[PATCH v4 05/27] btrfs: disallow space_cache in HMZONED mode

[Naohiro Aota <naohiro.aota@xxxxxxx>]

As updates to the space cache are in-place, the space cache cannot be
located over sequential zones and there is no guarantees that the device
will have enough conventional zones to store this cache. Resolve this
problem by disabling completely the space cache.  This does not introduces
any problems with sequential block groups: all the free space is located
after the allocation pointer and no free space before the pointer. There is
no need to have such cache.

Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
---
 fs/btrfs/hmzoned.c | 18 ++++++++++++++++++
 fs/btrfs/hmzoned.h |  1 +
 fs/btrfs/super.c   | 10 ++++++++--
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/hmzoned.c b/fs/btrfs/hmzoned.c
index 84b7b561840d..8f0b17eba4b3 100644
--- a/fs/btrfs/hmzoned.c
+++ b/fs/btrfs/hmzoned.c
@@ -231,3 +231,21 @@ int btrfs_check_hmzoned_mode(struct btrfs_fs_info *fs_info)
 out:
 	return ret;
 }
+
+int btrfs_check_mountopts_hmzoned(struct btrfs_fs_info *info)
+{
+	if (!btrfs_fs_incompat(info, HMZONED))
+		return 0;
+
+	/*
+	 * SPACE CACHE writing is not CoWed. Disable that to avoid
+	 * write errors in sequential zones.
+	 */
+	if (btrfs_test_opt(info, SPACE_CACHE)) {
+		btrfs_err(info,
+		  "cannot enable disk space caching with HMZONED mode");
+		return -EINVAL;
+	}
+
+	return 0;
+}
diff --git a/fs/btrfs/hmzoned.h b/fs/btrfs/hmzoned.h
index 29cfdcabff2f..83579b2dc0a4 100644
--- a/fs/btrfs/hmzoned.h
+++ b/fs/btrfs/hmzoned.h
@@ -28,6 +28,7 @@ int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
 int btrfs_get_dev_zone_info(struct btrfs_device *device);
 void btrfs_destroy_dev_zone_info(struct btrfs_device *device);
 int btrfs_check_hmzoned_mode(struct btrfs_fs_info *fs_info);
+int btrfs_check_mountopts_hmzoned(struct btrfs_fs_info *info);
 
 static inline bool btrfs_dev_is_sequential(struct btrfs_device *device, u64 pos)
 {
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d7879a5a2536..496d8b74f9a2 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -440,8 +440,12 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 	cache_gen = btrfs_super_cache_generation(info->super_copy);
 	if (btrfs_fs_compat_ro(info, FREE_SPACE_TREE))
 		btrfs_set_opt(info->mount_opt, FREE_SPACE_TREE);
-	else if (cache_gen)
-		btrfs_set_opt(info->mount_opt, SPACE_CACHE);
+	else if (cache_gen) {
+		if (btrfs_fs_incompat(info, HMZONED))
+			WARN_ON(1);
+		else
+			btrfs_set_opt(info->mount_opt, SPACE_CACHE);
+	}
 
 	/*
 	 * Even the options are empty, we still need to do extra check
@@ -877,6 +881,8 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 		ret = -EINVAL;
 
 	}
+	if (!ret)
+		ret = btrfs_check_mountopts_hmzoned(info);
 	if (!ret && btrfs_test_opt(info, SPACE_CACHE))
 		btrfs_info(info, "disk space caching is enabled");
 	if (!ret && btrfs_test_opt(info, FREE_SPACE_TREE))
-- 
2.23.0