[PATCH 0/8][next] Avoid a couple hundred -Wflex-array-member-not-at-end warnings

[PATCH 0/8][next] Avoid a couple hundred -Wflex-array-member-not-at-end warnings

[Gustavo A. R. Silva]

This patch series aims to fix a couple hundred -Wflex-array-member-not-at-end
warnings by creating a new tagged struct `struct bio_hdr` within flexible
structure `struct bio`.

This new tagged struct will be used to fix problematic declarations
of middle-flex-arrays in composite structs, like these[1][2][3], for
instance.

[1] https://git.kernel.org/linus/a7e8997ae18c42d3
[2] https://git.kernel.org/linus/c1ddb29709e675ea
[3] https://git.kernel.org/linus/57be3d3562ca4aa6

Gustavo A. R. Silva (8):
  block: blk_types.h: Use struct_group_tagged() in flex struct bio
  md/raid5-ppl: Avoid -Wflex-array-member-not-at-end warning
  xfs: Avoid -Wflex-array-member-not-at-end warnings
  erofs: Avoid -Wflex-array-member-not-at-end warnings
  btrfs: Avoid -Wflex-array-member-not-at-end warnings
  nvme: target: Avoid -Wflex-array-member-not-at-end warnings
  md/raid5: Avoid -Wflex-array-member-not-at-end warnings
  bcache: Avoid -Wflex-array-member-not-at-end warnings

 drivers/md/bcache/bcache.h     |  4 +-
 drivers/md/bcache/journal.c    | 10 ++--
 drivers/md/bcache/journal.h    |  4 +-
 drivers/md/bcache/super.c      |  8 ++--
 drivers/md/raid5-ppl.c         |  8 ++--
 drivers/md/raid5.c             | 10 ++--
 drivers/md/raid5.h             |  2 +-
 drivers/nvme/target/nvmet.h    |  4 +-
 drivers/nvme/target/passthru.c |  2 +-
 drivers/nvme/target/zns.c      |  2 +-
 fs/btrfs/disk-io.c             |  4 +-
 fs/btrfs/volumes.h             |  2 +-
 fs/erofs/fileio.c              | 25 ++++++----
 fs/erofs/fscache.c             | 13 +++---
 fs/xfs/xfs_log.c               | 15 +++---
 fs/xfs/xfs_log_priv.h          |  2 +-
 include/linux/blk_types.h      | 84 ++++++++++++++++++----------------
 17 files changed, 107 insertions(+), 92 deletions(-)

-- 
2.43.0

[PATCH 8/8][next] bcache: Avoid -Wflex-array-member-not-at-end warnings

[Gustavo A. R. Silva]

-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 members 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 112 of the following warnings:

drivers/md/bcache/bcache.h:233:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/md/bcache/bcache.h:241:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/md/bcache/bcache.h:242:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/md/bcache/bcache.h:308:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/md/bcache/bcache.h:422:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/md/bcache/bcache.h:639:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/md/bcache/journal.h:152:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/md/bcache/journal.h:156:33: 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 <gustavoars@kernel.org>
---
 drivers/md/bcache/bcache.h  |  4 ++--
 drivers/md/bcache/journal.c | 10 +++++-----
 drivers/md/bcache/journal.h |  4 ++--
 drivers/md/bcache/super.c   |  8 +++++---
 4 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 785b0d9008fa..328023e90eb2 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -305,7 +305,7 @@ struct cached_dev {
 
 	struct cache_sb		sb;
 	struct cache_sb_disk	*sb_disk;
-	struct bio		sb_bio;
+	struct bio_hdr		sb_bio;
 	struct bio_vec		sb_bv[1];
 	struct closure		sb_write;
 	struct semaphore	sb_write_mutex;
@@ -419,7 +419,7 @@ struct cache {
 	struct cache_set	*set;
 	struct cache_sb		sb;
 	struct cache_sb_disk	*sb_disk;
-	struct bio		sb_bio;
+	struct bio_hdr		sb_bio;
 	struct bio_vec		sb_bv[1];
 
 	struct kobject		kobj;
diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index 7ff14bd2feb8..2ead129f7758 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -36,7 +36,7 @@ static int journal_read_bucket(struct cache *ca, struct list_head *list,
 			       unsigned int bucket_index)
 {
 	struct journal_device *ja = &ca->journal;
-	struct bio *bio = &ja->bio;
+	struct bio *bio = container_of(&ja->bio, struct bio, __hdr);
 
 	struct journal_replay *i;
 	struct jset *j, *data = ca->set->journal.w[0].data;
@@ -571,7 +571,7 @@ static void btree_flush_write(struct cache_set *c)
 static void journal_discard_endio(struct bio *bio)
 {
 	struct journal_device *ja =
-		container_of(bio, struct journal_device, discard_bio);
+		container_of(&bio->__hdr, struct journal_device, discard_bio);
 	struct cache *ca = container_of(ja, struct cache, journal);
 
 	atomic_set(&ja->discard_in_flight, DISCARD_DONE);
@@ -585,13 +585,13 @@ static void journal_discard_work(struct work_struct *work)
 	struct journal_device *ja =
 		container_of(work, struct journal_device, discard_work);
 
