linux-kernel - Re: [RFC PATCH v13 13/20] dm: add finalize hook to target

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Message-ID: <ZeNQFlw74KJ9Spdr@redhat.com>
Date: Sat, 2 Mar 2024 11:13:10 -0500
From: Mike Snitzer <snitzer@...nel.org>
To: Fan Wu <wufan@...ux.microsoft.com>
Cc: corbet@....net, zohar@...ux.ibm.com, jmorris@...ei.org,
	serge@...lyn.com, tytso@....edu, ebiggers@...nel.org,
	axboe@...nel.dk, agk@...hat.com, eparis@...hat.com,
	paul@...l-moore.com, linux-doc@...r.kernel.org,
	linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fscrypt@...r.kernel.org, linux-block@...r.kernel.org,
	dm-devel@...ts.linux.dev, audit@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v13 13/20] dm: add finalize hook to target_type

On Wed, Feb 28 2024 at  7:54P -0500,
Fan Wu <wufan@...ux.microsoft.com> wrote:

> This patch adds a target finalize hook.
> 
> The hook is triggered just before activating an inactive table of a
> mapped device. If it returns an error the __bind get cancelled.
> 
> The dm-verity target will use this hook to attach the dm-verity's
> roothash metadata to the block_device struct of the mapped device.
> 
> Signed-off-by: Fan Wu <wufan@...ux.microsoft.com>
> 
> ---
> v1-v10:
>   + Not present
> 
> v11:
>   + Introduced
> 
> v12:
>   + No changes
> 
> v13:
>   + No changes
> ---
>  drivers/md/dm.c               | 12 ++++++++++++
>  include/linux/device-mapper.h |  7 +++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 8dcabf84d866..15b46edae49f 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -2266,6 +2266,18 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
>  		goto out;
>  	}
>  
> +	for (unsigned int i = 0; i < t->num_targets; i++) {
> +		struct dm_target *ti = dm_table_get_target(t, i);
> +
> +		if (ti->type->finalize) {
> +			ret = ti->type->finalize(ti);
> +			if (ret) {
> +				old_map = ERR_PTR(ret);
> +				goto out;
> +			}
> +		}
> +	}
> +
>  	old_map = rcu_dereference_protected(md->map, lockdep_is_held(&md->suspend_lock));
>  	rcu_assign_pointer(md->map, (void *)t);
>  	md->immutable_target_type = dm_table_get_immutable_target_type(t);
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index 772ab4d74d94..627400b2d9af 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -160,6 +160,12 @@ typedef int (*dm_dax_zero_page_range_fn)(struct dm_target *ti, pgoff_t pgoff,
>   */
>  typedef size_t (*dm_dax_recovery_write_fn)(struct dm_target *ti, pgoff_t pgoff,
>  		void *addr, size_t bytes, struct iov_iter *i);
> +/*
> + * Returns:
> + *  < 0 : error
> + *  = 0 : success
> + */
> +typedef int (*dm_finalize_fn) (struct dm_target *target);

This needs some documentation, e.g.: this hook allows DM targets in an
inactive table to complete their setup before the table is made
active.

Mike

>  
>  void dm_error(const char *message);
>  
> @@ -210,6 +216,7 @@ struct target_type {
>  	dm_dax_direct_access_fn direct_access;
>  	dm_dax_zero_page_range_fn dax_zero_page_range;
>  	dm_dax_recovery_write_fn dax_recovery_write;
> +	dm_finalize_fn finalize;
>  
>  	/* For internal device-mapper use. */
>  	struct list_head list;
> -- 
> 2.43.1
> 
>