netlink question

netlink question

[Balazs Scheidler]

Hi,

As I need to communicate between two parts of the kernel (a core TCP part,
and a loaded module), Andi suggested to use netlink for this purpose.

Since I'm not too familiar with Netlink (and I saw only userspace-kernel
communication using netlink), I'd need some introductory material about
netlink. Is some information about the subject available? Sample code would
be sufficient as well.

I've tried google but didn't find too much until now, so some help would be
appreciated.

TIA,

-- 
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Re: netlink question

[jamal]

On Wed, 10 Apr 2002, Balazs Scheidler wrote:

> Hi,
>
> As I need to communicate between two parts of the kernel (a core TCP part,
> and a loaded module), Andi suggested to use netlink for this purpose.
>
> Since I'm not too familiar with Netlink (and I saw only userspace-kernel
> communication using netlink), I'd need some introductory material about
> netlink. Is some information about the subject available? Sample code would
> be sufficient as well.
>

Look at notifier_chain_un/register(),un/register_netdevice_notifier(),
and their usage. You could also look at the usage of netdev_state_change()

cheers,
jamal

netlink question

[Giacomo]

Dear netfilter list.

I would like to ask you about a strange issue.

I wrote a software that communicates with kernel space via the netlink socket.

A data structure of 212 byte (+16 byte of netlink header) used to
travel from user to kernel space and viceversa
without any problem.
Inside kernel space, socket buffer is allocated with alloc_skb
together with GFP_ATOMIC flag.

Since a couple of fields in the structure have changed

from __u32 source_ip  to __u32 source_ip[50];

and equivalently __u32 dest_ip became  __u32 dest_ip[50];

__u16 sport;   ->  __u16 sport[50];

__u16 dport;   ->  __u16 dport[50];

kernel began to crash, reporting, among other messages "scheduling
while atomic".

The data structure is now grown up to 788bytes (+16 netlink header).

I introduced in the functions responsible of netlink communication
some printks reporting the value of
in_atomic();

while with little data structures I always read in_atomic() == 0,  in
the same actions, but with the bigger
data structure, sometimes i read in_atomic() == 1


Is there a possible reason for this behaviour?

If yes, how should the behaviour be corrected?

Thanks in advance.

Giacomo, Italy.





-- 
Giacomo S.
http://www.giacomos.it

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Netlink Question

[C. McPherson]

I have some private WiFi ioctl's that are associated with a couple of 
drivers and I would like to convert those private ioctl's into netlink. 
Does anyone know if there is any documentation on this or a URL that I 
could reference before I attempt?

Thanks in advance
Clyde

Re: Netlink Question

[Arend van Spriel]

+ linux-wireless

Not really a backports question so adding linux-wireless

On 08/11/2014 09:21 PM, C. McPherson wrote:
> I have some private WiFi ioctl's that are associated with a couple of
> drivers and I would like to convert those private ioctl's into netlink.
> Does anyone know if there is any documentation on this or a URL that I
> could reference before I attempt?

I guess the "private WiFi ioctl's" you are referring to are the ones 
used in Android wpa_supplicant driver_cmd lib? There is no real cookbook 
on how to add nl80211 commands (maybe I am wrong here), but there are 
sufficient patches to be found in the linux-wireless archive. A recent 
one about key management offload adds a couple of commands and 
attributes which may give an idea what is needed:

http://mid.gmane.org/1406076875-8549-1-git-send-email-clanctot@qca.qualcomm.com

Obviously, you need to modify the "couple of drivers" to deal with the 
nl80211 netlink commands.

Regards,
Arend

> Thanks in advance
> Clyde
>
> --
> To unsubscribe from this list: send the line "unsubscribe backports" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Netlink Question

[Krishna Chaitanya]

On Tue, Aug 12, 2014 at 2:12 PM, Arend van Spriel <arend@broadcom.com> wrote:
>
> + linux-wireless
>
> Not really a backports question so adding linux-wireless
>
> On 08/11/2014 09:21 PM, C. McPherson wrote:
>>
>> I have some private WiFi ioctl's that are associated with a couple of
>> drivers and I would like to convert those private ioctl's into netlink.
>> Does anyone know if there is any documentation on this or a URL that I
>> could reference before I attempt?
>
>
> I guess the "private WiFi ioctl's" you are referring to are the ones used in Android wpa_supplicant driver_cmd lib? There is no real cookbook on how to add nl80211 commands (maybe I am wrong here), but there are sufficient patches to be found in the linux-wireless archive. A recent one about key management offload adds a couple of commands and attributes which may give an idea what is needed:
>
> http://mid.gmane.org/1406076875-8549-1-git-send-email-clanctot@qca.qualcomm.com
>
> Obviously, you need to modify the "couple of drivers" to deal with the nl80211 netlink commands.
>
We had same requirement in our driver,  we have patched the iw to send
custom commands specific to our hardware and used NL80211_CMD_TESTMODE
to process and send it to driver.

