[dm-devel] [PATCH 43/44] block: merge struct block_device and struct hd_struct

[Jan Kara]

On Thu 26-11-20 14:04:21, Christoph Hellwig wrote:
> Instead of having two structures that represent each block device with
> different life time rules, merge them into a single one.  This also
> greatly simplifies the reference counting rules, as we can use the inode
> reference count as the main reference count for the new struct
> block_device, with the device model reference front ending it for device
> model interaction.  The percpu refcount in struct hd_struct is entirely
> gone given that struct block_device must be opened and thus valid for
> the duration of the I/O.

The percpu refcount is long gone after the series refactoring...

> @@ -939,13 +910,13 @@ void blk_request_module(dev_t devt)
>   */
>  struct block_device *bdget_disk(struct gendisk *disk, int partno)
>  {
> -	struct hd_struct *part;
>  	struct block_device *bdev = NULL;
>  
> -	part = disk_get_part(disk, partno);
> -	if (part)
> -		bdev = bdget_part(part);
> -	disk_put_part(part);
> +	rcu_read_lock();
> +	bdev = __disk_get_part(disk, partno);
> +	if (bdev)
> +		bdgrab(bdev);

Again I think you need to accommodate for bdgrab() returning NULL here when
we race with partition destruction...

> +	rcu_read_unlock();
>  
>  	return bdev;
>  }

								Honza
-- 
Jan Kara <jack at suse.com>
SUSE Labs, CR