btrfs: introduce a data checksum checking helper

Although we have several data csum verification code, we never have a
function really just to verify checksum for one sector.

Function check_data_csum() do extra work for error reporting, thus it
requires a lot of extra things like file offset, bio_offset etc.

Function btrfs_verify_data_csum() is even worse, it will utilize page
checked flag, which means it can not be utilized for direct IO pages.

Here we introduce a new helper, btrfs_check_sector_csum(), which really
only accept a sector in page, and expected checksum pointer.

We use this function to implement check_data_csum(), and export it for
incoming patch.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
[hch: keep passing the csum array as an arguments, as the callers want
      to print it, rename per request]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -147,12 +147,10 @@ static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio,
 				 u64 disk_start)
 {
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
-	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
 	const u32 csum_size = fs_info->csum_size;
 	const u32 sectorsize = fs_info->sectorsize;
 	struct page *page;
 	unsigned int i;
-	char *kaddr;
 	u8 csum[BTRFS_CSUM_SIZE];
 	struct compressed_bio *cb = bio->bi_private;
 	u8 *cb_sum = cb->sums;
@@ -161,8 +159,6 @@ static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio,
 	    test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state))
 		return 0;
 
-	shash->tfm = fs_info->csum_shash;
-
 	for (i = 0; i < cb->nr_pages; i++) {
 		u32 pg_offset;
 		u32 bytes_left = PAGE_SIZE;
@@ -175,12 +171,11 @@ static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio,
 		/* Hash through the page sector by sector */
 		for (pg_offset = 0; pg_offset < bytes_left;
 		     pg_offset += sectorsize) {
-			kaddr = kmap_atomic(page);
+			int ret;
-			crypto_shash_digest(shash, kaddr + pg_offset,
-					    sectorsize, csum);
-			kunmap_atomic(kaddr);
 
-			if (memcmp(&csum, cb_sum, csum_size) != 0) {
+			ret = btrfs_check_sector_csum(fs_info, page, pg_offset,
+						      csum, cb_sum);
+			if (ret) {
 				btrfs_print_data_csum_error(inode, disk_start,
 						csum, cb_sum, cb->mirror_num);
 				if (btrfs_bio(bio)->device)

fs/btrfs/ctree.h

@@ -3253,6 +3253,8 @@ u64 btrfs_file_extent_end(const struct btrfs_path *path);
 /* inode.c */
 void btrfs_submit_data_bio(struct inode *inode, struct bio *bio,
 			   int mirror_num, enum btrfs_compression_type compress_type);
+int btrfs_check_sector_csum(struct btrfs_fs_info *fs_info, struct page *page,
+			    u32 pgoff, u8 *csum, const u8 * const csum_expected);
 unsigned int btrfs_verify_data_csum(struct btrfs_bio *bbio,
 				    u32 bio_offset, struct page *page,
 				    u64 start, u64 end);

fs/btrfs/inode.c

@@ -3328,6 +3328,29 @@ void btrfs_writepage_endio_finish_ordered(struct btrfs_inode *inode,
 				       finish_ordered_fn, uptodate);
 }
 
+/*
+ * Verify the checksum for a single sector without any extra action that depend
+ * on the type of I/O.
+ */
+int btrfs_check_sector_csum(struct btrfs_fs_info *fs_info, struct page *page,
+			    u32 pgoff, u8 *csum, const u8 * const csum_expected)
+{
+	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
+	char *kaddr;
+
+	ASSERT(pgoff + fs_info->sectorsize <= PAGE_SIZE);
+
+	shash->tfm = fs_info->csum_shash;
+
+	kaddr = kmap_local_page(page) + pgoff;
+	crypto_shash_digest(shash, kaddr, fs_info->sectorsize, csum);
+	kunmap_local(kaddr);
+
+	if (memcmp(csum, csum_expected, fs_info->csum_size))
+		return -EIO;
+	return 0;
+}
+
 /*
  * check_data_csum - verify checksum of one sector of uncompressed data
  * @inode:	inode
@@ -3338,14 +3361,15 @@ void btrfs_writepage_endio_finish_ordered(struct btrfs_inode *inode,
  * @start:	logical offset in the file
  *
  * The length of such check is always one sector size.
+ *
+ * When csum mismatch is detected, we will also report the error and fill the
+ * corrupted range with zero. (Thus it needs the extra parameters)
  */
 static int check_data_csum(struct inode *inode, struct btrfs_bio *bbio,
 			   u32 bio_offset, struct page *page, u32 pgoff,
 			   u64 start)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
-	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
-	char *kaddr;
 	u32 len = fs_info->sectorsize;
 	const u32 csum_size = fs_info->csum_size;
 	unsigned int offset_sectors;
@@ -3357,16 +3381,10 @@ static int check_data_csum(struct inode *inode, struct btrfs_bio *bbio,
 	offset_sectors = bio_offset >> fs_info->sectorsize_bits;
 	csum_expected = ((u8 *)bbio->csum) + offset_sectors * csum_size;
 
-	kaddr = kmap_atomic(page);
+	if (btrfs_check_sector_csum(fs_info, page, pgoff, csum, csum_expected))
-	shash->tfm = fs_info->csum_shash;
-
-	crypto_shash_digest(shash, kaddr + pgoff, len, csum);
-	kunmap_atomic(kaddr);
-
-	if (memcmp(csum, csum_expected, csum_size))
 		goto zeroit;
-
 	return 0;
+
 zeroit:
 	btrfs_print_data_csum_error(BTRFS_I(inode), start, csum, csum_expected,
 				    bbio->mirror_num);