Re: [PATCH v2 bluetooth-next] Simplify lowpan receive path so skb is freed in lowpan_rcv when dropped.

[Alexander Aring <alex.aring@gmail.com>]

Hi Martin,

On Tue, Sep 09, 2014 at 11:17:15AM +0100, Martin Townsend wrote:
> Hi Alex,
> 
> On 09/09/14 10:46, Alexander Aring wrote:
> > Hi Martin,
> >
> > On Tue, Sep 09, 2014 at 10:28:36AM +0100, Martin Townsend wrote:
> > ...
> >>> I thought more about that, you mean the receiving part only? So the
> >>> uncompression. The point is that we don't have no interface for an user
> >>> that can decide if he like to use UDP compression like RFC 6282 or UDP
> >>> compression like GHC. This is only relevant for the transmit part. So
> >>> compression is optionally. (We should have some interface to make this
> >>> configurable by user -> adding this to the nhc layer, later).
> >> I've implemented compression and decompression. You are right in that we need a mechanism of configuring what gets compressed by what method.
> > ok. But how we deal with that currently with GHC UDP and UDP RFC6282
> > compression. We can't not support both compression methods. 
> >
> > btw. how we should call it now? Uncompression or decompression, I can
> > also name the callbacks to decompression. I am not a native speaker so
> > I will ask you which is better now. :-)
> As an English speaker I have to admit I don't know.  Here's one link I found on the subject
> http://english.stackexchange.com/questions/56480/difference-between-uncompress-and-decompress
> to confuse you even more :)
> 
> >
> >>> On the uncompression part, means the receiving part we can support both.
> >>> UDP RFC 6282 or UDP like GHC, the next header id value should be
> >>> different there. That means currently we can receive every packets but
> >>> transmit only RFC6282 compression formats.
> >>>
> >>> So for receiving this, it's okay. But for compression, since we don't
> >>> have some interface to make this configurable we should use RFC 6282.
> >> So I will ensure UDP is compressed by 6282.  Then I was going to start out by just compressing ICMPv6 with GHC and monitor how much data is saved by using GHC.  Later on we will implement a mechanism of configuring what gets compressed and by which compression method.
> > Okay, you mean that you will leave UDP compression by 6282 but insert a
> > receive handling (decompression) for UDP GHC?
> >
> > RFC6282 doesn't describe any compression/decompression(or uncompression)
> > format for ICMPv6, so we could handle there compression and
> > uncompression. I understand now you did it that way, or?
> For the moment I will assume all ICMPv6 traffic is compressed and decompressed with GHC as this will be the only Next Header Compression format.  In future we need something better.  We also need a method of knowing what compression formats a device supports.  I can see a list of compression formats which could also be a list by protocol.  Then when sending to a device you would select the highest ranking supported compression format for that device.

Is "what compression methods like a device to use" part of any RFC? Is there
something which I don't know? I mean, okay you can do that in any
application layer in userspace. But I don't see that we need something
like this in kernelspace. I know there is no suggestion that you want to
implement something like this in kernelspace, but I want to clarify this.

Application layer in userspace means, use some own coap(or whatever) based
protocol and setup the right compressions via userspace by some application.

- Alex