+ networking experts
On 08/02/2013 09:49 AM, Mathieu Devos wrote:
Hi,
An update is in order here I believe (and an apology because I
resorted to asking my questions on IRC and not sticking to the mailing
list, for that: sorry).
Let's start things off quickly with my main goal with this: the code
that I'm trying to write is supposed to be an adapter for a new type
of internet (RINA), this is in function of my master thesis (I'm new
to Linux Kernel itself). So what exactly does this mean? I'd like to
be able to hook packets (skb) in the kernel with an LKM and just use
one layer (datalink layer) with the hardware layer being handled by
the drivers and the hardware itself. Everything on top of that should
be RINA specific code.
So basically you want to be able to use RINA stack as a drop-in
replacement for the TCP/IP stack keeping the netdev api unchanged so
device drivers do not have to change.
The specifics about the master thesis is that this all should be done
on android, thus using the wireless stack.
I can not follow your line of thinking here. The android requirement (a
stupid one if you ask me) does not restrict you to the wireless stack.
There are android platforms with ethernet connectivity.
I believed that in an
skbuff you had the formed 802.3 header through drivers but you still
also had the original 802.11 header, this however, is now proven
wrong, the 802.11 header is thrown out after the drivers are done with
it thus it's impossible for me to map RINA to the 802.11 header. After
resuming testing with this news I'm still left with a couple of
questions however:
An sk_buff is just a structure that makes it convenient to add or remove
layer specific header (or tail) data moving from one layer to the other.
An ethernet device with get an 802.3 packet, which is straightforward. A
wireless device also gets an 802.3 packet so from the networking stacks'
perspective there is no difference between a ethernet or a wireless device.
Looking at architecture shown in [1], I think RINA does not need to care
about 802.11 either as the device drivers have their own 802.11 stack,
which takes care of converting 802.3 to 802.11 packets and vice versa
(or use the kernel provided 802.11 stack, ie. mac80211 to take care of
that).
- Can I still use the added functionality of 802.11 as compared to
802.3 by talking directly to the device and setting it's fields? I'm
thinking of using "struct wireless_device" and/or "struct wiphy" and
the functions that come with it.
As said I do not think you should care about 802.11. The structures
mentioned are data structures for configuration purposes on respectively
wireless interface and wireless device level.
- Is it possible to find a general form of skb frame with correctly
set headers? I have currently tested my code
(https://github.com/mathieudevos/kernelmodules/blob/master/ethernet_test.c)
and on one android device (galaxy S2 I9100, BCM4330 wireless chip) I
had my 802.3 header by at my skb->head. On my own htc one X (htc
endeavoru, wireless chip unknown still) I had my 802.3 header at my
skb->mac_header and on my notebook (wireless 5100 AGN) this header was
present on skb->data. Is it coincidence that these 3 are totally
different and is there a function (that perhaps calls the drivers) to
set these skb's in the correct prepared form? And if so, will this
break when I void the layers on top of the mac layer.
How generic do you want it to be? As said the sk_buff is a pretty dumb
struct which is mostly protocol/stack independent. General advice here
is to avoid dealing with the pointers directly and use skb function api.
The hook mechanism dev_add_pack() you are using in [2] is new to me, but
it seems you are doing it while the packet is being processed in the
network stack so the state of the sk_buff can be pretty unpredictable.
Just remember you are probably not the only one handling this packet.
The stack internals are something I tend to stay clear off. Maybe one of
the networking experts can elaborate.
While I know that a part of this still needs to be researched, for
instance say it's possible to set certain fields of the device to use
added 802.11 functionality I won't be setting the channel manually,
that's still left to the driver, but other added functions might be
more useful for RINA.
Examples of useful wireless specific functions? As I see it RINA is an
IPC based network stack on top of some physical layer, ie. ethernet. The
architectural picture in [1] even shows it can run on top of a TCP/IP
stack using sockets.
What I'm hoping to achieve before really heading off into this new
linux adventure is to be able to properly receive an SKB that has the
same format on my devices and later down the road try to send set up
an SKB and send that one myself.
It seems to me that you should familiarize yourself with linux
networking artifacts. Maybe [3] is a good read although it may be pretty
outdated.
Regards,
Arend
[1]
http://irati.eu/irati-first-phase-report-on-use-cases-requirements-analysis-updated-rina-specifications-and-high-level-software-architecture-available/
[2]
https://github.com/mathieudevos/wifi_kernelmodules/blob/master/ethernet_test.c
[3] http://shop.oreilly.com/product/9780596002558.do
On Wed, Jul 31, 2013 at 5:11 PM, Mathieu Devos <mathieu.devos@xxxxxxxx> wrote:
This is my hook: it gets called after I set dev to wlan0. I used a
guide for this and it seems to work for my notebook where I'm able to
find the 802.3 header but still no 802.11.
