Re: [PATCH 1/2] btrfs: introduce BTRFS_DEFAULT_RESERVED macro

[Nikolay Borisov <nborisov@suse.com>]

On 13.06.22 г. 10:06 ч., Qu Wenruo wrote:
> Since btrfs-progs v4.1, mkfs.btrfs will reserve the first 1MiB for the
> primary super block (at offset 64KiB) and other legacy bootloaders which
> may want to store their data there.
> 
> Kernel is doing the same behavior around the same time.
> 
> However in kernel we just use SZ_1M to express the reserved space, normally
> with extra comments when using above SZ_1M.
> 
> Here we introduce a new macro, BTRFS_DEFAULT_RESERVED to replace such
> SZ_1M usage.
> 
> This will make later enlarged per-dev reservation easier to implement.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/ctree.h       |  7 +++++++
>   fs/btrfs/extent-tree.c |  6 +++---
>   fs/btrfs/super.c       | 10 +++++-----
>   fs/btrfs/volumes.c     |  7 +------
>   4 files changed, 16 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index f7afdfd0bae7..62028e7d5799 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -229,6 +229,13 @@ struct btrfs_root_backup {
>   #define BTRFS_SUPER_INFO_OFFSET			SZ_64K
>   #define BTRFS_SUPER_INFO_SIZE			4096
>   
> +/*
> + * The default reserved space for each device.
> + * This range covers the primary superblock, and some other legacy programs like
> + * older bootloader may want to store their data there.
> + */
> +#define BTRFS_DEFAULT_RESERVED			(SZ_1M)
> +

The name of this macros is too generic and uninformative. How about 
BTRFS_BOOT_RESERVED or simply BTRFS_RESERVED_SPACE, because 
BTRFS_DEFAULT_RESERVED implies  there is something else, apart from 
"default" and there won't be ...

<snip>