[PATCH v2] block: Check partition alignment on zoned block devices

* [PATCH v2] block: Check partition alignment on zoned block devices
@ 2016-12-01  0:22 Damien Le Moal
  2016-12-01  1:40 ` Jens Axboe
  0 siblings, 1 reply; 6+ messages in thread
From: Damien Le Moal @ 2016-12-01  0:22 UTC (permalink / raw)
  To: Jens Axboe; +Cc: linux-block, Shaun Tancheff, Damien Le Moal

Both blkdev_report_zones and blkdev_reset_zones can operate on a partition of
a zoned block device. However, the first and last zones reported for a
partition make sense only if the partition start sector and size are aligned
on the device zone size. The same applies for zone reset. Resetting the first
or the last zone of a partition straddling zones may impact neighboring
partitions. Finally, if a partition start sector is not at the beginning of a
sequential zone, it will be impossible to write to the first sectors of the
partition on a host-managed device.
Avoid all these problems and incoherencies by ignoring partitions that are not
zone aligned.

Note: Even with CONFIG_BLK_DEV_ZONED disabled, bdev_is_zoned() will report the
correct disk zoning type (host-aware, host-managed or none) but
bdev_zone_size() will always return 0 for zoned block devices (i.e. the zone
size is unknown). So test this as a way to ensure that a zoned block device is
being handled as such. As a result, for a host-aware devices, unaligned zone
partitions will be accepted with CONFIG_BLK_DEV_ZONED disabled. That is, the
disk will be treated as a regular block device (as it should). If zoned block
device support is enabled, only aligned partitions will be accepted.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
---
 block/partition-generic.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/block/partition-generic.c b/block/partition-generic.c
index 71d9ed9..3bb9f13 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -430,6 +430,27 @@ static int drop_partitions(struct gendisk *disk, struct block_device *bdev)
 	return 0;
 }
 
+static bool part_zone_aligned(struct gendisk *disk,
+			      struct block_device *bdev,
+			      sector_t from, sector_t size)
+{
+	sector_t zone_size = bdev_zone_size(bdev);
+
+	/* Check partition start alignement */
+	if (from & (zone_size - 1))
+		return false;
+
+	/*
+	 * Check partition end alignement.
+	 * Ignore eventual last smaller zone.
+	 */
+	if ((from + size) < get_capacity(disk) &&
+	    (size & (zone_size - 1)))
+		return false;
+
+	return true;
+}
+
 int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
 {
 	struct parsed_partitions *state = NULL;
@@ -529,6 +550,25 @@ int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
 			}
 		}
 
+		/*
+		 * On a zoned block device, partitions should be aligned on the
+		 * device zone size (i.e. zone boundary crossing not allowed).
+		 * Otherwise, resetting the write pointer of the last zone of
+		 * one partition may impact the following partition. Note that
+		 * bdev_is_zoned() always returns the correct device zoning type
+		 * (host-aware, host-managed or none), even when support for
+		 * zoned block devices is disabled. However, in this last case,
+		 * the zone size will be reported as 0.
+		 */
+		if (bdev_is_zoned(bdev) &&
+		    bdev_zone_size(bdev) &&
+		    !part_zone_aligned(disk, bdev, from, size)) {
+			printk(KERN_WARNING
+			       "%s: p%d start %llu is not zone unaligned\n",
+			       disk->disk_name, p, (unsigned long long) from);
+			continue;
+		}
+
 		part = add_partition(disk, p, from, size,
 				     state->parts[p].flags,
 				     &state->parts[p].info);
-- 
2.7.4

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