static int ptype_function(struct sk_buff *skb, struct net_device *dev,
struct packet_type *ptype, struct net_device *dev2);
static void throw_hook(struct net_device *dev){
ptype.type = htons(ETH_P_ALL);
ptype.func = &ptype_function;
ptype.dev = dev;
dev_add_pack(&ptype);
printk(KERN_CRIT "Done setting up packet type");
}
All code can be found here:
android: https://github.com/mathieudevos/kernelmodules/blob/master/ethernet_test.c
notebook: https://github.com/mathieudevos/wifi_kernelmodules/blob/master/ethernet_test.c
Kind regards,
Mathieu Devos
On Wed, Jul 31, 2013 at 5:04 PM, Arend van Spriel <arend@xxxxxxxxxxxx> wrote:
On 07/31/2013 03:45 PM, Mathieu Devos wrote:
Alright,
Seems like I have fixed some issues while added some others. Since I
assume that when my hook gets activated the data pointer should be at
the start of the 802.3 header I casted an ethhdr (8023) on top of that
and it seems that on my notebook this is handled correctly (I can
actually check on my own mac addr and see that these frames are
for/from me).
How does your hook work? Are you intercepting packets?
Regards,
Arend
On Wed, Jul 31, 2013 at 2:55 PM, Arend van Spriel <arend@xxxxxxxxxxxx>
wrote:
On 07/31/2013 02:39 PM, Mathieu Devos wrote:
Hi,
The wireless chip is a Broadcast BCM4330 chip. After looking around a
bit I found that this is a fullMAC and links to the driver on
wireless.kernel: http://wireless.kernel.org/en/users/Drivers/brcm80211
and also links directly to android itself:
https://android.googlesource.com/platform/hardware/broadcom/wlan
I suspected. The bcm4330 is indeed a fullmac device, which means the
802.11
stack is running on the device. The driver on Android is located under:
https://android.googlesource.com/kernel/samsung/+/android-samsung-3.0-ics-mr1/drivers/net/wireless/bcmdhd/
Not sure which android version you have.
The brcm80211 on wireless.kernel.org is the upstream linux driver.
Gr. AvS
Still trying to learn a lot in this tightly packed world of protocol
stacks, wireless and all the other poisons. Seems like I still have a
long way to go. Thank you already for helping me out with these issues
and taking the time to explain these things to me.
Kind regards,
Mathieu Devos
On Wed, Jul 31, 2013 at 1:05 PM, Arend van Spriel <arend@xxxxxxxxxxxx>
wrote:
On 07/31/2013 12:28 PM, Mathieu Devos wrote:
Hi,
It's an android smartphone (I 9100 - Samsung galaxy S2) so it does not
have a normal ethernet 802.3 input even. I check before selecting the
device that it's wireless (through ieee80211_ptr) and this properly
returns the wlan0 device which should be on the 80211 standard.
*sigh* Welcome in the world of protocol stacks, wireless, networking
(choose
your poison). Let me draw the picture.
o user-space
|
----------------------
| kernel
+-----------+
| NET | networking subsystem, ie. TCP/IP stack
+-----------+
| 802.3
+----------------+
| | driver |
| +------------+ |
| |802.11 stack| |
| +------------+ |
| | 802.11 |
+----------------+
|
o RF
The device hooks up to the networking subsystem as an ethernet device
and
as
such it receives 802.3 packets. These are converted to 802.11 packets
by
the
802.11 stack. Now depending on your device that happens in the device
driver
or on the device itself. Another option is that this is done by
mac80211
(kernel provided 802.11 stack), but that is probably not the case, but
to
be
sure I ask again: what wireless device do you have in your galaxy S2?
Gr. AvS
My goal is to get the ieee80211_header properly on the skb with this
device, but some of the pointers and original data in the skb seem
totally off. This leaves me clueless as to where to put this
ieee80211_header.
I've tried putting it right on skb->head (wrong I know, but I was
getting desperate), on skb->mac_header (also wrong, no idea why
though), I went back from skb->tail with len and even added ETH_HLEN
to that as well because you can see that before my hook gets
activated: skb_pull_inline(skb, ETH_HLEN);
In the end I'm left with a header that is forced onto data but with a
wrong origin pointer thus basically leaving me with all wrong data in
the header.
Kind regards,
Mathieu Devos
On Wed, Jul 31, 2013 at 12:08 PM, Arend van Spriel
<arend@xxxxxxxxxxxx>
wrote:
On 07/31/2013 11:39 AM, Mathieu Devos wrote:
Hi,
I hope this is the right place to ask for a little bit of help as
I'm
currently beyond stuck on a challenge I'm trying to accomplish. I'm
trying to write a "simple" LKM that properly uses a ieee80211 header
to print information about the mac addresses (addr1->addr4) and
later
down the road try to send my own data.
I only need to get L2 working, no need for TCP/IP, just a proper
ieee80211 based on input from skb would be huge for me.
So my issue: when placing the ieee80211 on my mac_header after I
hook
my skb from my wireless device (wlan0 on android - I9100)
Not sure what you goal is, but what wireless device is that? You may
just
get 802.3 packets from the device.
Gr. AvS
I get a huge
amount of zero's and random(?) numbers when trying to print the
addresses. This leads me to the first conclusion that mac_header is
placed wrong when using 80211. After that I saw a lot of people just
using the skb->data pointer. Now this gives even weirder issues for
me
and actually totally crashes my kernel.
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