netdev - Re: [PATCH 0/2] netem: trace enhancement

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Date:	Wed, 05 Dec 2007 14:05:23 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Ariane Keller <ariane.keller@....ee.ethz.ch>
CC:	Ben Greear <greearb@...delatech.com>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	netdev@...r.kernel.org, herbert@...dor.apana.org.au,
	Rainer Baumann <baumann@....ee.ethz.ch>
Subject: Re: [PATCH 0/2] netem: trace enhancement

Ariane Keller wrote:
> Thanks for your comments!
> 
> Patrick McHardy wrote:
>
>>> But with this we would need the tcm_handle, tcm_parent arguments etc. 
>>> which are not known in q_netem.c
>>> Therefore we would have to change the parse_qopt() function prototype 
>>> in order to pass the whole "req" and not only the nlmsghdr.
>>
>> I assume you mean netem_init, parse_qopt is userspace. But I don't
>> see how that is related, emptying the buffer happens during packet
>> processing, right?
 >
> Actually I meant parse_qopt from user space.
> If we would change that function prototype we would have the whole 
> message header available in netem_parse_opt() and could pass this to the 
> process which is responsible for sending the data to the kernel. This 
> process would use this header every time it has to send new values to 
> the netem_change() function in the kernel module.


You don't actually want to parse tc output in your program?
Just open a netlink socket and do the necessary processing
yourself, libnl makes this really easy.

> I thought about this because I was not aware of the qdisc_notify function.
> Anyway I've got some troubles with calling qdisc_notify.
> 1. I have to do a EXPORT_SYMBOL(qdisc_notify) (currently it is declared 
> static in sch_api.c)

This is fine.

> 2. I'd like to call it from netem_enqueue(), which leads to a "sleeping 
> function called from invalid context", since we are still in interrupt 
> context. Therefore I think I have to put it in a workqueue.

Just change it to use gfp_any().
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