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

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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@xxxxxxx>
> Cc: linux-doc@xxxxxxxxxxxxxxx
> 
> [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

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