[v15,04/42] btrfs: zoned: use regular super block location on zone emulation

Commit Message

Naohiro Aota Feb. 4, 2021, 10:21 a.m. UTC

A zoned btrfs filesystem currently has a superblock at the beginning of
the superblock logging zones if the zones are conventional. This
difference in superblock position causes a chicken-and-egg problem for
filesystems with emulated zones. Since the device is a regular (non-zoned)
device, we cannot know if the filesystem is regular or zoned while reading
the superblock. But, to load the superblock, we need to see if it is
emulated zoned or not.

Place the superblocks at the same location as they are on regular btrfs on
regular devices to solve the problem. It is possible because it's ensured
that all the superblock locations are at an (emulated) conventional zone on
regular devices.

Reviewed-by: Anand Jain <[e-mail]>
Reviewed-by: Josef Bacik <[e-mail]>
Signed-off-by: Naohiro Aota <[e-mail]>
---
 fs/btrfs/zoned.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Patch

diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index 0b1b1f38a196..8b3868088c5e 100644
--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -552,7 +552,13 @@  int btrfs_sb_log_location(struct btrfs_device *device, int mirror, int rw,
 	struct btrfs_zoned_device_info *zinfo = device->zone_info;
 	u32 zone_num;
 
-	if (!zinfo) {
+	/*
+	 * For a zoned filesystem on a non-zoned block device, use the same
+	 * super block locations as regular filesystem. Doing so, the super
+	 * block can always be retrieved and the zoned flag of the volume
+	 * detected from the super block information.
+	 */
+	if (!bdev_is_zoned(device->bdev)) {
 		*bytenr_ret = btrfs_sb_offset(mirror);
 		return 0;
 	}