netdev - Re: [PATCHv3 net-next 3/4] sctp: add support for generating stream reconf add incoming/outgoing streams request chunk

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Message-ID: <20170120163921.GU3781@localhost.localdomain>
Date:   Fri, 20 Jan 2017 14:39:22 -0200
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     "'Xin Long'" <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>,
        "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        Neil Horman <nhorman@...driver.com>,
        Vlad Yasevich <vyasevich@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCHv3 net-next 3/4] sctp: add support for generating stream
 reconf add incoming/outgoing streams request chunk

On Fri, Jan 20, 2017 at 02:50:01PM +0000, David Laight wrote:
> From: Xin Long
> > Sent: 19 January 2017 17:19
> > This patch is to define Add Incoming/Outgoing Streams Request
> > Parameter described in rfc6525 section 4.5 and 4.6. They can
> > be in one same chunk trunk as rfc6525 section 3.1-7 describes,
> > so make them in one function.
> ...
> > +struct sctp_strreset_addstrm {
> > +	sctp_paramhdr_t param_hdr;
> > +	__u32 request_seq;
> > +	__u16 number_of_streams;
> > +	__u16 reserved;
> > +} __packed;
> ...
> > +		addstrm.param_hdr.type = SCTP_PARAM_RESET_ADD_OUT_STREAMS;
> > +		addstrm.param_hdr.length = htons(size);
> > +		addstrm.number_of_streams = htons(out);
> > +		addstrm.request_seq = htonl(asoc->strreset_outseq);
> > +		addstrm.reserved = 0;
> > +
> > +		sctp_addto_chunk(retval, size, &addstrm);
> 
> Since you allocate the sctp_strreset_addstrm structure on stack
> there is no requirement for it to be packed.

It shouldn't matter that it's allocated on stack. Why should it?
We need it to be packed as this is a header that will be sent out to
another peer, so there can't be any padding on it.

  Marcelo