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btrfs: scrub: refactor scrub_find_csum() 

Function scrub_find_csum() is to locate the csum for bytenr @logical
from sctx->csum_list.

However it lacks a lot of comments to explain 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 comments 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>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2020-11-03 21:31:04 +08:00 committed by David Sterba
parent 96e63a45fb
commit 480a8ec83b
1 changed files with 48 additions and 21 deletions
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55
fs/btrfs/scrub.c
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@ -2362,38 +2362,65 @@ static void scrub_block_complete(struct scrub_block *sblock)
}
}
static void drop_csum_range(struct scrub_ctx *sctx, struct btrfs_ordered_sum *sum)
{
sctx->stat.csum_discards += sum->len >> sctx->fs_info->sectorsize_bits;
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)
{
bool found = false;
while (!list_empty(&sctx->csum_list)) {
struct btrfs_ordered_sum *sum = NULL;
unsigned long index;
unsigned long num_sectors;
while (!list_empty(&sctx->csum_list)) {
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;
/*
* 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 with the range,
* and continue search the next range.
*/
if (sum->bytenr + sum->len <= logical) {
drop_csum_range(sctx, sum);
continue;
}
if (!sum)
return 0;
/* Now the csum range covers our bytenr, copy the csum */
found = true;
index = (logical - sum->bytenr) >> sctx->fs_info->sectorsize_bits;
ASSERT(index < UINT_MAX);
num_sectors = sum->len >> sctx->fs_info->sectorsize_bits;
memcpy(csum, sum->sums + index * sctx->fs_info->csum_size,
sctx->fs_info->csum_size);
if (index == num_sectors - 1) {
list_del(&sum->list);
kfree(sum);
/* 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;
}