linux-kernel - Re: [PATCH 1/2] block: Introduce BIO_ENDIO

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Date:	Wed, 11 Nov 2015 12:54:11 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	Baolin Wang <baolin.wang@...aro.org>
Cc:	axboe@...nel.dk, agk@...hat.com, dm-devel@...hat.com,
	neilb@...e.com, linux-raid@...r.kernel.org, jack@...e.cz,
	arnd@...db.de, linux-kernel@...r.kernel.org, keith.busch@...el.com,
	jmoyer@...hat.com, broonie@...nel.org, tj@...nel.org,
	bart.vanassche@...disk.com, dineshg@...cinc.com
Subject: Re: [PATCH 1/2] block: Introduce BIO_ENDIO_FREE for bio flags

On Wed, Nov 11 2015 at  4:31am -0500,
Baolin Wang <baolin.wang@...aro.org> wrote:

> When we use dm-crypt to decrypt block data, it will decrypt the block data
> in endio() when one IO is completed. In this situation we don't want the
> cloned bios is freed before calling the endio().
> 
> Thus introduce 'BIO_ENDIO_FREE' flag to support the request handling for dm-crypt,
> this flag will ensure that blk layer does not complete the cloned bios before
> completing the request. When the crypt endio is called, post-processsing is
> done and then the dm layer will complete the bios (clones) and free them.

Not following why request-based DM's partial completion handling
(drivers/md/dm.c:end_clone_bio) isn't a sufficient hook -- no need to
add block complexity.

But that aside, I'm not liking the idea of a request-based dm-crypt.

> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index 76d23fa..f636c50 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -407,6 +407,11 @@ union map_info *dm_get_rq_mapinfo(struct request *rq);
>  
>  struct queue_limits *dm_get_queue_limits(struct mapped_device *md);
>  
> +void dm_end_request(struct request *clone, int error);
> +void dm_kill_unmapped_request(struct request *rq, int error);
> +void dm_dispatch_clone_request(struct request *clone, struct request *rq);
> +struct request *dm_get_orig_rq(struct request *clone);
> +
>  /*
>   * Geometry functions.
>   */

I have no interest in seeing any request-based DM interfaces exported.
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