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

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Message-Id: <20160406.155735.1431363453832315669.davem@davemloft.net>
Date:	Wed, 06 Apr 2016 15:57:35 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	joe@...ches.com
Cc:	marcelo.leitner@...il.com, netdev@...r.kernel.org,
	nhorman@...driver.com, vyasevich@...il.com,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH v2 1/2] sctp: compress bit-wide flags to a bitfield on
 sctp_sock

From: Joe Perches <joe@...ches.com>
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 <marcelo.leitner@...il.com>
>> ---
> []
>> 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.

Indeed, this isn't in a UAPI file so __ prefixed types really aren't
appropriate.