[Drbd-dev] [PATCH][next] block: Replace zero-length array with flexible-array member

[Ilya Dryomov]

On Wed, Feb 26, 2020 at 12:45 AM Gustavo A. R. Silva
<gustavo at embeddedor.com> wrote:
>
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
>
> struct foo {
>         int stuff;
>         struct boo array[];
> };
>
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.
>
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
>
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
>
> This issue was found with the help of Coccinelle.
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com>
> ---
>  block/partitions/ldm.h             | 2 +-
>  drivers/block/drbd/drbd_int.h      | 2 +-
>  drivers/block/drbd/drbd_protocol.h | 8 ++++----

For rbd

>  drivers/block/rbd_types.h          | 2 +-

Acked-by: Ilya Dryomov <idryomov at gmail.com>

Thanks,

                Ilya