mm: bdi: expose the BDI object in sysfs for FUSE

Register FUSE's backing_dev_info under sysfs with the name "fuse-MAJOR:MINOR"

Make the fuse control filesystem use s_dev instead of a fuse specific ID.
This makes it easier to match directories under /sys/fs/fuse/connections/ with
directories under /sys/class/bdi, and with actual mounts.

Signed-off-by: Miklos Szeredi <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/fuse/control.c

···
 
 	parent = fuse_control_sb->s_root;
 	inc_nlink(parent->d_inode);
-	sprintf(name, "%llu", (unsigned long long) fc->id);
+	sprintf(name, "%u", fc->dev);
 	parent = fuse_ctl_add_dentry(parent, fc, name, S_IFDIR | 0500, 2,
 				     &simple_dir_inode_operations,
 				     &simple_dir_operations);

fs/fuse/fuse_i.h

···
 	/** Entry on the fuse_conn_list */
 	struct list_head entry;
 
-	/** Unique ID */
-	u64 id;
+	/** Device ID from super block */
+	dev_t dev;
 
 	/** Dentries in the control filesystem */
 	struct dentry *ctl_dentry[FUSE_CTL_NUM_DENTRIES];

fs/fuse/inode.c

···
 	return 0;
 }
 
-static struct fuse_conn *new_conn(void)
+static struct fuse_conn *new_conn(struct super_block *sb)
 {
 	struct fuse_conn *fc;
 	int err;
···
 		atomic_set(&fc->num_waiting, 0);
 		fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
 		fc->bdi.unplug_io_fn = default_unplug_io_fn;
+		fc->dev = sb->s_dev;
 		err = bdi_init(&fc->bdi);
-		if (err) {
-			kfree(fc);
-			fc = NULL;
-			goto out;
-		}
+		if (err)
+			goto error_kfree;
+		err = bdi_register_dev(&fc->bdi, fc->dev);
+		if (err)
+			goto error_bdi_destroy;
 		fc->reqctr = 0;
 		fc->blocked = 1;
 		fc->attr_version = 1;
 		get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
 	}
-out:
 	return fc;
+
+error_bdi_destroy:
+	bdi_destroy(&fc->bdi);
+error_kfree:
+	mutex_destroy(&fc->inst_mutex);
+	kfree(fc);
+	return NULL;
 }
 
 void fuse_conn_put(struct fuse_conn *fc)
···
 	request_send_background(fc, req);
 }
 
-static u64 conn_id(void)
-{
-	static u64 ctr = 1;
-	return ctr++;
-}
-
 static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 {
 	struct fuse_conn *fc;
···
 	if (file->f_op != &fuse_dev_operations)
 		return -EINVAL;
 
-	fc = new_conn();
+	fc = new_conn(sb);
 	if (!fc)
 		return -ENOMEM;
 
···
 	if (file->private_data)
 		goto err_unlock;
 
-	fc->id = conn_id();
 	err = fuse_ctl_add_conn(fc);
 	if (err)
 		goto err_unlock;