[PATCH 01/15] btrfs: stop enabling the v1 space cache from the on-disk state

[Tal Zussman]

Since commit 545e560a5b0f ("btrfs: disable v1 space cache") the mount
options can no longer request the v1 space cache, but a filesystem with
an active v1 cache and no free space tree still enables it from
cache_generation, and remount does the same. Drop both, so SPACE_CACHE
can never be set.

btrfs_start_pre_rw_mount() then sees the on-disk cache as active but
unwanted and cleans it up, as -o nospace_cache does today. That covers
the read-only to read-write remount as well, so drop the toggle in
btrfs_remount_cleanup(), which would otherwise start a transaction on
remounts of a read-only filesystem with an old cache.

The cleanup is now unconditional, and the first read-write mount fails
if it fails, as it did with -o nospace_cache. This also lets an old
filesystem mount without options when the page size is larger than the
sector size, which btrfs_check_features() rejected once SPACE_CACHE was
set from the superblock.

Assisted-by: Claude:claude-fable-5-1
Signed-off-by: Tal Zussman <tz2294@xxxxxxxxxxxx>
---
 fs/btrfs/super.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 464129b1b0d4..77443ded6db3 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -759,12 +759,12 @@ void btrfs_set_free_space_cache_settings(struct btrfs_fs_info *fs_info)
 
 	/*
 	 * At this point we don't have explicit options set by the user, set
-	 * them ourselves based on the state of the file system.
+	 * them ourselves based on the state of the file system. An existing
+	 * v1 space cache is no longer used and gets cleaned up once the
+	 * filesystem is mounted read-write.
 	 */
 	if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE))
 		btrfs_set_opt(fs_info->mount_opt, FREE_SPACE_TREE);
-	else if (btrfs_free_space_cache_v1_active(fs_info))
-		btrfs_set_opt(fs_info->mount_opt, SPACE_CACHE);
 }
 
 static void set_device_specific_options(struct btrfs_fs_info *fs_info)
@@ -1264,8 +1264,6 @@ static inline void btrfs_remount_begin(struct btrfs_fs_info *fs_info,
 static inline void btrfs_remount_cleanup(struct btrfs_fs_info *fs_info,
 					 unsigned long long old_opts)
 {
-	const bool cache_opt = btrfs_test_opt(fs_info, SPACE_CACHE);
-
 	/*
 	 * We need to cleanup all defraggable inodes if the autodefragment is
 	 * close or the filesystem is read only.
@@ -1282,10 +1280,6 @@ static inline void btrfs_remount_cleanup(struct btrfs_fs_info *fs_info,
 	else if (btrfs_raw_test_opt(old_opts, DISCARD_ASYNC) &&
 		 !btrfs_test_opt(fs_info, DISCARD_ASYNC))
 		btrfs_discard_cleanup(fs_info);
-
-	/* If we toggled space cache */
-	if (cache_opt != btrfs_free_space_cache_v1_active(fs_info))
-		btrfs_set_free_space_cache_v1_active(fs_info, cache_opt);
 }
 
 static int btrfs_remount_rw(struct btrfs_fs_info *fs_info)
@@ -1535,10 +1529,6 @@ static int btrfs_reconfigure(struct fs_context *fc)
 			btrfs_set_opt(fs_info->mount_opt, FREE_SPACE_TREE);
 			btrfs_clear_opt(fs_info->mount_opt, SPACE_CACHE);
 		}
-		if (btrfs_free_space_cache_v1_active(fs_info)) {
-			btrfs_clear_opt(fs_info->mount_opt, FREE_SPACE_TREE);
-			btrfs_set_opt(fs_info->mount_opt, SPACE_CACHE);
-		}
 	}
 
 	ret = 0;

-- 
2.39.5