlib_compress;
-extern struct btrfs_compress_op btrfs_lzo_compress;
+extern const struct btrfs_compress_op btrfs_zlib_compress;
+extern const struct btrfs_compress_op btrfs_lzo_compress;
 
 #endif

fs/btrfs/disk-io.c

@@ -54,7 +54,7 @@
 #include <asm/cpufeature.h>
 #endif
 
-static struct extent_io_ops btree_extent_io_ops;
+static const struct extent_io_ops btree_extent_io_ops;
 static void end_workqueue_fn(struct btrfs_work *work);
 static void free_fs_root(struct btrfs_root *root);
 static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
@@ -4287,7 +4287,7 @@ static int btrfs_cleanup_transaction(struct btrfs_root *root)
 	return 0;
 }
 
-static struct extent_io_ops btree_extent_io_ops = {
+static const struct extent_io_ops btree_extent_io_ops = {
 	.readpage_end_io_hook = btree_readpage_end_io_hook,
 	.readpage_io_failed_hook = btree_io_failed_hook,
 	.submit_bio_hook = btree_submit_bio_hook,

fs/btrfs/extent_io.h

@@ -97,7 +97,7 @@ struct extent_io_tree {
 	u64 dirty_bytes;
 	int track_uptodate;
 	spinlock_t lock;
-	struct extent_io_ops *ops;
+	const struct extent_io_ops *ops;
 };
 
 struct extent_state {

fs/btrfs/lzo.c

@@ -434,7 +434,7 @@ static int lzo_decompress(struct list_head *ws, unsigned char *data_in,
 	return ret;
 }
 
-struct btrfs_compress_op btrfs_lzo_compress = {
+const struct btrfs_compress_op btrfs_lzo_compress = {
 	.alloc_workspace	= lzo_alloc_workspace,
 	.free_workspace		= lzo_free_workspace,
 	.compress_pages		= lzo_compress_pages,

fs/btrfs/props.c

@@ -425,3 +425,5 @@ static const char *prop_compression_extract(struct inode *inode)
 
 	return NULL;
 }
+
+

fs/btrfs/sysfs.c

@@ -459,7 +459,7 @@ static inline struct btrfs_fs_info *to_fs_info(struct kobject *kobj)
 static char btrfs_unknown_feature_names[3][NUM_FEATURE_BITS][13];
 static struct btrfs_feature_attr btrfs_feature_attrs[3][NUM_FEATURE_BITS];
 
-static u64 supported_feature_masks[3] = {
+static const u64 supported_feature_masks[3] = {
 	[FEAT_COMPAT]    = BTRFS_FEATURE_COMPAT_SUPP,
 	[FEAT_COMPAT_RO] = BTRFS_FEATURE_COMPAT_RO_SUPP,
 	[FEAT_INCOMPAT]  = BTRFS_FEATURE_INCOMPAT_SUPP,

fs/btrfs/transaction.c

@@ -35,7 +35,7 @@
 
 #define BTRFS_ROOT_TRANS_TAG 0
 
-static unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {
+static const unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {
 	[TRANS_STATE_RUNNING]		= 0U,
 	[TRANS_STATE_BLOCKED]		= (__TRANS_USERSPACE |
 					   __TRANS_START),

fs/btrfs/volumes.c

@@ -4131,7 +4131,7 @@ static int btrfs_cmp_device_info(const void *a, const void *b)
 	return 0;
 }
 
-static struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = {
+static const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = {
 	[BTRFS_RAID_RAID10] = {
 		.sub_stripes	= 2,
 		.dev_stripes	= 1,

fs/btrfs/zlib.c

@@ -403,7 +403,7 @@ static int zlib_decompress(struct list_head *ws, unsigned char *data_in,
 	return ret;
 }
 
-struct btrfs_compress_op btrfs_zlib_compress = {
+const struct btrfs_compress_op btrfs_zlib_compress = {
 	.alloc_workspace	= zlib_alloc_workspace,
 	.free_workspace		= zlib_free_workspace,
 	.compress_pages		= zlib_compress_pages,