Re: [PATCH 65/78] dm: remove the block_device reference in struct mapped_device

[Hannes Reinecke <hare@suse.de>]

On 11/16/20 3:57 PM, Christoph Hellwig wrote:
> Get rid of the long-lasting struct block_device reference in
> struct mapped_device.  The only remaining user is the freeze code,
> where we can trivially look up the block device at freeze time
> and release the reference at thaw time.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/md/dm-core.h |  2 --
>   drivers/md/dm.c      | 22 +++++++++++-----------
>   2 files changed, 11 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
> index d522093cb39dda..b1b400ed76fe90 100644
> --- a/drivers/md/dm-core.h
> +++ b/drivers/md/dm-core.h
> @@ -107,8 +107,6 @@ struct mapped_device {
>   	/* kobject and completion */
>   	struct dm_kobject_holder kobj_holder;
>   
> -	struct block_device *bdev;
> -
>   	struct dm_stats stats;
>   
>   	/* for blk-mq request-based DM support */
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 6d7eb72d41f9ea..c789ffea2badde 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1744,11 +1744,6 @@ static void cleanup_mapped_device(struct mapped_device *md)
>   
>   	cleanup_srcu_struct(&md->io_barrier);
>   
> -	if (md->bdev) {
> -		bdput(md->bdev);
> -		md->bdev = NULL;
> -	}
> -
>   	mutex_destroy(&md->suspend_lock);
>   	mutex_destroy(&md->type_lock);
>   	mutex_destroy(&md->table_devices_lock);
> @@ -1840,10 +1835,6 @@ static struct mapped_device *alloc_dev(int minor)
>   	if (!md->wq)
>   		goto bad;
>   
> -	md->bdev = bdget_disk(md->disk, 0);
> -	if (!md->bdev)
> -		goto bad;
> -
>   	dm_stats_init(&md->stats);
>   
>   	/* Populate the mapping, nobody knows we exist yet */
> @@ -2384,12 +2375,17 @@ struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
>    */
>   static int lock_fs(struct mapped_device *md)
>   {
> +	struct block_device *bdev;
>   	int r;
>   
>   	WARN_ON(md->frozen_sb);
>   
> -	md->frozen_sb = freeze_bdev(md->bdev);
> +	bdev = bdget_disk(md->disk, 0);
> +	if (!bdev)
> +		return -ENOMEM;
> +	md->frozen_sb = freeze_bdev(bdev);
>   	if (IS_ERR(md->frozen_sb)) {
> +		bdput(bdev);
>   		r = PTR_ERR(md->frozen_sb);
>   		md->frozen_sb = NULL;
>   		return r;
> @@ -2402,10 +2398,14 @@ static int lock_fs(struct mapped_device *md)
>   
>   static void unlock_fs(struct mapped_device *md)
>   {
> +	struct block_device *bdev;
> +
>   	if (!test_bit(DMF_FROZEN, &md->flags))
>   		return;
>   
> -	thaw_bdev(md->bdev, md->frozen_sb);
> +	bdev = md->frozen_sb->s_bdev;
> +	thaw_bdev(bdev, md->frozen_sb);
> +	bdput(bdev);
>   	md->frozen_sb = NULL;
>   	clear_bit(DMF_FROZEN, &md->flags);
>   }
Yay. Just what I need for the blk-interposer code, where the ->bdev
pointer is really getting in the way.

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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