exofs: Convert to separately allocated bdi

Allocate struct backing_dev_info separately instead of embedding it
inside the superblock. This unifies handling of bdi among users.

CC: Boaz Harrosh <[e-mail]>
CC: Benny Halevy <[e-mail]>
Acked-by: Boaz Harrosh <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

fs/exofs/exofs.h

···
  * our extension to the in-memory superblock
  */
 struct exofs_sb_info {
-	struct backing_dev_info bdi;		/* register our bdi with VFS  */
 	struct exofs_sb_stats s_ess;		/* Written often, pre-allocate*/
 	int		s_timeout;		/* timeout for OSD operations */
 	uint64_t	s_nextid;		/* highest object ID used     */

fs/exofs/super.c

···
 			    sbi->one_comp.obj.partition);
 
 	exofs_sysfs_sb_del(sbi);
-	bdi_destroy(&sbi->bdi);
 	exofs_free_sbi(sbi);
 	sb->s_fs_info = NULL;
 }
···
 	__sbi_read_stats(sbi);
 
 	/* set up operation vectors */
-	sbi->bdi.ra_pages = __ra_pages(&sbi->layout);
-	sb->s_bdi = &sbi->bdi;
+	ret = super_setup_bdi(sb);
+	if (ret) {
+		EXOFS_DBGMSG("Failed to super_setup_bdi\n");
+		goto free_sbi;
+	}
+	sb->s_bdi->ra_pages = __ra_pages(&sbi->layout);
 	sb->s_fs_info = sbi;
 	sb->s_op = &exofs_sops;
 	sb->s_export_op = &exofs_export_ops;
···
 		EXOFS_ERR("ERROR: corrupt root inode (mode = %hd)\n",
 		       root->i_mode);
 		ret = -EINVAL;
-		goto free_sbi;
-	}
-
-	ret = bdi_setup_and_register(&sbi->bdi, "exofs");
-	if (ret) {
-		EXOFS_DBGMSG("Failed to bdi_setup_and_register\n");
-		dput(sb->s_root);
-		sb->s_root = NULL;
 		goto free_sbi;
 	}