Re: [PATCH 3/3] btrfs-progs: introduce btrfs_rebuild_uuid_tree() for mkfs and btrfs-convert

[David Sterba <dsterba@suse.cz>]

On Fri, Jul 26, 2024 at 07:29:55PM +0930, Qu Wenruo wrote:
> Currently mkfs uses its own create_uuid_tree(), but that function is
> only handling FS_TREE.
> 
> This means for btrfs-convert, we do not generate the uuid tree, nor
> add the UUID of the image subvolume.
> 
> This can be a problem if we're going to support multiple subvolumes
> during mkfs time.
> 
> To address this inconvenience, this patch introduces a new helper,
> btrfs_rebuild_uuid_tree(), which will:
> 
> - Create a new uuid tree if there is not one
> 
> - Empty the existing uuid tree
> 
> - Iterate through all subvolumes
>   * If the subvolume has no valid UUID, regenerate one
>   * Add the uuid entry for the subvolume UUID
>   * If the subvolume has received UUID, also add it to UUID tree
> 
> By this, this new helper can handle all the uuid tree generation needs for:
> 
> - Current mkfs
>   Only one uuid entry for FS_TREE
> 
> - Current btrfs-convert
>   Only FS_TREE and the image subvolume
> 
> - Future multi-subvolume mkfs
>   As we do the scan for all subvolumes.
> 
> - Future "btrfs rescue rebuild-uuid-tree"
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  common/root-tree-utils.c | 265 +++++++++++++++++++++++++++++++++++++++
>  common/root-tree-utils.h |   1 +
>  convert/main.c           |   5 +
>  mkfs/main.c              |  37 +-----
>  4 files changed, 274 insertions(+), 34 deletions(-)
> 
> diff --git a/common/root-tree-utils.c b/common/root-tree-utils.c
> index 6a57c51a8a74..13f89dbd5293 100644
> --- a/common/root-tree-utils.c
> +++ b/common/root-tree-utils.c
> @@ -15,9 +15,11 @@
>   */
>  
>  #include <time.h>
> +#include <uuid/uuid.h>
>  #include "common/root-tree-utils.h"
>  #include "common/messages.h"
>  #include "kernel-shared/disk-io.h"
> +#include "kernel-shared/uuid-tree.h"
>  
>  int btrfs_make_root_dir(struct btrfs_trans_handle *trans,
>  			struct btrfs_root *root, u64 objectid)
> @@ -212,3 +214,266 @@ abort:
>  	btrfs_abort_transaction(trans, ret);
>  	return ret;
>  }
> +
> +static int empty_tree(struct btrfs_root *root)

Please rename this, it's confusing as empty can be a noun and verb so
it's not clear if it's a meant as a predicate or action.