Re: [PATCH] net/ipv4: Fix error: type name requires a specifier or qualifier

[Yonghong Song <yhs@meta.com>]

On 11/10/22 7:17 AM, Rong Tao wrote:
> From: Rong Tao <rongtao@cestc.cn>
> 
> since commit 5854a09b4957("net/ipv4: Use __DECLARE_FLEX_ARRAY() helper")
> linux/in.h use __DECLARE_FLEX_ARRAY() macro, and sync to tools/ in commit
> 036b8f5b8970("tools headers uapi: Update linux/in.h copy"), this macro
> define in linux/stddef.h, which introduced in commit 3080ea5553cc("stddef:
> Introduce DECLARE_FLEX_ARRAY() helper"), thus, stddef.h should be included
> in in.h, which resolves the compilation error below:
> 
> How to reproduce this compilation error:
> 
> $ make -C tools/testing/selftests/bpf/
> In file included from progs/bpf_flow.c:8:
> linux/in.h:199:3: error: type name requires a specifier or qualifier
>                  __DECLARE_FLEX_ARRAY(__be32, imsf_slist_flex);
>                  ^
> linux/in.h:199:32: error: type specifier missing, defaults to 'int' [-Werror,-Wimplicit-int]
>                  __DECLARE_FLEX_ARRAY(__be32, imsf_slist_flex);
>                                               ^
> 2 errors generated.
> 
> Same error occurs with cgroup_skb_sk_lookup_kern.c, connect_force_port4.c,
> connect_force_port6.c, etc. that contain the header linux/in.h.

It has been fixed in bpf tree:
    https://lore.kernel.org/bpf/20221102182517.2675301-1-andrii@kernel.org/
The fix will be merged to bpf-next once it reached to linus tree and 
went back to bpf-next.

At the same time, you can workaround the issue locally.

> 
> Signed-off-by: Rong Tao <rongtao@cestc.cn>
> ---
>   include/uapi/linux/in.h       | 1 +
>   tools/include/uapi/linux/in.h | 1 +
>   2 files changed, 2 insertions(+)
> 
> diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
> index f243ce665f74..07a4cb149305 100644
> --- a/include/uapi/linux/in.h
> +++ b/include/uapi/linux/in.h
> @@ -20,6 +20,7 @@
>   #define _UAPI_LINUX_IN_H
>   
>   #include <linux/types.h>
> +#include <linux/stddef.h>
>   #include <linux/libc-compat.h>
>   #include <linux/socket.h>
>   
> diff --git a/tools/include/uapi/linux/in.h b/tools/include/uapi/linux/in.h
> index f243ce665f74..07a4cb149305 100644
> --- a/tools/include/uapi/linux/in.h
> +++ b/tools/include/uapi/linux/in.h
> @@ -20,6 +20,7 @@
>   #define _UAPI_LINUX_IN_H
>   
>   #include <linux/types.h>
> +#include <linux/stddef.h>
>   #include <linux/libc-compat.h>
>   #include <linux/socket.h>
>