Calling m_pullup in ether_input

[Julian Elischer]

Giorgos Keramidas wrote:

>On 2004-10-09 00:34, Gleb Smirnoff <glebius at freebsd.org> wrote:
>  
>
>>On Fri, Oct 08, 2004 at 06:15:15PM +0300, Giorgos Keramidas wrote:
>>G> In ether_input() we unconditionaly discard the mbufs whose m_len is less than
>>G> ETHER_HDR_LEN.  A bit higher M_PKTHDR has been checked but the check made
>>G> before discarding the frame doesn't pay attention to the m->m_pkthdr.len (the
>>G> total packet length).
>>
>>In my humble opinion, all Ethernet device drivers are intentionally written
>>in such a way that they always pass an mbuf with contigous Ethernet header
>>to ether_input().
>>

I'm not convinced this is true for jumbo backets.

>>    
>>
>
>I know, but thanks for verifying what I had understood so far :-)
>
>  
>
>>Why did you write this patch? Do you really have packet loss?
>>    
>>
>
>Not really.  Just trying to see if there _was_ any packet loss first.
>After running for several hours, the counters are still zero.  I think
>this means the case of dropped packets would be so rare that there's no
>real reason to worry too much about lost packets.
>
>  
>
>>G> I am trying to find out how often this happens, by using the attached patch to
>>G> count the number of small frames received in ether_input() and the number of
>>G> failed m_pullup() attempts that result from that.
>>
>>And what results do you have?
>>    
>>
>
>I'll keep this change in my workstation for a week or so.  No signs of
>dropped packets yet, though.
>
>  
>
>>G> Does this change seem reasonable as an instrumentation  of the particular
>>G> problem or am I unknowingly breaking something in the way ether_input() is
>>G> supposed to work?
>>
>>AFAIK, this patch does not break anything but just adds more processing.
>>    
>>
>
>Thanks for the reply.  I'm (somewhat slowly) learning more about the way
>the networking code.  A little more processing is a small penalty to pay
>for trying out things.
>
>- Giorgos
>
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