[PATCH v2] iomap: Break build if io_inline_bio is not last in iomap_ioend

[PATCH v2] iomap: Break build if io_inline_bio is not last in iomap_ioend

[Nikolay Borisov]

Comments are good but unfortunately they can't effectively enforce
certain invariants, to that effect let's break the build in case
io_inline_bio is, for whatever reason, not the last member of
iomap_ioend.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---

V2:
 - Fix indentation and long lines

 fs/iomap/buffered-io.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 9023717c5188..62e27faacc6e 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1225,6 +1225,9 @@ iomap_alloc_ioend(struct inode *inode, struct iomap_writepage_ctx *wpc,
 	bio->bi_write_hint = inode->i_write_hint;
 	wbc_init_bio(wbc, bio);

+	BUILD_BUG_ON(offsetof(struct iomap_ioend, io_inline_bio) +
+		     sizeof(struct bio) != sizeof(struct iomap_ioend));
+
 	ioend = container_of(bio, struct iomap_ioend, io_inline_bio);
 	INIT_LIST_HEAD(&ioend->io_list);
 	ioend->io_type = wpc->iomap.type;
--
2.25.1

Re: [PATCH v2] iomap: Break build if io_inline_bio is not last in iomap_ioend

[Christoph Hellwig]

On Tue, Jun 29, 2021 at 10:20:51AM +0300, Nikolay Borisov wrote:
> Comments are good but unfortunately they can't effectively enforce
> certain invariants, to that effect let's break the build in case
> io_inline_bio is, for whatever reason, not the last member of
> iomap_ioend.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>