linux-kernel - Re: [PATCH] crypto: compress

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Date:	Thu, 19 Feb 2009 10:12:18 +0100 (CET)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
cc:	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: compress - Add pcomp interface

On Thu, 19 Feb 2009, Herbert Xu wrote:
> On Thu, Feb 12, 2009 at 04:19:40PM +0100, Geert Uytterhoeven wrote:
> > On Tue, 10 Feb 2009, Herbert Xu wrote:
> > > On Thu, Feb 05, 2009 at 05:24:51PM +0100, Geert Uytterhoeven wrote:
> > > > > Well with the netlink parameters these can have variable lengths
> > > > > depending on how many parameters the user supplies.
> > > > 
> > > > How can this be exported to userspace?
> > > > How does this variable length parameter passing work? Do you have an example?
> > > 
> > > See how we use it for rtnetlink, e.g., in net/ipv4/ip_gre.c.
> > > 
> > > > Nothing in crypto/ seems to already use nla_*?
> > > 
> > > Well we don't have a user-space API yet :) But checkout the
> > > discussions on this list.
> > 
> > I'm sorry, but this is a totally separate change, so I'm not going to do it
> > right now.
> 
> Sorry but I disagree.  We're working on the user-space API right
> now and having to redo the compression parameters API later because
> we didn't take take user-space into account is just not acceptable.

OK, I'll give it a try...

> In any case, the nla stuff is not as hard is it looks.  It's
> going to add tens of lines to the setup code and that's it.
> 
> In order to get started, all you need to do is call nla_parse.
> You don't even need a policy for the simple attributes.
> 
> Please let me know if you need more help in getting nla_parse
> going.

IIUC, my setup() routines should decode the parameters using nla_parse()?
And the caller of a setup() routine should encode the data. But how? All the
nla_put*() routines seem to be targeted at skb's.

The only place where nla_parse() is called with a void */length pair is
net/sched/em_meta.c:em_meta_change(). But I can find no place where the actual
TCA_EM_META_* fields are encoded.

Can you please explain? Thanks!

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
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