Subject: Re: [PATCH v2 1/2] sctp: compress bit-wide flags to a bitfield on sctp_sock

From: Joe Perches <[email-masked]>
Date: Wed, 06 Apr 2016 12:53:24 -0700

On Wed, 2016-04-06 at 14:53 -0300, Marcelo Ricardo Leitner wrote:
> It wastes space and gets worse as we add new flags, so convert bit-wide
> flags to a bitfield.
> 
> Currently it already saves 4 bytes in sctp_sock, which are left as holes
> in it for now. The whole struct needs packing, which should be done in
> another patch.
> 
> Note that do_auto_asconf cannot be merged, as explained in the comment
> before it.
> 
> Signed-off-by: Marcelo Ricardo Leitner <[email-masked]>
> ---
[]
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
[]
> @@ -210,14 +210,14 @@ struct sctp_sock {
>  	int user_frag;
>  
>  	__u32 autoclose;
> -	__u8 nodelay;
> -	__u8 disable_fragments;
> -	__u8 v4mapped;
> -	__u8 frag_interleave;
>  	__u32 adaptation_ind;
>  	__u32 pd_point;
> -	__u8 recvrcvinfo;
> -	__u8 recvnxtinfo;
> +	__u16	nodelay:1,
> +		disable_fragments:1,
> +		v4mapped:1,
> +		frag_interleave:1,
> +		recvrcvinfo:1,
> +		recvnxtinfo:1;

Might as well make this __u32 as the next field would be
aligned on an atomic_t

It might be better if these fields didn't use the __ prefix.