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Message-ID: <gynmaxokdg2t73okjvtl7cuvlcfa5saqwdnd3jh5obwejzy3ce@ic3q4nkrozlr>
Date: Wed, 30 Apr 2025 14:32:33 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] bcachefs: Avoid -Wflex-array-member-not-at-end
warning
On Wed, Apr 30, 2025 at 12:27:26PM -0600, Gustavo A. R. Silva wrote:
>
>
> On 29/04/25 19:40, Kent Overstreet wrote:
> > On Tue, Apr 29, 2025 at 07:15:37PM -0600, 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.
> > >
> > > Use the `DEFINE_FLEX()` helper for on-stack definitions of a flexible
> > > structure where the size of the flexible-array member is known at
> > > compile-time, and refactor the rest of the code, accordingly.
> > >
> > > So, with these changes, fix the following warning:
> > >
> > > fs/bcachefs/disk_accounting.c:429:51: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> >
> > We also have bch_replicas_padded, does that also need a fix?
>
> Yes - so, how about the following to address both issues:
Yes, I like that much better
>
> diff --git a/fs/bcachefs/disk_accounting.c b/fs/bcachefs/disk_accounting.c
> index 7be71952425c..2dcccf1edbb9 100644
> --- a/fs/bcachefs/disk_accounting.c
> +++ b/fs/bcachefs/disk_accounting.c
> @@ -287,7 +287,7 @@ static inline bool accounting_to_replicas(struct bch_replicas_entry_v1 *r, struc
>
> static int bch2_accounting_update_sb_one(struct bch_fs *c, struct bpos p)
> {
> - struct bch_replicas_padded r;
> + union bch_replicas_padded r;
> return accounting_to_replicas(&r.e, p)
> ? bch2_mark_replicas(c, &r.e)
> : 0;
> @@ -361,7 +361,7 @@ static int __bch2_accounting_mem_insert(struct bch_fs *c, struct bkey_s_c_accoun
> int bch2_accounting_mem_insert(struct bch_fs *c, struct bkey_s_c_accounting a,
> enum bch_accounting_mode mode)
> {
> - struct bch_replicas_padded r;
> + union bch_replicas_padded r;
>
> if (mode != BCH_ACCOUNTING_read &&
> accounting_to_replicas(&r.e, a.k->p) &&
> @@ -425,10 +425,12 @@ int bch2_fs_replicas_usage_read(struct bch_fs *c, darray_char *usage)
>
> percpu_down_read(&c->mark_lock);
> darray_for_each(acc->k, i) {
> - struct {
> + union {
> + u8 bytes[struct_size_t(struct bch_replicas_usage, r.devs,
> + BCH_BKEY_PTRS_MAX)];
> struct bch_replicas_usage r;
> - u8 pad[BCH_BKEY_PTRS_MAX];
> } u;
> + u.r.r.nr_devs = BCH_BKEY_PTRS_MAX;
>
> if (!accounting_to_replicas(&u.r.r, i->pos))
> continue;
> @@ -627,7 +629,7 @@ static int bch2_disk_accounting_validate_late(struct btree_trans *trans,
>
> switch (acc->type) {
> case BCH_DISK_ACCOUNTING_replicas: {
> - struct bch_replicas_padded r;
> + union bch_replicas_padded r;
> __accounting_to_replicas(&r.e, acc);
>
> for (unsigned i = 0; i < r.e.nr_devs; i++)
> diff --git a/fs/bcachefs/ec_types.h b/fs/bcachefs/ec_types.h
> index 06144bfd9c19..809446c78951 100644
> --- a/fs/bcachefs/ec_types.h
> +++ b/fs/bcachefs/ec_types.h
> @@ -4,9 +4,10 @@
>
> #include "bcachefs_format.h"
>
> -struct bch_replicas_padded {
> +union bch_replicas_padded {
> + u8 bytes[struct_size_t(struct bch_replicas_entry_v1,
> + devs, BCH_BKEY_PTRS_MAX)];
> struct bch_replicas_entry_v1 e;
> - u8 pad[BCH_BKEY_PTRS_MAX];
> };
>
> struct stripe {
> @@ -28,7 +29,7 @@ struct gc_stripe {
> u16 block_sectors[BCH_BKEY_PTRS_MAX];
> struct bch_extent_ptr ptrs[BCH_BKEY_PTRS_MAX];
>
> - struct bch_replicas_padded r;
> + union bch_replicas_padded r;
> };
>
> #endif /* _BCACHEFS_EC_TYPES_H */
> diff --git a/fs/bcachefs/journal_io.c b/fs/bcachefs/journal_io.c
> index 58e3983d860a..7c09a3c109ab 100644
> --- a/fs/bcachefs/journal_io.c
> +++ b/fs/bcachefs/journal_io.c
> @@ -1404,7 +1404,7 @@ int bch2_journal_read(struct bch_fs *c,
> }
>
> genradix_for_each(&c->journal_entries, radix_iter, _i) {
> - struct bch_replicas_padded replicas = {
> + union bch_replicas_padded replicas = {
> .e.data_type = BCH_DATA_journal,
> .e.nr_devs = 0,
> .e.nr_required = 1,
> @@ -1632,7 +1632,7 @@ static CLOSURE_CALLBACK(journal_write_done)
> closure_type(w, struct journal_buf, io);
> struct journal *j = container_of(w, struct journal, buf[w->idx]);
> struct bch_fs *c = container_of(j, struct bch_fs, journal);
> - struct bch_replicas_padded replicas;
> + union bch_replicas_padded replicas;
> u64 seq = le64_to_cpu(w->data->seq);
> int err = 0;
>
> @@ -2055,7 +2055,7 @@ CLOSURE_CALLBACK(bch2_journal_write)
> closure_type(w, struct journal_buf, io);
> struct journal *j = container_of(w, struct journal, buf[w->idx]);
> struct bch_fs *c = container_of(j, struct bch_fs, journal);
> - struct bch_replicas_padded replicas;
> + union bch_replicas_padded replicas;
> unsigned nr_rw_members = dev_mask_nr(&c->rw_devs[BCH_DATA_journal]);
> int ret;
>
> diff --git a/fs/bcachefs/journal_reclaim.c b/fs/bcachefs/journal_reclaim.c
> index 66bfb95f1ea4..0acaf20f2181 100644
> --- a/fs/bcachefs/journal_reclaim.c
> +++ b/fs/bcachefs/journal_reclaim.c
> @@ -953,7 +953,7 @@ int bch2_journal_flush_device_pins(struct journal *j, int dev_idx)
> seq = 0;
> spin_lock(&j->lock);
> while (!ret) {
> - struct bch_replicas_padded replicas;
> + union bch_replicas_padded replicas;
>
> seq = max(seq, journal_last_seq(j));
> if (seq >= j->pin.back)
>
>
> Thanks
> -Gustavo
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