Re: [PATCH 3/9] btrfs-progs: allocate blocks from the start of the temp system chunk

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2021/8/21 上午3:11, Josef Bacik wrote:
> During mkfs we skip allocating a block for the super block, however
> because we're using the blocks array iterator to determine the offset of
> our block we're leaving a hole at the beginning of the temporary chunk.
> This isn't a problem per-se, but I'm going to start generating the free
> space tree at make_btrfs() time and having this hole makes the free
> space tree creation slightly more complicated.
>
> Instead keep track of which block we're on so that we start from the
> actual offset of the system chunk.

Can't we just get rid the extra block for superblock?

As the superblock is always located at a fixed location, we don't really
need to put it into the blocks[] array.

Thanks,
Qu
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
>   mkfs/common.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mkfs/common.c b/mkfs/common.c
> index 8902d39e..0e747301 100644
> --- a/mkfs/common.c
> +++ b/mkfs/common.c
> @@ -153,6 +153,7 @@ int make_btrfs(int fd, struct btrfs_mkfs_config *cfg)
>   	u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
>   	u8 *ptr;
>   	int i;
> +	int cnt;
>   	int ret;
>   	int blocks_nr = ARRAY_SIZE(extent_tree_v1_blocks);
>   	int blk;
> @@ -203,11 +204,11 @@ int make_btrfs(int fd, struct btrfs_mkfs_config *cfg)
>   	uuid_generate(chunk_tree_uuid);
>
>   	cfg->blocks[MKFS_SUPER_BLOCK] = BTRFS_SUPER_INFO_OFFSET;
> -	for (i = 0; i < blocks_nr; i++) {
> +	for (cnt = 0, i = 0; i < blocks_nr; i++) {
>   		blk = blocks[i];
>   		if (blk == MKFS_SUPER_BLOCK)
>   			continue;
> -		cfg->blocks[blk] = system_group_offset + cfg->nodesize * i;
> +		cfg->blocks[blk] = system_group_offset + cfg->nodesize * cnt++;
>   		total_used += cfg->nodesize;
>   	}
>
>