Re: [PATCH bluetooth-next 0/4] 6lowpan: introduce generic 6lowpan private data

Hi Alex,

I already thought many times to introduce something like that. Here is a draft
for introducing the generic 6lowpan private data into each lowpan interface.
For the beginning I introduced the enum "lltype" which contains the LL type of
a lowpan interface.

Use cases for such feature (LL types):

- If we do in upper layers (6LoWPAN/IPv6) a evaluation of dev->type then
  the value is on all lowpan interfaces "APRHRD_6LOWPAN". If we checked on
  "dev->type" and it's ARPHRD_6LOWPAN we can safe use lowpan_priv to get
  6LoWPAN generic private data. With this data we can check the LL type which
  can be currently BTLE or IEEE802154. This could be useful to make different
  handling in iphc compress/decompress and evaluating LL private data of skb
  control block "skb->cb".

  Example (802.15.4 has different address handling functionality):

  switch (lowpan_priv(dev)->lltype) {
  case LOWPAN_LLTYPE_BTLE:
       /* do EUI64 btle handling */
       break;
  case LOWPAN_LLTYPE_IEEE802154:
       /* do complicated short/extended address handling */
       /* we can surely call skb->cb to some other private data from LL
          which was set before iphc compress/decompress function call */
       break;
  }

  The handling is currently for 802.15.4 is in generic 6lowpan code currently
  not quite. This should be handled by private data. At the moment btle use
  the same handling like for 802.15.4 extended address. Nevertheless is we can
  cleanup some handling then in generic iphc functionality.

  This also possible in layers like IPv6, just doing a check on APRHRD_6LOWPAN
  before calling lowpan_priv(dev)->lltype, then we are sure that the private
  data of the interface is a 6LoWPAN interface and we can cast it to lowpan_priv.
  Then we can do 6LoWPAN generic stuff OR 6lowpan specific LL stuff.

- In Lukasz Duda RFC for introducing stateful address compression, I saw
  some behaviour which such functionality is also useful. Currently we don't
  have a allocated space for a 6LoWPAN generic space which is assigned to a
  lowpan interface. When LL layers (BTLE, IEEE802154) calls iphc
  compress/decompress Lukasz had no change to access some room which is needed
  for storing the context information into a table. The workaround for this
  feature was to add allocate a static data room for the table and doing a
  lookup/match of netdev name. Which a generic 6lowpan private data room per each
  lowpan interface we can put this table according to the netdev private room,
  which means in short: no lookup is needed anymore, just dereferencing lowpan_priv.

  In upper layer like IPv6 Lukasz could use that to get the stateful context
  table information as an example for doing 6LoWPAN generic stuff in upper
  layers.


Note about the implementation for LL 6LoWPAN private pointer:

I stole some mechanism from wireless for that. See [0], the vif struct is part
of sdata which is also part of private data of a wireless interface (mac80211).
I hope I can just adapt this behaviour.

- Alex

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org

[0] http://lxr.free-electrons.com/source/include/net/mac80211.h#L1366

changes since PATCH (was RFC before):
- rename ll_type,ll_foo to lltype, llfoo
- add documentation for generic 6lowpan interfaces API
- add net/6lowpan/core.c for core functionality, like setup or cleanup
  lowpan netdev interfaces, which is necessary e.g. heap allocation/free
- add LOWPAN_PRIV_SIZE for provide API functionality to calculate
  private data
- rebase to current bluetooth-next/master
- add documentation in cc for the Documentation branch

changes since v2:
- rename L2/l2 to LL/ll. I think the usually word in ietf for L2 is
  LL which means "link layer". Also ipv6 stack use ll for variables like
  lladdr -> link layer address.
- rebase to current bluetooth-next/master
- remove some brackets in function lowpan_priv.

Alexander Aring (4):
 Bluetooth: 6lowpan: change netdev_priv to lowpan_dev
 6lowpan: add generic 6lowpan netdev private data
 6lowpan: move module_init into core functionality
 documentation: networking: add 6lowpan documentation

Documentation/networking/6lowpan.txt | 51 ++++++++++++++++++++++++++++++++++++
MAINTAINERS                          |  1 +
include/net/6lowpan.h                | 23 ++++++++++++++++
net/6lowpan/Makefile                 |  2 +-
net/6lowpan/core.c                   | 40 ++++++++++++++++++++++++++++
net/6lowpan/iphc.c                   | 19 --------------
net/bluetooth/6lowpan.c              | 11 +++++---
net/ieee802154/6lowpan/6lowpan_i.h   |  3 ++-
net/ieee802154/6lowpan/core.c        |  4 ++-
9 files changed, 128 insertions(+), 26 deletions(-)
create mode 100644 Documentation/networking/6lowpan.txt
create mode 100644 net/6lowpan/core.c

I went ahead and applied all 4 patches to bluetooth-next tree. That way they get exposure.

Regards

Marcel