[PATCH v2 2/3] btrfs: zoned: move superblock logging zone location

[Naohiro Aota <naohiro.aota@wdc.com>]

This commit moves the location of superblock logging zones basing on the
fixed address instead of the fixed zone number.

By locating the superblock zones using fixed addresses, we can scan a
dumped file system image without the zone information. And, no drawbacks
exist.

The following zones are reserved as the circular buffer on zoned btrfs.
  - The primary superblock: zone at LBA 0 and the next zone
  - The first copy: zone at LBA 16G and the next zone
  - The second copy: zone at LBA 256G and the next zone

If the location of the zones are outside of disk, we don't record the
superblock copy.

The addresses are much larger than the usual superblock copies locations.
The copies' locations are decided to support possible future larger zone
size, not to overlap the log zones. We support zone size up to 8GB.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
---
 fs/btrfs/zoned.c | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index 1324bb6c3946..b8f50dc9fbb0 100644
--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -24,6 +24,15 @@
 /* Number of superblock log zones */
 #define BTRFS_NR_SB_LOG_ZONES 2
 
+/* Location of superblock log zones */
+#define BTRFS_FIRST_SB_LOG_ZONE SZ_16G
+#define BTRFS_SECOND_SB_LOG_ZONE (256ULL * SZ_1G)
+#define BTRFS_FIRST_SB_LOG_ZONE_SHIFT const_ilog2(BTRFS_FIRST_SB_LOG_ZONE)
+#define BTRFS_SECOND_SB_LOG_ZONE_SHIFT const_ilog2(BTRFS_SECOND_SB_LOG_ZONE)
+
+/* Max size of supported zone size */
+#define BTRFS_MAX_ZONE_SIZE SZ_8G
+
 static int copy_zone_info_cb(struct blk_zone *zone, unsigned int idx, void *data)
 {
 	struct blk_zone *zones = data;
@@ -112,10 +121,9 @@ static int sb_write_pointer(struct block_device *bdev, struct blk_zone *zones,
 
 /*
  * The following zones are reserved as the circular buffer on ZONED btrfs.
- *  - The primary superblock: zones 0 and 1
- *  - The first copy: zones 16 and 17
- *  - The second copy: zones 1024 or zone at 256GB which is minimum, and
- *                     the following one
+ *  - The primary superblock: zone at LBA 0 and the next zone
+ *  - The first copy: zone at LBA 16G and the next zone
+ *  - The second copy: zone at LBA 256G and the next zone
  */
 static inline u32 sb_zone_number(int shift, int mirror)
 {
@@ -123,8 +131,8 @@ static inline u32 sb_zone_number(int shift, int mirror)
 
 	switch (mirror) {
 	case 0: return 0;
-	case 1: return 16;
-	case 2: return min_t(u64, btrfs_sb_offset(mirror) >> shift, 1024);
+	case 1: return 1 << (BTRFS_FIRST_SB_LOG_ZONE_SHIFT - shift);
+	case 2: return 1 << (BTRFS_SECOND_SB_LOG_ZONE_SHIFT - shift);
 	}
 
 	return 0;
@@ -300,10 +308,25 @@ int btrfs_get_dev_zone_info(struct btrfs_device *device)
 		zone_sectors = bdev_zone_sectors(bdev);
 	}
 
-	nr_sectors = bdev_nr_sectors(bdev);
 	/* Check if it's power of 2 (see is_power_of_2) */
 	ASSERT(zone_sectors != 0 && (zone_sectors & (zone_sectors - 1)) == 0);
 	zone_info->zone_size = zone_sectors << SECTOR_SHIFT;
+
+	/*
+	 * We must reject devices with a zone size larger than 8GB to avoid
+	 * overlap between the super block primary and first copy fixed log
+	 * locations.
+	 */
+	if (zone_info->zone_size > BTRFS_MAX_ZONE_SIZE) {
+		btrfs_err_in_rcu(fs_info,
+				 "zoned: %s: zone size %llu is too large",
+				 rcu_str_deref(device->name),
+				 zone_info->zone_size);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	nr_sectors = bdev_nr_sectors(bdev);
 	zone_info->zone_size_shift = ilog2(zone_info->zone_size);
 	zone_info->max_zone_append_size =
 		(u64)queue_max_zone_append_sectors(queue) << SECTOR_SHIFT;
-- 
2.30.1