[Click] Packet alignment

[Eddie Kohler]

(Not sure but:) Basically, if Click sees an element it doesn't
understand, it assumes the element either doesn't generate packets, or
that it generates packets with correct alignment requirements.

Probably it would be better to default to "arbitrary alignment" rather
than "correct alignment," but that might be difficult.

Eddie


On Wed, Jul 31, 2013 at 12:41 PM, Cliff Frey <clfrey at cisco.com> wrote:
> You need to add your custom element to the "class_factory" function of
> tools/click-align/click-align.cc to indicate the alignment of the packets
> generated by your element.  Then click-align will add the necessary Align
> elements for you.
>
> Cliff
>
>
> On Tue, Jul 30, 2013 at 6:43 AM, Sascha Alexander Jopen <
> jopen at informatik.uni-bonn.de> wrote:
>
>> Hey,
>>
>> I have a question regarding the click packet data alignment.
>>
>> I have an element which generates packets with 46 bytes of headroom
>> followed by some data. The whole packet gets aligned in memory, but
>> data() points to a memory section which is 2 bytes off the alignment on
>> a 32bit machine. This packet will eventually be pushed into an
>> UDPIPEncap element. On some architectures (where
>> HAVE_INDIFFERENT_ALIGNMENT is not defined) a 4-byte alignment is
>> expected (see line 94 udpipencap.cc). However, click-align does not
>> insert an Align element on those architectures. If i do this manually,
>> everything is fine. How can i make click-align insert the Align element?
>>
>> Thanks in advance,
>> Sascha
>>
>> --
>> Dipl.-Inform. Sascha Jopen
>>
>> University of Bonn                     Tel.:   +49-228-73-54219
>> Institute of Computer Science 4        Fax:    +49-228-73-4571
>> Friedrich-Ebert-Allee 144              E-mail: jopen at cs.uni-bonn.de
>> D-53113 Bonn, Germany
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