Re: [PATCH 0/4] dm: zoned block device fixes

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Mike,

On 5/31/17 05:20, Mike Snitzer wrote:
> On Mon, May 29 2017 at  6:23P -0400,
> Damien Le Moal <damien.lemoal@xxxxxxx> wrote:
> 
>> Mike,
>>
>> The first 3 patches of this series are incremental fixes for the zoned block
>> device support patches that you committed to the for-4.13/dm branch.
>>
>> The first patch correct the zone alignement checks so that the check is
>> performed for any device, regardless of the device LBA size (it is skipped for
>> 512B LBA devices otherwise).
> 
> I folded this first patch into the original commit (baf844bf4ae3).

Great. Thanks.

>> The second patch is a fix for commit baf844bf4ae3 "dm table: add zoned block
>> devices validation". In that commit, the stacked limits zoned model was not
>> set to the zoned model of the table target devices, leading to the exposed
>> device always being exposed as a regular block device. With this fix, dm-flaky
>> and dm-linear work fine on top of host-managed zoned block devices.
>>
>> The third patch fixes zoned model validation again to allow for target types
>> emulating a different zoned model than the model of the table target devices,
>> e.g. dm-zoned.
> 
> The 2nd and 3rd seem over-done to me.  After spending more time than
> ideal, the following patch would seem to be the equivalent to what
> you've done in patches 2 and 3 (sans the "cleanup" of passing limits to
> validate_hardware_zoned_model):
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 6545150..a39bcd9 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1523,19 +1524,39 @@ int dm_calculate_queue_limits(struct dm_table *table,
>  			       dm_device_name(table->md),
>  			       (unsigned long long) ti->begin,
>  			       (unsigned long long) ti->len);
> +
> +		/*
> +		 * FIXME: this should likely be moved to blk_stack_limits(), would
> +		 * also eliminate limits->zoned stacking hack in dm_set_device_limits()
> +		 */
> +		if (limits->zoned == BLK_ZONED_NONE && ti_limits.zoned != BLK_ZONED_NONE) {
> +			/*
> +			 * By default, the stacked limits zoned model is set to
> +			 * BLK_ZONED_NONE in blk_set_stacking_limits(). Update
> +			 * this model using the first target model reported
> +			 * that is not BLK_ZONED_NONE. This will be either the
> +			 * first target device zoned model or the model reported
> +			 * by the target .io_hints.
> +			 */
> +			limits->zoned = ti_limits.zoned;
> +		}
>  	}
>  
>  	/*
>  	 * Verify that the zoned model and zone sectors, as determined before
>  	 * any .io_hints override, are the same across all devices in the table.
> -	 * - but if limits->zoned is not BLK_ZONED_NONE validate match for it
> -	 * - simillarly, check all devices conform to limits->chunk_sectors if
> -	 *   .io_hints altered them
> +	 * - this is especially relevant if .io_hints is emulating a disk-managed
> +	 *   zoned model (aka BLK_ZONED_NONE) on host-managed zoned block devices.
> +	 * BUT...
>  	 */
> -	if (limits->zoned != BLK_ZONED_NONE)
> +	if (limits->zoned != BLK_ZONED_NONE) {
> +		/*
> +		 * ...IF the above limits stacking determined a zoned model
> +		 * validate that all of the table's devices conform to it.
> +		 */
>  		zoned_model = limits->zoned;
> -	if (limits->chunk_sectors != zone_sectors)
>  		zone_sectors = limits->chunk_sectors;
> +	}
>  	if (validate_hardware_zoned_model(table, zoned_model, zone_sectors))
>  		return -EINVAL;
>  
> Anyway, I've folded this into the original commit too.  If you could
> verify it works with your scenarios I'd appreciate it.

I tested with dm-linear, dm-flakey and dm-zoned. No problems detected,
the end device zone model and zone size was always correct. I also tried
all invalid setup I could generate and all were properly caught.

There is however one case that will not work: an HM (or HA) emulating
target on top of a regular (NONE) block device. In that case, we will
end up checking that the underlying devices are compatible HM/HA, whih
will fail. But since none of the existing targets currently do this, I
guess the code is OK as is. What do you think ?

> FYI, any additional cosmetic cleanup can wait (I happen to think this
> code is clearer than how you relied on the matches functions to
> initialize a temporary value).

OK. No problem.

> I also folded in an validate_hardware_zoned_model() optimization to
> return early if zoned_model == BLK_ZONED_NONE, please see/test the
> rolled-up end result here:
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-4.13/dm&id=9a6b54360f147c2d25fba7debc31a3251b804cc2
> 
> Also, please note that I've forcibly rebased linux-dm.git's
> 'for-4.13/dm' and staged it in 'for-next'.

I tested this tree unmodified. No problem detected.
Thank you.

Best regards.

-- 
Damien Le Moal,
Western Digital Research

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