From: Gal Pressman <[email protected]>
Date: Wed, 12 Feb 2025 16:09:53 +0200
> Remove the hidden assumption that options are allocated at the end of
> the struct, and teach the compiler about them using a flexible array.
[...]
> diff --git a/include/net/dst_metadata.h b/include/net/dst_metadata.h
> index 84c15402931c..4160731dcb6e 100644
> --- a/include/net/dst_metadata.h
> +++ b/include/net/dst_metadata.h
> @@ -163,11 +163,8 @@ static inline struct metadata_dst
> *tun_dst_unclone(struct sk_buff *skb)
> if (!new_md)
> return ERR_PTR(-ENOMEM);
>
> - unsafe_memcpy(&new_md->u.tun_info, &md_dst->u.tun_info,
> - sizeof(struct ip_tunnel_info) + md_size,
> - /* metadata_dst_alloc() reserves room (md_size bytes) for
> - * options right after the ip_tunnel_info struct.
> - */);
> + memcpy(&new_md->u.tun_info, &md_dst->u.tun_info,
> + sizeof(struct ip_tunnel_info) + md_size);
> #ifdef CONFIG_DST_CACHE
> /* Unclone the dst cache if there is one */
> if (new_md->u.tun_info.dst_cache.cache) {
> diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
> index 1aa31bdb2b31..517f78070be0 100644
> --- a/include/net/ip_tunnels.h
> +++ b/include/net/ip_tunnels.h
> @@ -93,12 +93,6 @@ struct ip_tunnel_encap {
> GENMASK((sizeof_field(struct ip_tunnel_info, \
> options_len) * BITS_PER_BYTE) - 1, 0)
>
> -#define ip_tunnel_info_opts(info) \
> - _Generic(info, \
> - const struct ip_tunnel_info * : ((const void *)((info) + 1)),\
> - struct ip_tunnel_info * : ((void *)((info) + 1))\
> - )
You could leave this macro inplace and just change `(info) + 1` to
`(info)->options` avoiding changes in lots of files and adding casts
everywhere.
> -
> struct ip_tunnel_info {
> struct ip_tunnel_key key;
> struct ip_tunnel_encap encap;
> @@ -107,6 +101,7 @@ struct ip_tunnel_info {
> #endif
> u8 options_len;
> u8 mode;
> + u8 options[] __aligned(sizeof(void *))
> __counted_by(options_len);
Since 96 % 16 == 0, I'd check if __aligned_largest would change the
bytecode anyhow... Sometimes it does.
Thanks,
Olek
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