[PATCH][next] ext4: Avoid -Wflex-array-member-not-at-end warning

Gustavo A. R. Silva
2025-03-26T22:55:54Z

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

Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition 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/ext4/mballoc.c:3041:40: 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>
---
fs/ext4/mballoc.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 0d523e9fb3d5..f88424c28194 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3037,10 +3037,8 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
unsigned char blocksize_bits = min_t(unsigned char,
sb->s_blocksize_bits,
EXT4_MAX_BLOCK_LOG_SIZE);
- struct sg {
- struct ext4_group_info info;
- ext4_grpblk_t counters[EXT4_MAX_BLOCK_LOG_SIZE + 2];
- } sg;
+ DEFINE_RAW_FLEX(struct ext4_group_info, sg, bb_counters,
+ EXT4_MAX_BLOCK_LOG_SIZE + 2);

group--;
if (group == 0)
@@ -3048,7 +3046,7 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
" 2^0 2^1 2^2 2^3 2^4 2^5 2^6 "
" 2^7 2^8 2^9 2^10 2^11 2^12 2^13 ]\n");

- i = (blocksize_bits + 2) * sizeof(sg.info.bb_counters[0]) +
+ i = (blocksize_bits + 2) * sizeof(sg->bb_counters[0]) +
sizeof(struct ext4_group_info);

grinfo = ext4_get_group_info(sb, group);
@@ -3068,14 +3066,14 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
* We care only about free space counters in the group info and
* these are safe to access even after the buddy has been unloaded
*/
- memcpy(&sg, grinfo, i);
- seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,
- sg.info.bb_fragments, sg.info.bb_first_free);
+ memcpy(sg, grinfo, i);
+ seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg->bb_free,
+ sg->bb_fragments, sg->bb_first_free);
for (i = 0; i <= 13; i++)
seq_printf(seq, " %-5u", i <= blocksize_bits + 1 ?
- sg.info.bb_counters[i] : 0);
+ sg->bb_counters[i] : 0);
seq_puts(seq, " ]");
- if (EXT4_MB_GRP_BBITMAP_CORRUPT(&sg.info))
+ if (EXT4_MB_GRP_BBITMAP_CORRUPT(sg))
seq_puts(seq, " Block bitmap corrupted!");
seq_putc(seq, '\n');
return 0;
--
2.43.0