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btrfs: simplify tree block checksumming loop

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Thw whole point of csum_tree_block is to iterate over all extent buffer
pages and pass it to checksumming functions. The bytes where checksum is
stored must be skipped, thus map_private_extent_buffer. This complicates
further offset calculations.

As the first page will be always present, checksum the relevant bytes
unconditionally and then do a simple iteration over the remaining pages.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2020-02-27 21:00:47 +01:00
parent 59a0fcdb48
commit e9be5a303d
1 changed files with 8 additions and 24 deletions
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32
fs/btrfs/disk-io.c
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@ -259,38 +259,22 @@ out:
static int csum_tree_block(struct extent_buffer *buf, u8 *result)
{
struct btrfs_fs_info *fs_info = buf->fs_info;
const int num_pages = fs_info->nodesize >> PAGE_SHIFT;
SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
unsigned long len;
unsigned long cur_len;
unsigned long offset = BTRFS_CSUM_SIZE;
char *kaddr;
unsigned long map_start;
unsigned long map_len;
int err;
int i;
shash->tfm = fs_info->csum_shash;
crypto_shash_init(shash);
kaddr = page_address(buf->pages[0]);
crypto_shash_update(shash, kaddr + BTRFS_CSUM_SIZE,
PAGE_SIZE - BTRFS_CSUM_SIZE);
len = buf->len - offset;
while (len > 0) {
/*
* Note: we don't need to check for the err == 1 case here, as
* with the given combination of 'start = BTRFS_CSUM_SIZE (32)'
* and 'min_len = 32' and the currently implemented mapping
* algorithm we cannot cross a page boundary.
*/
err = map_private_extent_buffer(buf, offset, 32,
&kaddr, &map_start, &map_len);
if (WARN_ON(err))
return err;
cur_len = min(len, map_len - (offset - map_start));
crypto_shash_update(shash, kaddr + offset - map_start, cur_len);
len -= cur_len;
offset += cur_len;
for (i = 1; i < num_pages; i++) {
kaddr = page_address(buf->pages[i]);
crypto_shash_update(shash, kaddr, PAGE_SIZE);
}
memset(result, 0, BTRFS_CSUM_SIZE);
crypto_shash_final(shash, result);
return 0;