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SubjectRe: [PATCH] [v2] bcache: hide variable-sized types from uapi header check
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On 9/28/21 4:55 PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> The headers_check helper complains about a GNU extension in
> one of the exported headers:
>
> linux/bcache.h:354:2: warning: field '' with variable sized type 'union jset::(anonymous at ./usr/include/linux/bcache.h:354:2)' not at the end of a struct or class is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
> BKEY_PADDED(uuid_bucket);
> ^
> linux/bcache.h:134:2: note: expanded from macro 'BKEY_PADDED'
> union { struct bkey key; __u64 key ## _pad[BKEY_PAD]; }
> ^
>
> Address this by enclosing the GNU extensions in an #ifdef: Since the
> header check is done with --std=c90, this shuts up the warning and makes
> it possible to include the header file C90 user space applications, but
> allows applications built with --std=gnu89 or higher to use those
> parts.
>
> Another alternative would be to exclude this header from the check,
> but the GNU extension check seems more sensible.
>
> Fixes: 81ab4190ac17 ("bcache: Pull on disk data structures out into a separate header")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Hi Arnd,

IMHO, remove bcache related header from uapi check might be better
solution. So far only bcache-tools uses this header with its own copy,
no application includes the header(s) so far. It makes sense to exclude
bcache.h from upai headers check.

Thanks.

Coly Li

> ---
> v2: use __STRICT_ANSI__ check instead of __KERNEL__.
>
> I think this version is better than the first, let me know if that
> works for you.
> ---
> include/uapi/linux/bcache.h | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
> index cf7399f03b71..b7901e986193 100644
> --- a/include/uapi/linux/bcache.h
> +++ b/include/uapi/linux/bcache.h
> @@ -23,9 +23,13 @@ static inline void SET_##name(type *k, __u64 v) \
> struct bkey {
> __u64 high;
> __u64 low;
> +#ifndef __STRICT_ANSI__
> + /* gcc extension not meant for user space */
> __u64 ptr[];
> +#endif
> };
>
> +#ifndef __STRICT_ANSI__
> #define KEY_FIELD(name, field, offset, size) \
> BITMASK(name, struct bkey, field, offset, size)
>
> @@ -127,6 +131,8 @@ static inline struct bkey *bkey_idx(const struct bkey *k, unsigned int nr_keys)
>
> return (struct bkey *) (d + nr_keys);
> }
> +#endif
> +
> /* Enough for a key with 6 pointers */
> #define BKEY_PAD 8
>

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