linux-kernel - Re: [dm-devel] [PATCH v2] dm ioctl: allow change device target type to error

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Message-ID: <alpine.LRH.2.02.1308211041180.10797@file01.intranet.prod.int.rdu2.redhat.com>
Date:	Wed, 21 Aug 2013 10:48:28 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	device-mapper development <dm-devel@...hat.com>
cc:	Mike Snitzer <snitzer@...hat.com>,
	Alasdair Kergon <agk@...hat.com>, Joe Jin <joe.jin@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [dm-devel] [PATCH v2] dm ioctl: allow change device target type
 to error

On Wed, 21 Aug 2013, Joe Jin wrote:

> commit a5664da "dm ioctl: make bio or request based device type immutable"
> prevented "dmsetup wape_table" change the target type to "error".

That commit a5664da is there for a reason (it is not possible to change 
bio-based device to request-based and vice versa) and I don't really see 
how this patch is supposed to work.

If there are bios that are in flight and that already passed through 
blk_queue_bio, and you change the device from request-based to bio-based, 
what are you going to do with them? - The patch doesn't do anything about 
it.

A better approach would be to create a new request-based target "error-rq" 
and change the multipath target to "error-rq" target. That way, you don't 
have to change device type from request based to bio based.

Mikulas

> -v2: setup md->queue even target type is "error".
> 
> Signed-off-by: Joe Jin <joe.jin@...cle.com>
> ---
>  drivers/md/dm-ioctl.c |  4 ++++
>  drivers/md/dm-table.c | 12 ++++++++++++
>  drivers/md/dm.h       |  1 +
>  3 files changed, 17 insertions(+)
> 
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index f1b7586..2a9b63d 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -1280,6 +1280,9 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
>  		goto out;
>  	}
>  
> +	if (dm_is_error_target(t))
> +		goto error_target;
> +
>  	/* Protect md->type and md->queue against concurrent table loads. */
>  	dm_lock_md_type(md);
>  	if (dm_get_md_type(md) == DM_TYPE_NONE)
> @@ -1293,6 +1296,7 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
>  		goto out;
>  	}
>  
> +error_target:
>  	/* setup md->queue to reflect md's type (may block) */
>  	r = dm_setup_md_queue(md);
>  	if (r) {
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index f221812..27be46a 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -184,6 +184,18 @@ static int alloc_targets(struct dm_table *t, unsigned int num)
>  	return 0;
>  }
>  
> +bool dm_is_error_target(struct dm_table *t)
> +{
> +	unsigned i;
> +
> +	for (i = 0; i < t->num_targets; i++) {
> +		struct dm_target *tgt = t->targets + i;
> +		if (strcmp(tgt->type->name, "error") == 0)
> +			return true;
> +	}
> +	return false;
> +}
> +
>  int dm_table_create(struct dm_table **result, fmode_t mode,
>  		    unsigned num_targets, struct mapped_device *md)
>  {
> diff --git a/drivers/md/dm.h b/drivers/md/dm.h
> index 45b97da..c7bceeb 100644
> --- a/drivers/md/dm.h
> +++ b/drivers/md/dm.h
> @@ -69,6 +69,7 @@ unsigned dm_table_get_type(struct dm_table *t);
>  struct target_type *dm_table_get_immutable_target_type(struct dm_table *t);
>  bool dm_table_request_based(struct dm_table *t);
>  bool dm_table_supports_discards(struct dm_table *t);
> +bool dm_is_error_target(struct dm_table *t);
>  int dm_table_alloc_md_mempools(struct dm_table *t);
>  void dm_table_free_md_mempools(struct dm_table *t);
>  struct dm_md_mempools *dm_table_get_md_mempools(struct dm_table *t);
> -- 
> 1.8.3.1
> 
> --
> dm-devel mailing list
> dm-devel@...hat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
> 
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