Re: [PATCH v4 02/10] scsi: scsi_debug: Make atomic writes and ZBC emulation mutually exclusive

[John Garry <john.garry@linux.dev>]

On 9/18/26 07:29, Niklas Cassel wrote:
> There are no SMR drives that support atomic writes. Emulating a device
> that supports both is emulating something that a user cannot encounter,
> rather than the drives that exist, and it means maintaining the zone
> handling of a command that no zoned device implements.
> 
> Nothing in the standards forbids the combination. For what would be by
> far the most common case, a host managed SMR drive whose logical block
> size equals its physical block size, there is no problem in the two
> features being combined: the drive vendor only has to give atomic
> writes an alignment that makes sense with regards to ZBC, for instance
> equal to the physical block size. This is therefore a choice not to
> complicate scsi_debug, rather than a restriction that the standards
> impose.
> 
> Refuse the combination at initialisation. If SMR drives that support
> atomic writes ever become a thing, this can be changed back.
> 
> Suggested-by: Damien Le Moal <dlemoal@kernel.org>
> Assisted-by: LLM
> Signed-off-by: Niklas Cassel <cassel@kernel.org>

Reviewed-by: John Garry <john.garry@linux.dev>

> ---
> Tested by loading the module with each combination:
> 
>    zbc=managed atomic_wr=1    refused, -EINVAL
>    zbc=aware   atomic_wr=1    refused, -EINVAL
>    zbc=managed                loads
>    atomic_wr=1                loads
> ---
>   drivers/scsi/scsi_debug.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index c664966e95cb..8e45a57ae406 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -8739,6 +8739,11 @@ static int __init scsi_debug_init(void)
>   		return -EINVAL;
>   	}
>   
> +	if (sdeb_zbc_in_use && sdebug_atomic_wr) {
> +		pr_err("atomic_wr is not supported by a zoned device\n");
> +		return -EINVAL;
> +	}
> +
>   	if (sdebug_dev_size_mb == DEF_DEV_SIZE_PRE_INIT)
>   		sdebug_dev_size_mb = DEF_DEV_SIZE_MB;
>   	if (sdebug_dev_size_mb < 1)