netdev - Re: [PATCH] Add JMEMCMP to Berkeley Packet Filters

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Date:	Fri, 11 Feb 2011 02:02:11 +0000
From:	Ian Molton <ian.molton@...labora.co.uk>
To:	Octavian Purdila <tavi.purdila@...il.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	rdunlap@...otime.net, isdn@...ux-pingi.de, paulus@...ba.org,
	arnd@...db.de, davem@...emloft.net, herbert@...dor.apana.org.au,
	ebiederm@...ssion.com, alban.crequy@...labora.co.uk,
	astanciu@...acom.com
Subject: Re: [PATCH] Add JMEMCMP to Berkeley Packet Filters

On 10/02/11 15:27, Octavian Purdila wrote:
> On Thu, Feb 10, 2011 at 3:35 PM, Ian Molton<ian.molton@...labora.co.uk>  wrote:
>> On 10/02/11 13:24, Eric Dumazet wrote:
>>
>> Hi!
>>
>> Thanks for reviewing! :)
>>
>>>> * Can sk_run_filter() be called in a context where kmalloc(GFP_KERNEL) is
>>>>    not allowed (I think not)
>>>
>>> You cannot use GFP_KERNEL in sk_run_filter() : We run in {soft}irq mode,
>>> in input path.
>>
>> Ok, that can be sorted.
>>
>>>> * Data section allocated with second call to sock_kmalloc().
>>>> * Should the patch be broken into two - one to add the data uploading,
>>>>    one to add the JMEMCMP insn. ?
>>>
>>> May I ask why it is needed at all ?
>>
>> So we can match strings in packet filters... I don't think I understand the
>> question...
>>
>
> Adding a data section (some sort of persistent memory storage that the
> filter can access) is also useful for creating capture triggers, e.g.
> starting capturing after a marker packet has arrived.

Nice to see that people are thinking of more use-cases.

Eric, I think I understand what you meant now...

Our use case is experimental for now, so I wanted to see if other people 
would find this useful, as adding an experimental feature that is never 
used seems pointless.

In our case, we need to match strings in d-bus packets. if the packet is 
not intended for the recipient, it gets dropped, thus avoiding a 
pointless context switch.

-Ian
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