btrfs: simplify tree block checksumming loop

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>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 483b540..6f63cc4 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -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;