block: flag zoned disks with GENHD_FL_NO_PART

Zoned block devices do not support partitions. However, the partition
table is nevertheless still inspected, and any partition found ignored
with a warning in add_partition(). While this is generally not a problem,
and in fact beneficial to the user as it indicates an invalid use of a
zoned block device, scanning for a partition table on the device may
result in issuing read operations to offline zones (e.g. after a disk head
is depopulated for disks that support head management operations).

Since partitions are ignored anyway, completely disable partition scanning
for zoned gendisks by setting the flag GENHD_FL_NO_PART in __add_disk().
The existing check in add_partition() is left as-is to ensure that we
still get a warning if for whatever reason, despite GENHD_FL_NO_PART, we
still endup trying to add partitions.

Flagging zoned disks with GENHD_FL_NO_PART also has the benefit to expose
through sysfs the ext_range attribute with the value of 1 instead of the
default DISK_MAX_PARTS, thus correctly advertizing the fact that zoned
disks do not support partitions.

Fixes: 5eac3eb30c ("block: Remove partition support for zoned block devices")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://patch.msgid.link/20260831025050.667758-1-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -447,6 +447,13 @@ static int __add_disk(struct device *parent, struct gendisk *disk,
 		bdev_set_flag(disk->part0, BD_HAS_SUBMIT_BIO);
 	}
 
+	/*
+	 * We do not support partitions with zoned block devices, so do not try
+	 * to scan the partitions table.
+	 */
+	if (blk_queue_is_zoned(disk->queue))
+		disk->flags |= GENHD_FL_NO_PART;
+
 	/*
 	 * If the driver provides an explicit major number it also must provide
 	 * the number of minors numbers supported, and those will be used to