btrfs: constify and cleanup variables in comparators

Comparators just read the data and thus get const parameters. This
should be also preserved by the local variables, update all comparators
passed to sort or bsearch.

Cleanups:

- unnecessary casts are dropped
- btrfs_cmp_device_free_bytes is cleaned up to follow the common pattern
  and 'inline' is dropped as the function address is taken
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/raid56.c

@@ -1636,9 +1636,9 @@ struct btrfs_plug_cb {
 static int plug_cmp(void *priv, const struct list_head *a,
 		    const struct list_head *b)
 {
-	struct btrfs_raid_bio *ra = container_of(a, struct btrfs_raid_bio,
+	const struct btrfs_raid_bio *ra = container_of(a, struct btrfs_raid_bio,
 						       plug_list);
-	struct btrfs_raid_bio *rb = container_of(b, struct btrfs_raid_bio,
+	const struct btrfs_raid_bio *rb = container_of(b, struct btrfs_raid_bio,
 						       plug_list);
 	u64 a_sector = ra->bio_list.head->bi_iter.bi_sector;
 	u64 b_sector = rb->bio_list.head->bi_iter.bi_sector;

fs/btrfs/send.c

@@ -1198,7 +1198,7 @@ struct backref_ctx {
 static int __clone_root_cmp_bsearch(const void *key, const void *elt)
 {
 	u64 root = (u64)(uintptr_t)key;
-	struct clone_root *cr = (struct clone_root *)elt;
+	const struct clone_root *cr = elt;
 
 	if (root < cr->root->root_key.objectid)
 		return -1;
@@ -1209,8 +1209,8 @@ static int __clone_root_cmp_bsearch(const void *key, const void *elt)
 
 static int __clone_root_cmp_sort(const void *e1, const void *e2)
 {
-	struct clone_root *cr1 = (struct clone_root *)e1;
-	struct clone_root *cr2 = (struct clone_root *)e2;
+	const struct clone_root *cr1 = e1;
+	const struct clone_root *cr2 = e2;
 
 	if (cr1->root->root_key.objectid < cr2->root->root_key.objectid)
 		return -1;

fs/btrfs/super.c

@@ -2096,16 +2096,15 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 }
 
 /* Used to sort the devices by max_avail(descending sort) */
-static inline int btrfs_cmp_device_free_bytes(const void *dev_info1,
-				       const void *dev_info2)
+static int btrfs_cmp_device_free_bytes(const void *a, const void *b)
 {
-	if (((struct btrfs_device_info *)dev_info1)->max_avail >
-	    ((struct btrfs_device_info *)dev_info2)->max_avail)
+	const struct btrfs_device_info *dev_info1 = a;
+	const struct btrfs_device_info *dev_info2 = b;
+
+	if (dev_info1->max_avail > dev_info2->max_avail)
 		return -1;
-	else if (((struct btrfs_device_info *)dev_info1)->max_avail <
-		 ((struct btrfs_device_info *)dev_info2)->max_avail)
+	else if (dev_info1->max_avail < dev_info2->max_avail)
 		return 1;
-	else
 	return 0;
 }
 

fs/btrfs/tree-log.c

@@ -4191,7 +4191,7 @@ static noinline int copy_items(struct btrfs_trans_handle *trans,
 static int extent_cmp(void *priv, const struct list_head *a,
 		      const struct list_head *b)
 {
-	struct extent_map *em1, *em2;
+	const struct extent_map *em1, *em2;
 
 	em1 = list_entry(a, struct extent_map, list);
 	em2 = list_entry(b, struct extent_map, list);

fs/btrfs/volumes.c

@@ -1216,7 +1216,7 @@ static int open_fs_devices(struct btrfs_fs_devices *fs_devices,
 static int devid_cmp(void *priv, const struct list_head *a,
 		     const struct list_head *b)
 {
-	struct btrfs_device *dev1, *dev2;
+	const struct btrfs_device *dev1, *dev2;
 
 	dev1 = list_entry(a, struct btrfs_device, dev_list);
 	dev2 = list_entry(b, struct btrfs_device, dev_list);