btrfs: simplify eb checksum verification in btrfs_validate_metadata_buffer

The verification copies the calculated checksum bytes to a temporary
buffer but this is not necessary. We can map the eb header on the first
page and use the checksum bytes directly.

This saves at least one function call and boundary checks so it could
lead to a minor performance improvement.

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 b28b314ff7a912a53cfcb2851fcedc4cfd6bec88..34bcd986f738d80e0a32fb9589159dc568297b85 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -584,6 +584,7 @@ static int validate_extent_buffer(struct extent_buffer *eb)
        const u32 csum_size = fs_info->csum_size;
        u8 found_level;
        u8 result[BTRFS_CSUM_SIZE];
+       const u8 *header_csum;
        int ret = 0;
 
        found_start = btrfs_header_bytenr(eb);
@@ -608,15 +609,14 @@ static int validate_extent_buffer(struct extent_buffer *eb)
        }
 
        csum_tree_block(eb, result);
+       header_csum = page_address(eb->pages[0]) +
+               get_eb_offset_in_page(eb, offsetof(struct btrfs_header, csum));
 
-       if (memcmp_extent_buffer(eb, result, 0, csum_size)) {
-               u8 val[BTRFS_CSUM_SIZE] = { 0 };
-
-               read_extent_buffer(eb, &val, 0, csum_size);
+       if (memcmp(result, header_csum, csum_size) != 0) {
                btrfs_warn_rl(fs_info,
        "checksum verify failed on %llu wanted " CSUM_FMT " found " CSUM_FMT " level %d",
                              eb->start,
-                             CSUM_FMT_VALUE(csum_size, val),
+                             CSUM_FMT_VALUE(csum_size, header_csum),
                              CSUM_FMT_VALUE(csum_size, result),
                              btrfs_header_level(eb));
                ret = -EUCLEAN;