[v4] block: Check partition alignment on zoned block devices

Commit Message

Damien Le Moal Dec. 1, 2016, 7 a.m. UTC

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 <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>

---
 block/partition-generic.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

Comments

Jens Axboe Dec. 1, 2016, 2:57 p.m. UTC | #1

On 12/01/2016 12:00 AM, Damien Le Moal wrote:
> 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.

Thanks Damien, applied.

Patch

diff --git a/block/partition-generic.c b/block/partition-generic.c
index 71d9ed9..d7beb6b 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -430,6 +430,56 @@  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)
+{
+	unsigned int zone_size = bdev_zone_size(bdev);
+
+	/*
+	 * If this function is called, then the disk is a zoned block device
+	 * (host-aware or host-managed). This can be detected even if the
+	 * zoned block device support is disabled (CONFIG_BLK_DEV_ZONED not
+	 * set). In this case, however, only host-aware devices will be seen
+	 * as a block device is not created for host-managed devices. Without
+	 * zoned block device support, host-aware drives can still be used as
+	 * regular block devices (no zone operation) and their zone size will
+	 * be reported as 0. Allow this case.
+	 */
+	if (!zone_size)
+		return true;
+
+	/*
+	 * Check partition start and size alignement. If the drive has a
+	 * smaller last runt zone, ignore it and allow the partition to
+	 * use it. Check the zone size too: it should be a power of 2 number
+	 * of sectors.
+	 */
+	if (WARN_ON_ONCE(!is_power_of_2(zone_size))) {
+		u32 rem;
+
+		div_u64_rem(from, zone_size, &rem);
+		if (rem)
+			return false;
+		if ((from + size) < get_capacity(disk)) {
+			div_u64_rem(size, zone_size, &rem);
+			if (rem)
+				return false;
+		}
+
+	} else {
+
+		if (from & (zone_size - 1))
+			return false;
+		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 +579,21 @@  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.
+		 */
+		if (bdev_is_zoned(bdev) &&
+		    !part_zone_aligned(disk, bdev, from, size)) {
+			printk(KERN_WARNING
+			       "%s: p%d start %llu+%llu is not zone aligned\n",
+			       disk->disk_name, p, (unsigned long long) from,
+			       (unsigned long long) size);
+			continue;
+		}
+
 		part = add_partition(disk, p, from, size,
 				     state->parts[p].flags,
 				     &state->parts[p].info);