-	submit_bio(&ja->discard_bio);
+	submit_bio(container_of(&ja->discard_bio, struct bio, __hdr));
 }
 
 static void do_journal_discard(struct cache *ca)
 {
 	struct journal_device *ja = &ca->journal;
-	struct bio *bio = &ja->discard_bio;
+	struct bio *bio = container_of(&ja->discard_bio, struct bio, __hdr);
 
 	if (!ca->discard) {
 		ja->discard_idx = ja->last_idx;
@@ -787,7 +787,7 @@ static CLOSURE_CALLBACK(journal_write_unlocked)
 
 	for (i = 0; i < KEY_PTRS(k); i++) {
 		ca = c->cache;
-		bio = &ca->journal.bio;
+		bio = container_of(&ca->journal.bio, struct bio, __hdr);
 
 		atomic_long_add(sectors, &ca->meta_sectors_written);
 
diff --git a/drivers/md/bcache/journal.h b/drivers/md/bcache/journal.h
index cd316b4a1e95..b4ff5269aee3 100644
--- a/drivers/md/bcache/journal.h
+++ b/drivers/md/bcache/journal.h
@@ -149,11 +149,11 @@ struct journal_device {
 	atomic_t		discard_in_flight;
 
 	struct work_struct	discard_work;
-	struct bio		discard_bio;
+	struct bio_hdr		discard_bio;
 	struct bio_vec		discard_bv;
 
 	/* Bio for journal reads/writes to this device */
-	struct bio		bio;
+	struct bio_hdr		bio;
 	struct bio_vec		bv[8];
 };
 
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index e42f1400cea9..cd1342355cf2 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -337,7 +337,7 @@ static CLOSURE_CALLBACK(bch_write_bdev_super_unlock)
 void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent)
 {
 	struct closure *cl = &dc->sb_write;
-	struct bio *bio = &dc->sb_bio;
+	struct bio *bio = container_of(&dc->sb_bio, struct bio, __hdr);
 
 	down(&dc->sb_write_mutex);
 	closure_init(cl, parent);
@@ -374,7 +374,7 @@ void bcache_write_super(struct cache_set *c)
 {
 	struct closure *cl = &c->sb_write;
 	struct cache *ca = c->cache;
-	struct bio *bio = &ca->sb_bio;
+	struct bio *bio = container_of(&ca->sb_bio, struct bio, __hdr);
 	unsigned int version = BCACHE_SB_VERSION_CDEV_WITH_UUID;
 
 	down(&c->sb_write_mutex);
@@ -2230,7 +2230,9 @@ static int cache_alloc(struct cache *ca)
 	__module_get(THIS_MODULE);
 	kobject_init(&ca->kobj, &bch_cache_ktype);
 
-	bio_init(&ca->journal.bio, NULL, ca->journal.bio.bi_inline_vecs, 8, 0);
+	bio_init(container_of(&ca->journal.bio, struct bio, __hdr), NULL,
+		 container_of(&ca->journal.bio, struct bio, __hdr)->bi_inline_vecs,
+		 8, 0);
 
 	/*
 	 * when ca->sb.njournal_buckets is not zero, journal exists,
-- 
2.43.0

Re: [PATCH 8/8][next] bcache: Avoid -Wflex-array-member-not-at-end warnings

[Coly Li]

On Mon, Feb 24, 2025 at 08:31:26PM +0800, Gustavo A. R. Silva wrote:
> -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 members 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 112 of the following warnings:
> 
> drivers/md/bcache/bcache.h:233:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:241:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:242:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:308:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:422:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:639:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/journal.h:152:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/journal.h:156:33: 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 <gustavoars@kernel.org>

Hi Gustavo,

each struct bio followed by a struct bio_vec at the location where
struct bio is embedded into middle of a structure. So the general
flex-array-in-middle issue doesn't exist here indeed.

I don't suggest to introduce extra complication in bcache code.

How about to improve the checking script, if there is no following
struct bio_vec after struct bio, then that should be something really
suspicious.

Thanks.

