On 2020/2/28 上午4:00, David Sterba wrote:
> 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.
The new operation looks much better.
Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
Thanks,
Qu
>
> Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> ---
> fs/btrfs/disk-io.c | 32 ++++++++------------------------
> 1 file changed, 8 insertions(+), 24 deletions(-)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 3952e4a2f3d7..5f74eb69f2fe 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -259,38 +259,22 @@ struct extent_map *btree_get_extent(struct btrfs_inode *inode,
> 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;
>
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