null_blk: Do not allow runt zone with zone capacity smaller then zone…

… size

A zoned device with a smaller last zone together with a zone capacity
smaller than the zone size does make any sense as that does not
correspond to any possible setup for a real device:
1) For ZNS and zoned UFS devices, all zones are always the same size.
2) For SMR HDDs, all zones always have the same capacity.
In other words, if we have a smaller last runt zone, then this zone
capacity should always be equal to the zone size.

Add a check in null_init_zoned_dev() to prevent a configuration to have
both a smaller zone size and a zone capacity smaller than the zone size.

Signed-off-by: Damien Le Moal <[email protected]>
Reviewed-by: Niklas Cassel <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

drivers/block/null_blk/zoned.c

@@ -74,6 +74,17 @@ int null_init_zoned_dev(struct nullb_device *dev,
  return -EINVAL;
  }
 
+ /*
+ * If a smaller zone capacity was requested, do not allow a smaller last
+ * zone at the same time as such zone configuration does not correspond
+ * to any real zoned device.
+ */
+ if (dev->zone_capacity != dev->zone_size &&
+ dev->size & (dev->zone_size - 1)) {
+ pr_err("A smaller last zone is not allowed with zone capacity smaller than zone size.\n");
+ return -EINVAL;
+ }
+
  zone_capacity_sects = mb_to_sects(dev->zone_capacity);
  dev_capacity_sects = mb_to_sects(dev->size);
  dev->zone_size_sects = mb_to_sects(dev->zone_size);