dm: fix native zone append devices on top of emulated ones

If a DM device that can pass down zone append commands is stacked on top
of a device that emulates zone append commands, it will allocate zone
append emulation resources, even though it doesn't use them. This is
because the underlying device will have max_hw_zone_append_sectors set
to 0 to request zone append emulation. When the DM device is stacked on
top of it, it will inherit that max_hw_zone_append_sectors limit,
despite being able to pass down zone append bios. Solve this by making
sure max_hw_zone_append_sectors is non-zero for DM devices that do not
need zone append emulation.

Reviewed-by: Damien Le Moal <[email protected]>
Tested-by: Damien Le Moal <[email protected]>
Signed-off-by: Benjamin Marzinski <[email protected]>
Signed-off-by: Mikulas Patocka <[email protected]>

Author: bmarzins

drivers/md/dm-zone.c

@@ -347,11 +347,15 @@ int dm_set_zones_restrictions(struct dm_table *t, struct request_queue *q,
 
 	/*
 	 * Check if zone append is natively supported, and if not, set the
-	 * mapped device queue as needing zone append emulation.
+	 * mapped device queue as needing zone append emulation. If zone
+	 * append is natively supported, make sure that
+	 * max_hw_zone_append_sectors is not set to 0.
 	 */
 	WARN_ON_ONCE(queue_is_mq(q));
 	if (!dm_table_supports_zone_append(t))
 		lim->max_hw_zone_append_sectors = 0;
+	else if (lim->max_hw_zone_append_sectors == 0)
+		lim->max_hw_zone_append_sectors = lim->max_zone_append_sectors;
 
 	/*
 	 * Determine the max open and max active zone limits for the mapped