btrfs: fix two misuses of folio_shift()

It is meaningless to shift a byte count by folio_shift().  The folio index
is in units of PAGE_SIZE, not folio_size().  We can use folio_contains()
to make this work for arbitrary-order folios, so remove the assertion
that the folios are of order 0.

Reviewed-by: Qu Wenruo <[email protected]>
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: Matthew Wilcox (Oracle)

fs/btrfs/extent_io.c

@@ -523,8 +523,6 @@ static void end_bbio_data_read(struct btrfs_bio *bbio)
 		u64 end;
 		u32 len;
 
-		/* For now only order 0 folios are supported for data. */
-		ASSERT(folio_order(folio) == 0);
 		btrfs_debug(fs_info,
 			"%s: bi_sector=%llu, err=%d, mirror=%u",
 			__func__, bio->bi_iter.bi_sector, bio->bi_status,
@@ -552,7 +550,6 @@ static void end_bbio_data_read(struct btrfs_bio *bbio)
 
 		if (likely(uptodate)) {
 			loff_t i_size = i_size_read(inode);
-			pgoff_t end_index = i_size >> folio_shift(folio);
 
 			/*
 			 * Zero out the remaining part if this range straddles
@@ -561,9 +558,11 @@ static void end_bbio_data_read(struct btrfs_bio *bbio)
 			 * Here we should only zero the range inside the folio,
 			 * not touch anything else.
 			 *
-			 * NOTE: i_size is exclusive while end is inclusive.
+			 * NOTE: i_size is exclusive while end is inclusive and
+			 * folio_contains() takes PAGE_SIZE units.
 			 */
-			if (folio_index(folio) == end_index && i_size <= end) {
+			if (folio_contains(folio, i_size >> PAGE_SHIFT) &&
+			    i_size <= end) {
 				u32 zero_start = max(offset_in_folio(folio, i_size),
 						     offset_in_folio(folio, start));
 				u32 zero_len = offset_in_folio(folio, end) + 1 -
@@ -956,7 +955,7 @@ static int btrfs_do_readpage(struct folio *folio, struct extent_map **em_cached,
 		return ret;
 	}
 
-	if (folio->index == last_byte >> folio_shift(folio)) {
+	if (folio_contains(folio, last_byte >> PAGE_SHIFT)) {
 		size_t zero_offset = offset_in_folio(folio, last_byte);
 
 		if (zero_offset) {