block: allow partitions on host aware zone devices

Host-aware SMR drives can be used with the commands to explicitly manage
zone state, but they can also be used as normal disks. In the former
case it makes perfect sense to allow partitions on them, in the latter
it does not, just like for host managed devices. Add a check to
add_partition to allow partitions on host aware devices, but give
up any zone management capabilities in that case, which also catches
the previously missed case of adding a partition vs just scanning it.

Because sd can rescan the attribute at runtime it needs to check if
a disk has partitions, for which a new helper is added to genhd.h.

Fixes: 5eac3eb30c9a ("block: Remove partition support for zoned block devices")
Reported-by: Borislav Petkov <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>
Tested-by: Damien Le Moal <[e-mail]>
Reviewed-by: Damien Le Moal <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

block/partition-generic.c

···
 	const char *dname;
 	int err;
 
+	/*
+	 * Partitions are not supported on zoned block devices that are used as
+	 * such.
+	 */
+	switch (disk->queue->limits.zoned) {
+	case BLK_ZONED_HM:
+		pr_warn("%s: partitions not supported on host managed zoned block device\n",
+			disk->disk_name);
+		return ERR_PTR(-ENXIO);
+	case BLK_ZONED_HA:
+		pr_info("%s: disabling host aware zoned block device support due to partitions\n",
+			disk->disk_name);
+		disk->queue->limits.zoned = BLK_ZONED_NONE;
+		break;
+	case BLK_ZONED_NONE:
+		break;
+	}
+
 	err = disk_expand_part_tbl(disk, partno);
 	if (err)
 		return ERR_PTR(err);
···
 
 	part = add_partition(disk, p, from, size, state->parts[p].flags,
 			     &state->parts[p].info);
-	if (IS_ERR(part)) {
+	if (IS_ERR(part) && PTR_ERR(part) != -ENXIO) {
 		printk(KERN_ERR " %s: p%d could not be added: %ld\n",
 		       disk->disk_name, p, -PTR_ERR(part));
 		return true;
···
 	}
 
 	/*
-	 * Partitions are not supported on zoned block devices.
+	 * Partitions are not supported on host managed zoned block devices.
 	 */
-	if (bdev_is_zoned(bdev)) {
-		pr_warn("%s: ignoring partition table on zoned block device\n",
+	if (disk->queue->limits.zoned == BLK_ZONED_HM) {
+		pr_warn("%s: ignoring partition table on host managed zoned block device\n",
 			disk->disk_name);
 		ret = 0;
 		goto out_free_state;

drivers/scsi/sd.c

···
 		q->limits.zoned = BLK_ZONED_HM;
 	} else {
 		sdkp->zoned = (buffer[8] >> 4) & 3;
-		if (sdkp->zoned == 1)
+		if (sdkp->zoned == 1 && !disk_has_partitions(sdkp->disk)) {
 			/* Host-aware */
 			q->limits.zoned = BLK_ZONED_HA;
-		else
+		} else {
 			/*
-			 * Treat drive-managed devices as
-			 * regular block devices.
+			 * Treat drive-managed devices and host-aware devices
+			 * with partitions as regular block devices.
 			 */
 			q->limits.zoned = BLK_ZONED_NONE;
+		}
 	}
 	if (blk_queue_is_zoned(q) && sdkp->first_scan)
 		sd_printk(KERN_NOTICE, sdkp, "Host-%s zoned block device\n",

include/linux/genhd.h

···
 		!(disk->flags & GENHD_FL_NO_PART_SCAN);
 }
 
+static inline bool disk_has_partitions(struct gendisk *disk)
+{
+	bool ret = false;
+
+	rcu_read_lock();
+	if (rcu_dereference(disk->part_tbl)->len > 1)
+		ret = true;
+	rcu_read_unlock();
+
+	return ret;
+}
+
 static inline dev_t disk_devt(struct gendisk *disk)
 {
 	return MKDEV(disk->major, disk->first_minor);