[Click] Packet alignment

[Sascha Alexander Jopen]

Hey,

i already implemented this solution, it's the easiest one. I hoped for a
more generic solution, which allows to define that my element has an
arbitrary or unknown alignment, another element like UDPIPEncap requires
a specific alignment and click-align would do the rest. Implementing
hardcoded alignements in click-align.cc seems not the best solution,
especially when i use click packages. A more dynamic approach with
elementmap.xml or something like this would be nice, but i guess there
is not enough demand to implement this.

Thanks anyway,
Sascha

Am 31.07.2013 20:05, schrieb Eddie Kohler:
> Another solution is of course to generate the correct amount of
> headroom (say 48B) so that UDPIPEncap is naturally aligned!
> 
> 
> On Wed, Jul 31, 2013 at 2:05 PM, Eddie Kohler <ekohler at gmail.com> wrote:
>> (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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