[RFC v2 02/11] fs/buffer: add a for_each_bh() for block_read_full_folio()

[Luis Chamberlain <mcgrof@kernel.org>]

We want to be able to work through all buffer heads on a folio
for an async read, but in the future we want to support the option
to stop before we've processed all linked buffer heads. To make
code easier to read and follow adopt a for_each_bh(tmp, head) loop
instead of using a do { ... } while () to make the code easier to
read and later be expanded in subsequent patches.

This introduces no functional changes.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
 fs/buffer.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 580451337efa..108e1c36fc1a 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2392,6 +2392,17 @@ static void bh_read_batch_async(struct folio *folio,
 	}
 }
 
+#define bh_is_last(__bh, __head) ((__bh)->b_this_page == (__head))
+
+#define bh_next(__bh, __head) \
+    (bh_is_last(__bh, __head) ? NULL : (__bh)->b_this_page)
+
+/* Starts from the provided head */
+#define for_each_bh(__tmp, __head)			\
+    for ((__tmp) = (__head);				\
+         (__tmp);					\
+         (__tmp) = bh_next(__tmp, __head))
+
 /*
  * Generic "read_folio" function for block devices that have the normal
  * get_block functionality. This is most of the block device filesystems.
@@ -2421,11 +2432,10 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
 
 	iblock = div_u64(folio_pos(folio), blocksize);
 	lblock = div_u64(limit + blocksize - 1, blocksize);
-	bh = head;
 	nr = 0;
 	i = 0;
 
-	do {
+	for_each_bh(bh, head) {
 		if (buffer_uptodate(bh))
 			continue;
 
@@ -2454,7 +2464,9 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
 				continue;
 		}
 		arr[nr++] = bh;
-	} while (i++, iblock++, (bh = bh->b_this_page) != head);
+		i++;
+		iblock++;
+	}
 
 	bh_read_batch_async(folio, nr, arr, fully_mapped, nr == 0, page_error);
 
-- 
2.43.0