Re: Netlink Question

[C. McPherson]

On 08/12/2014 05:32 AM, Krishna Chaitanya wrote:
> On Tue, Aug 12, 2014 at 2:12 PM, Arend van Spriel <arend@broadcom.com> wrote:
>> + linux-wireless
>>
>> Not really a backports question so adding linux-wireless
>>
>> On 08/11/2014 09:21 PM, C. McPherson wrote:
>>> I have some private WiFi ioctl's that are associated with a couple of
>>> drivers and I would like to convert those private ioctl's into netlink.
>>> Does anyone know if there is any documentation on this or a URL that I
>>> could reference before I attempt?
>>
>> I guess the "private WiFi ioctl's" you are referring to are the ones used in Android wpa_supplicant driver_cmd lib? There is no real cookbook on how to add nl80211 commands (maybe I am wrong here), but there are sufficient patches to be found in the linux-wireless archive. A recent one about key management offload adds a couple of commands and attributes which may give an idea what is needed:
>>
>> http://mid.gmane.org/1406076875-8549-1-git-send-email-clanctot@qca.qualcomm.com
>>
>> Obviously, you need to modify the "couple of drivers" to deal with the nl80211 netlink commands.
>>
> We had same requirement in our driver,  we have patched the iw to send
> custom commands specific to our hardware and used NL80211_CMD_TESTMODE
> to process and send it to driver.
> --
> To unsubscribe from this list: send the line "unsubscribe backports" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
Yeah thanks a lot, I could use NL80211_CMD_TESTMODE, I'll have to check 
that out. I was also thinking about using NL80211_CMD_VENDOR. These 
IOCTL's are not and will not be used by wpa_supplicant (but I will check 
out the URL you sent), they are just some custom commands we use with 
several chipsets.

-Clyde

Re: Netlink Question

[Arend van Spriel]

On 08/13/2014 09:01 PM, C. McPherson wrote:
>
> On 08/12/2014 05:32 AM, Krishna Chaitanya wrote:
>> On Tue, Aug 12, 2014 at 2:12 PM, Arend van Spriel <arend@broadcom.com>
>> wrote:
>>> + linux-wireless
>>>
>>> Not really a backports question so adding linux-wireless
>>>
>>> On 08/11/2014 09:21 PM, C. McPherson wrote:
>>>> I have some private WiFi ioctl's that are associated with a couple of
>>>> drivers and I would like to convert those private ioctl's into netlink.
>>>> Does anyone know if there is any documentation on this or a URL that I
>>>> could reference before I attempt?
>>>
>>> I guess the "private WiFi ioctl's" you are referring to are the ones
>>> used in Android wpa_supplicant driver_cmd lib? There is no real
>>> cookbook on how to add nl80211 commands (maybe I am wrong here), but
>>> there are sufficient patches to be found in the linux-wireless
>>> archive. A recent one about key management offload adds a couple of
>>> commands and attributes which may give an idea what is needed:
>>>
>>> http://mid.gmane.org/1406076875-8549-1-git-send-email-clanctot@qca.qualcomm.com
>>>
>>>
>>> Obviously, you need to modify the "couple of drivers" to deal with
>>> the nl80211 netlink commands.
>>>
>> We had same requirement in our driver,  we have patched the iw to send
>> custom commands specific to our hardware and used NL80211_CMD_TESTMODE
>> to process and send it to driver.
>> --
>> To unsubscribe from this list: send the line "unsubscribe backports" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> Yeah thanks a lot, I could use NL80211_CMD_TESTMODE, I'll have to check
> that out. I was also thinking about using NL80211_CMD_VENDOR. These
> IOCTL's are not and will not be used by wpa_supplicant (but I will check
> out the URL you sent), they are just some custom commands we use with
> several chipsets.

If you are using recent kernel or backports package, I would say go for 
the vendor command. It is quite similar to TESTMODE except that it is 
always enabled, ie. not depending on kernel config.

However, if the custom commands would add functionality that might be 
interesting to linux-wireless drivers in general you may consider adding 
them as nl80211 commands.

Regards,
Arend