[PATCH] block: allow partitions on host aware zone devices

[PATCH] block: allow partitions on host aware zone devices

[Christoph Hellwig]

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 <bp@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
---
 block/partition-generic.c | 26 ++++++++++++++++++++++----
 drivers/scsi/sd.c         |  9 +++++----
 include/linux/genhd.h     | 12 ++++++++++++
 3 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/block/partition-generic.c b/block/partition-generic.c
index 1d20c9cf213f..564fae77711d 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -321,6 +321,24 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
 	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);
@@ -501,7 +519,7 @@ static bool blk_add_partition(struct gendisk *disk, struct block_device *bdev,
 
 	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;
@@ -540,10 +558,10 @@ int blk_add_partitions(struct gendisk *disk, struct block_device *bdev)
 	}
 
 	/*
-	 * 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;
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 65ce10c7989c..902b649fc8ef 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2958,15 +2958,16 @@ static void sd_read_block_characteristics(struct scsi_disk *sdkp)
 		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",
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 8bb63027e4d6..ea4c133b4139 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -245,6 +245,18 @@ static inline bool disk_part_scan_enabled(struct gendisk *disk)
 		!(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);
-- 
2.24.1

Re: [PATCH] block: allow partitions on host aware zone devices

[Jens Axboe]

On 1/26/20 6:05 AM, Christoph Hellwig wrote:
> 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.

Applied, thanks.

-- 
Jens Axboe