btrfs: cleanup the main loop in btrfs_lookup_bio_sums

Introduce a bio_offset variable for the current offset into the bio
instead of recalculating it over and over.   Remove the now only used
once search_len and sector_offset variables, and reduce the scope for
count and cur_disk_bytenr.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 9df9b91..1ce306c 100644 (file)
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -350,10 +350,9 @@ blk_status_t btrfs_lookup_bio_sums(struct btrfs_bio *bbio)
        const u32 csum_size = fs_info->csum_size;
        u32 orig_len = bio->bi_iter.bi_size;
        u64 orig_disk_bytenr = bio->bi_iter.bi_sector << SECTOR_SHIFT;
-       u64 cur_disk_bytenr;
        const unsigned int nblocks = orig_len >> fs_info->sectorsize_bits;
-       int count = 0;
        blk_status_t ret = BLK_STS_OK;
+       u32 bio_offset = 0;
 
        if ((inode->flags & BTRFS_INODE_NODATASUM) ||
            test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state))
@@ -404,28 +403,14 @@ blk_status_t btrfs_lookup_bio_sums(struct btrfs_bio *bbio)
                path->skip_locking = 1;
        }
 
-       for (cur_disk_bytenr = orig_disk_bytenr;
-            cur_disk_bytenr < orig_disk_bytenr + orig_len;
-            cur_disk_bytenr += (count * sectorsize)) {
-               u64 search_len = orig_disk_bytenr + orig_len - cur_disk_bytenr;
-               unsigned int sector_offset;
-               u8 *csum_dst;
-
-               /*
-                * Although both cur_disk_bytenr and orig_disk_bytenr is u64,
-                * we're calculating the offset to the bio start.
-                *
-                * Bio size is limited to UINT_MAX, thus unsigned int is large
-                * enough to contain the raw result, not to mention the right
-                * shifted result.
-                */
-               ASSERT(cur_disk_bytenr - orig_disk_bytenr < UINT_MAX);
-               sector_offset = (cur_disk_bytenr - orig_disk_bytenr) >>
-                               fs_info->sectorsize_bits;
-               csum_dst = bbio->csum + sector_offset * csum_size;
+       while (bio_offset < orig_len) {
+               int count;
+               u64 cur_disk_bytenr = orig_disk_bytenr + bio_offset;
+               u8 *csum_dst = bbio->csum +
+                       (bio_offset >> fs_info->sectorsize_bits) * csum_size;
 
                count = search_csum_tree(fs_info, path, cur_disk_bytenr,
-                                        search_len, csum_dst);
+                                        orig_len - bio_offset, csum_dst);
                if (count < 0) {
                        ret = errno_to_blk_status(count);
                        if (bbio->csum != bbio->csum_inline)
@@ -450,8 +435,7 @@ blk_status_t btrfs_lookup_bio_sums(struct btrfs_bio *bbio)
 
                        if (inode->root->root_key.objectid ==
                            BTRFS_DATA_RELOC_TREE_OBJECTID) {
-                               u64 file_offset = bbio->file_offset +
-                                       cur_disk_bytenr - orig_disk_bytenr;
+                               u64 file_offset = bbio->file_offset + bio_offset;
 
                                set_extent_bits(&inode->io_tree, file_offset,
                                                file_offset + sectorsize - 1,
@@ -462,6 +446,7 @@ blk_status_t btrfs_lookup_bio_sums(struct btrfs_bio *bbio)
                                cur_disk_bytenr, cur_disk_bytenr + sectorsize);
                        }
                }
+               bio_offset += count * sectorsize;
        }
 
        btrfs_free_path(path);