Coly Li

> ---
>  drivers/md/bcache/bcache.h  |  4 ++--
>  drivers/md/bcache/journal.c | 10 +++++-----
>  drivers/md/bcache/journal.h |  4 ++--
>  drivers/md/bcache/super.c   |  8 +++++---
>  4 files changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 785b0d9008fa..328023e90eb2 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -305,7 +305,7 @@ struct cached_dev {
>  
>  	struct cache_sb		sb;
>  	struct cache_sb_disk	*sb_disk;
> -	struct bio		sb_bio;
> +	struct bio_hdr		sb_bio;
>  	struct bio_vec		sb_bv[1];
>  	struct closure		sb_write;
>  	struct semaphore	sb_write_mutex;
> @@ -419,7 +419,7 @@ struct cache {
>  	struct cache_set	*set;
>  	struct cache_sb		sb;
>  	struct cache_sb_disk	*sb_disk;
> -	struct bio		sb_bio;
> +	struct bio_hdr		sb_bio;
>  	struct bio_vec		sb_bv[1];
>  
>  	struct kobject		kobj;
> diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
> index 7ff14bd2feb8..2ead129f7758 100644
> --- a/drivers/md/bcache/journal.c
> +++ b/drivers/md/bcache/journal.c
> @@ -36,7 +36,7 @@ static int journal_read_bucket(struct cache *ca, struct list_head *list,
>  			       unsigned int bucket_index)
>  {
>  	struct journal_device *ja = &ca->journal;
> -	struct bio *bio = &ja->bio;
> +	struct bio *bio = container_of(&ja->bio, struct bio, __hdr);
>  
>  	struct journal_replay *i;
>  	struct jset *j, *data = ca->set->journal.w[0].data;
> @@ -571,7 +571,7 @@ static void btree_flush_write(struct cache_set *c)
>  static void journal_discard_endio(struct bio *bio)
>  {
>  	struct journal_device *ja =
> -		container_of(bio, struct journal_device, discard_bio);
> +		container_of(&bio->__hdr, struct journal_device, discard_bio);
>  	struct cache *ca = container_of(ja, struct cache, journal);
>  
>  	atomic_set(&ja->discard_in_flight, DISCARD_DONE);
> @@ -585,13 +585,13 @@ static void journal_discard_work(struct work_struct *work)
>  	struct journal_device *ja =
>  		container_of(work, struct journal_device, discard_work);
>  
> -	submit_bio(&ja->discard_bio);
> +	submit_bio(container_of(&ja->discard_bio, struct bio, __hdr));
>  }
>  
>  static void do_journal_discard(struct cache *ca)
>  {
>  	struct journal_device *ja = &ca->journal;
> -	struct bio *bio = &ja->discard_bio;
> +	struct bio *bio = container_of(&ja->discard_bio, struct bio, __hdr);
>  
>  	if (!ca->discard) {
>  		ja->discard_idx = ja->last_idx;
> @@ -787,7 +787,7 @@ static CLOSURE_CALLBACK(journal_write_unlocked)
>  
>  	for (i = 0; i < KEY_PTRS(k); i++) {
>  		ca = c->cache;
> -		bio = &ca->journal.bio;
> +		bio = container_of(&ca->journal.bio, struct bio, __hdr);
>  
>  		atomic_long_add(sectors, &ca->meta_sectors_written);
>  
> diff --git a/drivers/md/bcache/journal.h b/drivers/md/bcache/journal.h
> index cd316b4a1e95..b4ff5269aee3 100644
> --- a/drivers/md/bcache/journal.h
> +++ b/drivers/md/bcache/journal.h
> @@ -149,11 +149,11 @@ struct journal_device {
>  	atomic_t		discard_in_flight;
>  
>  	struct work_struct	discard_work;
> -	struct bio		discard_bio;
> +	struct bio_hdr		discard_bio;
>  	struct bio_vec		discard_bv;
>  
>  	/* Bio for journal reads/writes to this device */
> -	struct bio		bio;
> +	struct bio_hdr		bio;
>  	struct bio_vec		bv[8];
>  };
>  
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index e42f1400cea9..cd1342355cf2 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -337,7 +337,7 @@ static CLOSURE_CALLBACK(bch_write_bdev_super_unlock)
>  void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent)
>  {
>  	struct closure *cl = &dc->sb_write;
> -	struct bio *bio = &dc->sb_bio;
> +	struct bio *bio = container_of(&dc->sb_bio, struct bio, __hdr);
>  
>  	down(&dc->sb_write_mutex);
>  	closure_init(cl, parent);
> @@ -374,7 +374,7 @@ void bcache_write_super(struct cache_set *c)
>  {
>  	struct closure *cl = &c->sb_write;
>  	struct cache *ca = c->cache;
> -	struct bio *bio = &ca->sb_bio;
> +	struct bio *bio = container_of(&ca->sb_bio, struct bio, __hdr);
>  	unsigned int version = BCACHE_SB_VERSION_CDEV_WITH_UUID;
>  
>  	down(&c->sb_write_mutex);
> @@ -2230,7 +2230,9 @@ static int cache_alloc(struct cache *ca)
>  	__module_get(THIS_MODULE);
>  	kobject_init(&ca->kobj, &bch_cache_ktype);
>  
> -	bio_init(&ca->journal.bio, NULL, ca->journal.bio.bi_inline_vecs, 8, 0);
> +	bio_init(container_of(&ca->journal.bio, struct bio, __hdr), NULL,
> +		 container_of(&ca->journal.bio, struct bio, __hdr)->bi_inline_vecs,
> +		 8, 0);
>  
>  	/*
>  	 * when ca->sb.njournal_buckets is not zero, journal exists,
> -- 
> 2.43.0
> 

-- 
Coly Li