bcachefs: Avoid -Wflex-array-member-not-at-end warning

-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]

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
 fs/bcachefs/disk_accounting.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

fs/bcachefs/disk_accounting.c +7 -9

index 7be71952425c..381e666679d2 100644
@@ -425,24 +425,22 @@ 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 {
-			struct bch_replicas_usage r;
-			u8 pad[BCH_BKEY_PTRS_MAX];
-		} u;
+		DEFINE_FLEX(struct bch_replicas_usage, u, r.devs, r.nr_devs,
+			    BCH_BKEY_PTRS_MAX);
 
-		if (!accounting_to_replicas(&u.r.r, i->pos))
+		if (!accounting_to_replicas(&u->r, i->pos))
 			continue;
 
 		u64 sectors;
 		bch2_accounting_mem_read_counters(acc, i - acc->k.data, &sectors, 1, false);
-		u.r.sectors = sectors;
+		u->sectors = sectors;
 
-		ret = darray_make_room(usage, replicas_usage_bytes(&u.r));
+		ret = darray_make_room(usage, replicas_usage_bytes(u));
 		if (ret)
 			break;
 
-		memcpy(&darray_top(*usage), &u.r, replicas_usage_bytes(&u.r));
-		usage->nr += replicas_usage_bytes(&u.r);
+		memcpy(&darray_top(*usage), u, replicas_usage_bytes(u));
+		usage->nr += replicas_usage_bytes(u);
 	}
 	percpu_up_read(&c->mark_lock);
 

Signature · 1 line

2.43.0

Quoted 7 lines · Gustavo A. R. Silva

-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.

Quoted 3 lines

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?

Quoted 8 lines · Kent Overstreet

Quoted 7 lines · Gustavo A. R. Silva

-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.

Quoted 5 lines

Quoted 3 lines

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:

fs/bcachefs/disk_accounting.c +7 -5

index 7be71952425c..2dcccf1edbb9 100644
@@ -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++)

fs/bcachefs/ec_types.h +4 -3

index 06144bfd9c19..809446c78951 100644
@@ -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 */

fs/bcachefs/journal_io.c +3 -3

index 58e3983d860a..7c09a3c109ab 100644
@@ -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;
 

fs/bcachefs/journal_reclaim.c +1 -1

index 66bfb95f1ea4..0acaf20f2181 100644
@@ -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