[PATCH 7/8] btrfs: scrub: support subpage tree block scrub

[Qu Wenruo <wqu@suse.com>]

To support subpage tree block scrub, scrub_checksum_tree_block() only
needs to learn 2 new tricks:
- Follow scrub_page::page_len
  Now scrub_page only represents one sector, we need to follow it
  properly.

- Run checksum on all sectors
  Since scrub_page only represents one sector, we need to run hash on
  all sectors, no longer just (nodesize >> PAGE_SIZE).

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/scrub.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 10836aec389f..13355cc2b1ae 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1841,15 +1841,21 @@ static int scrub_checksum_tree_block(struct scrub_block *sblock)
 	struct scrub_ctx *sctx = sblock->sctx;
 	struct btrfs_header *h;
 	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	u32 sectorsize = sctx->fs_info->sectorsize;
+	u32 nodesize = sctx->fs_info->nodesize;
 	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
 	u8 calculated_csum[BTRFS_CSUM_SIZE];
 	u8 on_disk_csum[BTRFS_CSUM_SIZE];
-	const int num_pages = sctx->fs_info->nodesize >> PAGE_SHIFT;
+	const int num_sectors = nodesize / sectorsize;
 	int i;
 	struct scrub_page *spage;
 	char *kaddr;
 
 	BUG_ON(sblock->page_count < 1);
+
+	/* Each pagev[] is in fact just one sector, not a full page */
+	ASSERT(sblock->page_count == num_sectors);
+
 	spage = sblock->pagev[0];
 	kaddr = page_address(spage->page);
 	h = (struct btrfs_header *)kaddr;
@@ -1878,11 +1884,11 @@ static int scrub_checksum_tree_block(struct scrub_block *sblock)
 	shash->tfm = fs_info->csum_shash;
 	crypto_shash_init(shash);
 	crypto_shash_update(shash, kaddr + BTRFS_CSUM_SIZE,
-			    PAGE_SIZE - BTRFS_CSUM_SIZE);
+			    spage->page_len - BTRFS_CSUM_SIZE);
 
-	for (i = 1; i < num_pages; i++) {
+	for (i = 1; i < num_sectors; i++) {
 		kaddr = page_address(sblock->pagev[i]->page);
-		crypto_shash_update(shash, kaddr, PAGE_SIZE);
+		crypto_shash_update(shash, kaddr, sblock->pagev[i]->page_len);
 	}
 
 	crypto_shash_final(shash, calculated_csum);
-- 
2.29.0