netdev - Re: [PATCH v2 1/3] sctp: Export struct sctp

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Date:	Thu, 4 Aug 2016 11:27:20 +0200
From:	Phil Sutter <phil@....cc>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	David Miller <davem@...emloft.net>,
	Xin Long <lucien.xin@...il.com>,
	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] sctp: Export struct sctp_info to userspace

On Thu, Aug 04, 2016 at 09:13:03AM +0000, David Laight wrote:
> From: Phil Sutter
> > Sent: 03 August 2016 22:23
> > This is required to correctly interpret INET_DIAG_INFO messages exported
> > by sctp_diag module.
> ...
> > diff --git a/include/linux/sctp.h b/include/linux/sctp.h
> > index de1f64318fc4e..fcb4c36461732 100644
> > --- a/include/linux/sctp.h
> > +++ b/include/linux/sctp.h
> > @@ -705,70 +705,6 @@ typedef struct sctp_auth_chunk {
> >  	sctp_authhdr_t auth_hdr;
> >  } __packed sctp_auth_chunk_t;
> > 
> > -struct sctp_info {
> > -	__u32	sctpi_tag;
> ...
> > -	__u32	__reserved3;
> > -};
> > -
> >  struct sctp_infox {
> >  	struct sctp_info *sctpinfo;
> >  	struct sctp_association *asoc;
> > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > index d304f4c9792c4..a406adcc0793e 100644
> > --- a/include/uapi/linux/sctp.h
> > +++ b/include/uapi/linux/sctp.h
> > @@ -944,4 +944,68 @@ struct sctp_default_prinfo {
> >  	__u16 pr_policy;
> >  };
> > 
> > +struct sctp_info {
> > +	__u32	sctpi_tag;
> 
> Should these be uint32_t (etc) for userspace?

Grepping through include/uapi in my clone of net-next, I see 271 results
for uint32_t but 4595 ones for __u32. So while not necessarily correct,
it seems to be the far more popular choice. Do you see any benefit in
using the uint*_t typedefs instead?

> > +	__u32	sctpi_state;
> ...
> > +	__u16	__reserved1;
> 
> Is it worth adding some extra pad here in case anything extra needs
> to be added to this set of data?
> 
> ...
> > +	__u32	__reserved3;
> 
> Think I'd definitely add a few words of pad here.
> Or at least make absolutely sure the interface passes the buffer length and
> allows for kernels that report different length buffers.

I merely copy and pasted the struct from include/linux/sctp.h without
thinking about it's layout. Xin, what are your thoughts about this?

Thanks, Phil