Re: [PATCH v4 01/13] btrfs: scrub: use dedicated super block verification function to scrub one super block

[Christoph Hellwig <hch@infradead.org>]

On Sun, Mar 26, 2023 at 07:06:30PM +0800, Qu Wenruo wrote:
> There is really no need to go through the super complex scrub_sectors()
> to just handle super blocks.
> 
> This patch will introduce a dedicated function (less than 50 lines) to
> handle super block scrubing.
> 
> This new function will introduce a behavior change, instead of using the
> complex but concurrent scrub_bio system, here we just go
> submit-and-wait.
> 
> There is really not much sense to care the performance of super block
> scrubbing. It only has 3 super blocks at most, and they are all scattered
> around the devices already.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/scrub.c | 54 +++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 46 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index 3cdf73277e7e..e765eb8b8bcf 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -4243,18 +4243,59 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
>  	return ret;
>  }
>  
> +static int scrub_one_super(struct scrub_ctx *sctx, struct btrfs_device *dev,
> +			   struct page *page, u64 physical, u64 generation)
> +{
> +	struct btrfs_fs_info *fs_info = sctx->fs_info;
> +	struct bio_vec bvec;
> +	struct bio bio;
> +	struct btrfs_super_block *sb = page_address(page);
> +	int ret;
> +
> +	bio_init(&bio, dev->bdev, &bvec, 1, REQ_OP_READ);
> +	bio.bi_iter.bi_sector = physical >> SECTOR_SHIFT;
> +	bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE, 0);

bio_add_page wants its return value checked.  Now here we obviously
don't need that, but please just use __bio_add_page which has the
proper assert for that.