ubifs: 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: Richard Weinberger <[e-mail]>
CC: Artem Bityutskiy <[e-mail]>
CC: Adrian Hunter <[e-mail]>
CC: [e-mail]
Acked-by: Richard Weinberger <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

fs/ubifs/super.c

···
 	}
 
 	ubifs_umount(c);
-	bdi_destroy(&c->bdi);
 	ubi_close_volume(c->ubi);
 	mutex_unlock(&c->umount_mutex);
 }
···
 		goto out;
 	}
 
+	err = ubifs_parse_options(c, data, 0);
+	if (err)
+		goto out_close;
+
 	/*
 	 * UBIFS provides 'backing_dev_info' in order to disable read-ahead. For
 	 * UBIFS, I/O is not deferred, it is done immediately in readpage,
 	 * which means the user would have to wait not just for their own I/O
 	 * but the read-ahead I/O as well i.e. completely pointless.
 	 *
-	 * Read-ahead will be disabled because @c->bdi.ra_pages is 0.
+	 * Read-ahead will be disabled because @sb->s_bdi->ra_pages is 0. Also
+	 * @sb->s_bdi->capabilities are initialized to 0 so there won't be any
+	 * writeback happening.
 	 */
-	c->bdi.name = "ubifs",
-	c->bdi.capabilities = 0;
-	err  = bdi_init(&c->bdi);
+	err = super_setup_bdi_name(sb, "ubifs_%d_%d", c->vi.ubi_num,
+				   c->vi.vol_id);
 	if (err)
 		goto out_close;
-	err = bdi_register(&c->bdi, NULL, "ubifs_%d_%d",
-			   c->vi.ubi_num, c->vi.vol_id);
-	if (err)
-		goto out_bdi;
 
-	err = ubifs_parse_options(c, data, 0);
-	if (err)
-		goto out_bdi;
-
-	sb->s_bdi = &c->bdi;
 	sb->s_fs_info = c;
 	sb->s_magic = UBIFS_SUPER_MAGIC;
 	sb->s_blocksize = UBIFS_BLOCK_SIZE;
···
 	ubifs_umount(c);
 out_unlock:
 	mutex_unlock(&c->umount_mutex);
-out_bdi:
-	bdi_destroy(&c->bdi);
 out_close:
 	ubi_close_volume(c->ubi);
 out:

fs/ubifs/ubifs.h

···
  * struct ubifs_info - UBIFS file-system description data structure
  * (per-superblock).
  * @vfs_sb: VFS @struct super_block object
- * @bdi: backing device info object to make VFS happy and disable read-ahead
  *
  * @highest_inum: highest used inode number
  * @max_sqnum: current global sequence number
···
  */
 struct ubifs_info {
 	struct super_block *vfs_sb;
-	struct backing_dev_info bdi;
 
 	ino_t highest_inum;
 	unsigned long long max_sqnum;
···
 extern const struct file_operations ubifs_dir_operations;
 extern const struct inode_operations ubifs_dir_inode_operations;
 extern const struct inode_operations ubifs_symlink_inode_operations;
-extern struct backing_dev_info ubifs_backing_dev_info;
 extern struct ubifs_compressor *ubifs_compressors[UBIFS_COMPR_TYPES_CNT];
 
 /* io.c */