-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Change the type of the middle struct member currently causing trouble from
`struct bio` to `struct bio_hdr`.

We also use `container_of()` whenever we need to retrieve a pointer to
the flexible structure `struct bio`, through which we can access the
flexible-array member in it, if necessary.

With these changes fix the following warnings:
fs/erofs/fileio.c:10:20: warning: structure containing a flexible array member 
is not at the end of another structure [-Wflex-array-member-not-at-end]
fs/erofs/fscache.c:179:20: warning: structure containing a flexible array 
member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavo...@kernel.org>
---
 fs/erofs/fileio.c  | 25 +++++++++++++++----------
 fs/erofs/fscache.c | 13 +++++++------
 2 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/fs/erofs/fileio.c b/fs/erofs/fileio.c
index 0ffd1c63beeb..3080963caf78 100644
--- a/fs/erofs/fileio.c
+++ b/fs/erofs/fileio.c
@@ -7,7 +7,7 @@
 
 struct erofs_fileio_rq {
        struct bio_vec bvecs[16];
-       struct bio bio;
+       struct bio_hdr bio;
        struct kiocb iocb;
        struct super_block *sb;
 };
@@ -26,20 +26,21 @@ static void erofs_fileio_ki_complete(struct kiocb *iocb, 
long ret)
 
        if (ret > 0) {
                if (ret != rq->bio.bi_iter.bi_size) {
-                       bio_advance(&rq->bio, ret);
-                       zero_fill_bio(&rq->bio);
+                       bio_advance(container_of(&rq->bio, struct bio, __hdr),
+                                   ret);
+                       zero_fill_bio(container_of(&rq->bio, struct bio, 
__hdr));
                }
                ret = 0;
        }
        if (rq->bio.bi_end_io) {
-               rq->bio.bi_end_io(&rq->bio);
+               rq->bio.bi_end_io(container_of(&rq->bio, struct bio, __hdr));
        } else {
-               bio_for_each_folio_all(fi, &rq->bio) {
+               bio_for_each_folio_all(fi, container_of(&rq->bio, struct bio, 
__hdr)) {
                        DBG_BUGON(folio_test_uptodate(fi.folio));
                        erofs_onlinefolio_end(fi.folio, ret);
                }
        }
-       bio_uninit(&rq->bio);
+       bio_uninit(container_of(&rq->bio, struct bio, __hdr));
        kfree(rq);
 }
 
@@ -68,7 +69,8 @@ static struct erofs_fileio_rq *erofs_fileio_rq_alloc(struct 
erofs_map_dev *mdev)
        struct erofs_fileio_rq *rq = kzalloc(sizeof(*rq),
                                             GFP_KERNEL | __GFP_NOFAIL);
 
-       bio_init(&rq->bio, NULL, rq->bvecs, ARRAY_SIZE(rq->bvecs), REQ_OP_READ);
+       bio_init(container_of(&rq->bio, struct bio, __hdr), NULL, rq->bvecs,
+                ARRAY_SIZE(rq->bvecs), REQ_OP_READ);
        rq->iocb.ki_filp = mdev->m_dif->file;
        rq->sb = mdev->m_sb;
        return rq;
@@ -76,12 +78,13 @@ static struct erofs_fileio_rq *erofs_fileio_rq_alloc(struct 
erofs_map_dev *mdev)
 
 struct bio *erofs_fileio_bio_alloc(struct erofs_map_dev *mdev)
 {
-       return &erofs_fileio_rq_alloc(mdev)->bio;
+       return container_of(&erofs_fileio_rq_alloc(mdev)->bio, struct bio, 
__hdr);
 }
 
 void erofs_fileio_submit_bio(struct bio *bio)
 {
-       return erofs_fileio_rq_submit(container_of(bio, struct erofs_fileio_rq,
+       return erofs_fileio_rq_submit(container_of(&bio->__hdr,
+                                                  struct erofs_fileio_rq,
                                                   bio));
 }
 
@@ -150,7 +153,9 @@ static int erofs_fileio_scan_folio(struct erofs_fileio *io, 
struct folio *folio)
                        }
                        if (!attached++)
                                erofs_onlinefolio_split(folio);
-                       if (!bio_add_folio(&io->rq->bio, folio, len, cur))
+                       if (!bio_add_folio(container_of(&io->rq->bio,
+                                                       struct bio, __hdr),
+                                          folio, len, cur))
                                goto io_retry;
                        io->dev.m_pa += len;
                }
diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index ce3d8737df85..719ec96c8f22 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -176,7 +176,7 @@ static int erofs_fscache_read_io_async(struct 
fscache_cookie *cookie,
 
 struct erofs_fscache_bio {
        struct erofs_fscache_io io;
-       struct bio bio;         /* w/o bdev to share bio_add_page/endio() */
+       struct bio_hdr bio;     /* w/o bdev to share bio_add_page/endio() */
        struct bio_vec bvecs[BIO_MAX_VECS];
 };
 
@@ -187,7 +187,7 @@ static void erofs_fscache_bio_endio(void *priv,
 
        if (IS_ERR_VALUE(transferred_or_error))
                io->bio.bi_status = errno_to_blk_status(transferred_or_error);
-       io->bio.bi_end_io(&io->bio);
+       io->bio.bi_end_io(container_of(&io->bio, struct bio, __hdr));
        BUILD_BUG_ON(offsetof(struct erofs_fscache_bio, io) != 0);
        erofs_fscache_io_put(&io->io);
 }
@@ -197,17 +197,18 @@ struct bio *erofs_fscache_bio_alloc(struct erofs_map_dev 
*mdev)
        struct erofs_fscache_bio *io;
 
        io = kmalloc(sizeof(*io), GFP_KERNEL | __GFP_NOFAIL);
-       bio_init(&io->bio, NULL, io->bvecs, BIO_MAX_VECS, REQ_OP_READ);
+       bio_init(container_of(&io->bio, struct bio, __hdr), NULL, io->bvecs,
+                BIO_MAX_VECS, REQ_OP_READ);
        io->io.private = mdev->m_dif->fscache->cookie;
        io->io.end_io = erofs_fscache_bio_endio;
        refcount_set(&io->io.ref, 1);
-       return &io->bio;
+       return container_of(&io->bio, struct bio, __hdr);
 }
 
 void erofs_fscache_submit_bio(struct bio *bio)
 {
-       struct erofs_fscache_bio *io = container_of(bio,
-                       struct erofs_fscache_bio, bio);
+       struct erofs_fscache_bio *io =
+               container_of(&bio->__hdr, struct erofs_fscache_bio, bio);
        int ret;
 
        iov_iter_bvec(&io->io.iter, ITER_DEST, io->bvecs, bio->bi_vcnt,
-- 
2.43.0

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