[PATCH v4 01/10] scsi: scsi_debug: Refuse a zoned device with a non-zero lowest aligned LBA

[Niklas Cassel <cassel@kernel.org>]

The LOWEST ALIGNED LOGICAL BLOCK ADDRESS field indicates the LBA of the
first logical block that is located at the beginning of a physical
block, see SBC-6 r02 (T10/BSR INCITS 587), 5.20.2. scsi_debug reports
the lowest_aligned module parameter in that field of the READ CAPACITY
(16) parameter data, but nothing else in the driver acts on it: the data
it stores begins at LBA 0 and has no physical block structure behind it.

That does not matter for a device that is not zoned, where a write need
not end on a physical block boundary at all. It does matter for a zoned
device: ZBC requires a write to a sequential write required zone to end
on a physical block boundary, and a zone begins at a multiple of the
zone size, so a non-zero lowest aligned LBA puts the beginning of every
zone in the middle of a physical block. A host that writes in units of
the zone write granularity that it was given can then never satisfy the
requirement, and such a zone cannot be written at all.

Refuse the combination rather than emulate a device that cannot be used.

Assisted-by: LLM
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
Tested by loading the module with each combination:

  zbc=managed lowest_aligned=8    refused, -EINVAL
  zbc=aware   lowest_aligned=8    refused, -EINVAL
  zbc=managed lowest_aligned=0    loads
  lowest_aligned=8                loads, as the device is not zoned
---
 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 6941809dfdb7..c664966e95cb 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -8734,6 +8734,11 @@ static int __init scsi_debug_init(void)
 			sdebug_dev_size_mb = DEF_ZBC_DEV_SIZE_MB;
 	}
 
+	if (sdeb_zbc_in_use && sdebug_lowest_aligned) {
+		pr_err("lowest_aligned 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)

base-commit: c3cff7fac01638ab58e85fe7df41a04fa25c5bae
-- 
2.55.0