Re: [PATCH 4/8] btrfs: scrub: refactor scrub_find_csum()

Josef Bacik
2020-10-26T14:40:13Z

On 10/26/20 3:11 AM, Qu Wenruo wrote:
> Function scrub_find_csum() is to locate the csum for bytenr @logical
> from sctx->csum_list.
>
> However it lacks a lot of comments to explaining things like how the
> csum_list is organized and why we need to drop csum range which is
> before us.
>
> Refactor the function by:
> - Add more comment explaining the behavior
> - Add comment explaining why we need to drop the csum range
> - Put the csum copy in the main loop
> This is mostly for the incoming patches to make scrub_find_csum() able
> to find multiple checksums.
>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> fs/btrfs/scrub.c | 70 +++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 51 insertions(+), 19 deletions(-)
>
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index 321d6d457942..0d078393f986 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -2386,37 +2386,69 @@ static void scrub_block_complete(struct scrub_block *sblock)
> }
> }
>
> +static void drop_csum_range(struct scrub_ctx *sctx,
> + struct btrfs_ordered_sum *sum)
> +{
> + u32 sectorsize = sctx->fs_info->sectorsize;
> +
> + sctx->stat.csum_discards += sum->len / sectorsize;
> + list_del(&sum->list);
> + kfree(sum);
> +}
> +
> +/*
> + * Find the desired csum for range [@logical, @logical + sectorsize), and
> + * store the csum into @csum.
> + *
> + * The search source is sctx->csum_list, which is a pre-populated list
> + * storing bytenr ordered csum ranges.
> + * We're reponsible to cleanup any range that is before @logical.
> + *
> + * Return 0 if there is no csum for the range.
> + * Return 1 if there is csum for the range and copied to @csum.
> + */
> static int scrub_find_csum(struct scrub_ctx *sctx, u64 logical, u8 *csum)
> {
> - struct btrfs_ordered_sum *sum = NULL;
> - unsigned long index;
> - unsigned long num_sectors;
> + u32 sectorsize = sctx->fs_info->sectorsize;
> + u32 csum_size = sctx->csum_size;
> + bool found = false;
>
> while (!list_empty(&sctx->csum_list)) {
> + struct btrfs_ordered_sum *sum = NULL;
> + unsigned long index;
> + unsigned long num_sectors;
> +
> sum = list_first_entry(&sctx->csum_list,
> struct btrfs_ordered_sum, list);
> + /* The current csum range is beyond our range, no csum found */
> if (sum->bytenr > logical)
> - return 0;
> - if (sum->bytenr + sum->len > logical)
> break;
>
> - ++sctx->stat.csum_discards;
> - list_del(&sum->list);
> - kfree(sum);
> - sum = NULL;
> - }
> - if (!sum)
> - return 0;
> + /*
> + * The current sum is before our bytenr, since scrub is
> + * always done in bytenr order, the csum will never be used
> + * anymore, clean it up so that later calls won't bother the
> + * range, and continue search the next range.
> + */
> + if (sum->bytenr + sum->len <= logical) {
> + drop_csum_range(sctx, sum);
> + continue;
> + }
>
> - index = div_u64(logical - sum->bytenr, sctx->fs_info->sectorsize);
> - ASSERT(index < UINT_MAX);
> + /* Now the csum range covers our bytenr, copy the csum */
> + found = true;
> + index = div_u64(logical - sum->bytenr, sectorsize);
> + num_sectors = sum->len / sectorsize;
>
> - num_sectors = sum->len / sctx->fs_info->sectorsize;
> - memcpy(csum, sum->sums + index * sctx->csum_size, sctx->csum_size);
> - if (index == num_sectors - 1) {
> - list_del(&sum->list);
> - kfree(sum);
> + memcpy(csum, sum->sums + index * csum_size, csum_size);
> +
> + /* Cleanup the range if we're at the end of the csum range */
> + if (index == num_sectors - 1)
> + drop_csum_range(sctx, sum);
> + break;
> }
> + if (!found)
> + return 0;
> return 1;
> }

If it's just a bool we're returning, change this to

static bool scrub_find_csum()

and do

return found.

Thanks,

Josef