btrfs: zoned: finish superblock zone once no space left for new SB

If there is no more space left for a new superblock in a superblock zone,
then it is better to ZONE_FINISH the zone and frees up the active zone
count.

Since btrfs_advance_sb_log() can now issue REQ_OP_ZONE_FINISH, we also need
to convert it to return int for the error case.
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -3887,7 +3887,9 @@ static int write_dev_supers(struct btrfs_device *device,
 			bio->bi_opf |= REQ_FUA;
 
 		btrfsic_submit_bio(bio);
-		btrfs_advance_sb_log(device, i);
+
+		if (btrfs_advance_sb_log(device, i))
+			errors++;
 	}
 	return errors < i ? 0 : -1;
 }

fs/btrfs/zoned.c

@@ -789,36 +789,56 @@ static inline bool is_sb_log_zone(struct btrfs_zoned_device_info *zinfo,
 	return true;
 }
 
-void btrfs_advance_sb_log(struct btrfs_device *device, int mirror)
+int btrfs_advance_sb_log(struct btrfs_device *device, int mirror)
 {
 	struct btrfs_zoned_device_info *zinfo = device->zone_info;
 	struct blk_zone *zone;
+	int i;
 
 	if (!is_sb_log_zone(zinfo, mirror))
-		return;
+		return 0;
 
 	zone = &zinfo->sb_zones[BTRFS_NR_SB_LOG_ZONES * mirror];
-	if (zone->cond != BLK_ZONE_COND_FULL) {
+	for (i = 0; i < BTRFS_NR_SB_LOG_ZONES; i++) {
+		/* Advance the next zone */
+		if (zone->cond == BLK_ZONE_COND_FULL) {
+			zone++;
+			continue;
+		}
+
 		if (zone->cond == BLK_ZONE_COND_EMPTY)
 			zone->cond = BLK_ZONE_COND_IMP_OPEN;
 
-		zone->wp += (BTRFS_SUPER_INFO_SIZE >> SECTOR_SHIFT);
+		zone->wp += SUPER_INFO_SECTORS;
 
-		if (zone->wp == zone->start + zone->len)
-			zone->cond = BLK_ZONE_COND_FULL;
+		if (sb_zone_is_full(zone)) {
+			/*
+			 * No room left to write new superblock. Since
+			 * superblock is written with REQ_SYNC, it is safe to
+			 * finish the zone now.
+			 *
+			 * If the write pointer is exactly at the capacity,
+			 * explicit ZONE_FINISH is not necessary.
+			 */
+			if (zone->wp != zone->start + zone->capacity) {
+				int ret;
 
-		return;
+				ret = blkdev_zone_mgmt(device->bdev,
+						REQ_OP_ZONE_FINISH, zone->start,
+						zone->len, GFP_NOFS);
+				if (ret)
+					return ret;
 			}
 
-	zone++;
-	ASSERT(zone->cond != BLK_ZONE_COND_FULL);
-	if (zone->cond == BLK_ZONE_COND_EMPTY)
-		zone->cond = BLK_ZONE_COND_IMP_OPEN;
-
-	zone->wp += (BTRFS_SUPER_INFO_SIZE >> SECTOR_SHIFT);
-
-	if (zone->wp == zone->start + zone->len)
+			zone->wp = zone->start + zone->len;
 			zone->cond = BLK_ZONE_COND_FULL;
+		}
+		return 0;
+	}
+
+	/* All the zones are FULL. Should not reach here. */
+	ASSERT(0);
+	return -EIO;
 }
 
 int btrfs_reset_sb_log_zones(struct block_device *bdev, int mirror)

fs/btrfs/zoned.h

@@ -40,7 +40,7 @@ int btrfs_sb_log_location_bdev(struct block_device *bdev, int mirror, int rw,
 			       u64 *bytenr_ret);
 int btrfs_sb_log_location(struct btrfs_device *device, int mirror, int rw,
 			  u64 *bytenr_ret);
-void btrfs_advance_sb_log(struct btrfs_device *device, int mirror);
+int btrfs_advance_sb_log(struct btrfs_device *device, int mirror);
 int btrfs_reset_sb_log_zones(struct block_device *bdev, int mirror);
 u64 btrfs_find_allocatable_zones(struct btrfs_device *device, u64 hole_start,
 				 u64 hole_end, u64 num_bytes);
@@ -113,8 +113,10 @@ static inline int btrfs_sb_log_location(struct btrfs_device *device, int mirror,
 	return 0;
 }
 
-static inline void btrfs_advance_sb_log(struct btrfs_device *device, int mirror)
-{ }
+static inline int btrfs_advance_sb_log(struct btrfs_device *device, int mirror)
+{
+	return 0;
+}
 
 static inline int btrfs_reset_sb_log_zones(struct block_device *bdev, int mirror)
 {