null_blk: discard zones on reset

When memory backing is enabled, use null_handle_discard() to free the
backing memory used by a zone when the zone is being reset.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk.h

@@ -116,6 +116,8 @@ struct nullb {
 	char disk_name[DISK_NAME_LEN];
 };
 
+blk_status_t null_handle_discard(struct nullb_device *dev, sector_t sector,
+				 sector_t nr_sectors);
 blk_status_t null_process_cmd(struct nullb_cmd *cmd,
 			      enum req_opf op, sector_t sector,
 			      unsigned int nr_sectors);

drivers/block/null_blk_main.c

@@ -1076,8 +1076,8 @@ static void nullb_fill_pattern(struct nullb *nullb, struct page *page,
 	kunmap_atomic(dst);
 }
 
-static blk_status_t null_handle_discard(struct nullb_device *dev,
-					sector_t sector, sector_t nr_sectors)
+blk_status_t null_handle_discard(struct nullb_device *dev,
+				 sector_t sector, sector_t nr_sectors)
 {
 	struct nullb *nullb = dev->nullb;
 	size_t n = nr_sectors << SECTOR_SHIFT;

drivers/block/null_blk_zoned.c

@@ -588,6 +588,9 @@ static blk_status_t null_reset_zone(struct nullb_device *dev,
 
 	null_unlock_zone_res(dev);
 
+	if (dev->memory_backed)
+		return null_handle_discard(dev, zone->start, zone->len);
+
 	return BLK_STS_OK;
 }