[dm-devel] [PATCH v2] dm-zero, dm-error: support discards

[Milan Broz]

On 3/7/23 18:32, Mikulas Patocka wrote:
> dm-zero, dm-error: support discards
> 
> This patch adds discard support to dm-zero and dm-error. dm-zero ignores
> the discards, dm-error return -EIO. It is useful when the user combines
> dm-zero or dm-error with other discard-supporting targets in the same
> table; without dm-zero or dm-error support, discards would be disabled for
> the whole combined device.
> 
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

For the v2 (including the error target):

Tested-by: Milan Broz <gmazyland at gmail.com>

But I would better split it to two patches (per target).

And as kabi mentioned elsewhere - I understand it the way that discards
should fail for error target, as it can be in somewhere down the stack
just write of zeroes (so the patch is IMO correct).

Milan

> 
> ---
>   drivers/md/dm-table.c  |    6 +++++-
>   drivers/md/dm-target.c |   11 ++++++++++-
>   drivers/md/dm-zero.c   |   12 +++++++++++-
>   3 files changed, 26 insertions(+), 3 deletions(-)
> 
> Index: linux-2.6/drivers/md/dm-zero.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-zero.c
> +++ linux-2.6/drivers/md/dm-zero.c
> @@ -27,6 +27,7 @@ static int zero_ctr(struct dm_target *ti
>   	 * Silently drop discards, avoiding -EOPNOTSUPP.
>   	 */
>   	ti->num_discard_bios = 1;
> +	ti->discards_supported = true;
>   
>   	return 0;
>   }
> @@ -45,6 +46,7 @@ static int zero_map(struct dm_target *ti
>   		zero_fill_bio(bio);
>   		break;
>   	case REQ_OP_WRITE:
> +	case REQ_OP_DISCARD:
>   		/* writes get silently dropped */
>   		break;
>   	default:
> @@ -57,13 +59,21 @@ static int zero_map(struct dm_target *ti
>   	return DM_MAPIO_SUBMITTED;
>   }
>   
> +static void zero_io_hints(struct dm_target *ti, struct queue_limits *limits)
> +{
> +	limits->max_discard_sectors = UINT_MAX;
> +	limits->max_hw_discard_sectors = UINT_MAX;
> +	limits->discard_granularity = 512;
> +}
> +
>   static struct target_type zero_target = {
>   	.name   = "zero",
> -	.version = {1, 1, 0},
> +	.version = {1, 2, 0},
>   	.features = DM_TARGET_NOWAIT,
>   	.module = THIS_MODULE,
>   	.ctr    = zero_ctr,
>   	.map    = zero_map,
> +	.io_hints = zero_io_hints,
>   };
>   
>   static int __init dm_zero_init(void)
> Index: linux-2.6/drivers/md/dm-table.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-table.c
> +++ linux-2.6/drivers/md/dm-table.c
> @@ -1670,8 +1670,12 @@ int dm_calculate_queue_limits(struct dm_
>   
>   		blk_set_stacking_limits(&ti_limits);
>   
> -		if (!ti->type->iterate_devices)
> +		if (!ti->type->iterate_devices) {
> +			/* Set I/O hints portion of queue limits */
> +			if (ti->type->io_hints)
> +				ti->type->io_hints(ti, &ti_limits);
>   			goto combine_limits;
> +		}
>   
>   		/*
>   		 * Combine queue limits of all the devices this target uses.
> Index: linux-2.6/drivers/md/dm-target.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-target.c
> +++ linux-2.6/drivers/md/dm-target.c
> @@ -119,6 +119,7 @@ static int io_err_ctr(struct dm_target *
>   	 * Return error for discards instead of -EOPNOTSUPP
>   	 */
>   	tt->num_discard_bios = 1;
> +	tt->discards_supported = true;
>   
>   	return 0;
>   }
> @@ -145,6 +146,13 @@ static void io_err_release_clone_rq(stru
>   {
>   }
>   
> +static void io_err_io_hints(struct dm_target *ti, struct queue_limits *limits)
> +{
> +	limits->max_discard_sectors = UINT_MAX;
> +	limits->max_hw_discard_sectors = UINT_MAX;
> +	limits->discard_granularity = 512;
> +}
> +
>   static long io_err_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
>   		long nr_pages, enum dax_access_mode mode, void **kaddr,
>   		pfn_t *pfn)
> @@ -154,13 +162,14 @@ static long io_err_dax_direct_access(str
>   
>   static struct target_type error_target = {
>   	.name = "error",
> -	.version = {1, 5, 0},
> +	.version = {1, 6, 0},
>   	.features = DM_TARGET_WILDCARD,
>   	.ctr  = io_err_ctr,
>   	.dtr  = io_err_dtr,
>   	.map  = io_err_map,
>   	.clone_and_map_rq = io_err_clone_and_map_rq,
>   	.release_clone_rq = io_err_release_clone_rq,
> +	.io_hints = io_err_io_hints,
>   	.direct_access = io_err_dax_direct_access,
>   };
>   
>