[LARTC] What is drop in Qdisc_ops for?

[LARTC] What is drop in Qdisc_ops for?

[Chris Paulson-Ellis]

Hi,

What is the operation drop() in Qdisc_ops for? What are the requirements on
a new qdisc?

As far as I can tell, the classfull qdiscs just pass it on to child qdiscs
and classless qdiscs drop the most recently queued packet. I can't find any
code that initiates all this though.

The operation is not described in the comments in sch_api.c where enqueue,
dequeue, requeue, reset, init, destroy & change are described (dump isn't
described either).

Chris.

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Re: [LARTC] What is drop in Qdisc_ops for?

[Martin A. Brown]

Chris,

Have you discovered the following source of documentation on the QoS
APIs for linux, yet?

  http://qos.ittc.ukans.edu/howto/index.html

 : What is the operation drop() in Qdisc_ops for?

Well, from the userland perspective, drop is just like a netfilter -j
DROP.  Essentially we are saying "throw that packet away".

 : What are the requirements on a new qdisc?

/me retreats to userland, maybe the link above will provide an answer.

 : As far as I can tell, the classfull qdiscs just pass it on to child
 : qdiscs and classless qdiscs drop the most recently queued packet. I
 : can't find any code that initiates all this though.

Again, try the above documentation.

 : The operation is not described in the comments in sch_api.c where
 : enqueue, dequeue, requeue, reset, init, destroy & change are described
 : (dump isn't described either).

Here's a little bit on dump.

  http://qos.ittc.ukans.edu/howto/node16.html

Good luck,

-Martin

-- 
Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com

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Re: [LARTC] What is drop in Qdisc_ops for?

[Chris Paulson-Ellis]

The description of drop given doesn't make sense. It says that it is
required for qdiscs such as RED which need to drop packets. However, the RED
code drops packets in enqueue (by not queuing them), not by making the
system call the drop op. I can't find any code that calls the drop op,
except for the classfull qdiscs which are just propagating the call to the
child qdiscs.

Chris.

----- Original Message ----- 
From: "Martin A. Brown" <mabrown-lartc@securepipe.com>
To: "Chris Paulson-Ellis" <chris@edesix.com>
Cc: <lartc@mailman.ds9a.nl>
Sent: Thursday, August 07, 2003 1:25 PM
Subject: Re: [LARTC] What is drop in Qdisc_ops for?


>
> Chris,
>
> Have you discovered the following source of documentation on the QoS
> APIs for linux, yet?
>
>   http://qos.ittc.ukans.edu/howto/index.html
>
>  : What is the operation drop() in Qdisc_ops for?
>
> Well, from the userland perspective, drop is just like a netfilter -j
> DROP.  Essentially we are saying "throw that packet away".
>
>  : What are the requirements on a new qdisc?
>
> /me retreats to userland, maybe the link above will provide an answer.
>
>  : As far as I can tell, the classfull qdiscs just pass it on to child
>  : qdiscs and classless qdiscs drop the most recently queued packet. I
>  : can't find any code that initiates all this though.
>
> Again, try the above documentation.
>
>  : The operation is not described in the comments in sch_api.c where
>  : enqueue, dequeue, requeue, reset, init, destroy & change are described
>  : (dump isn't described either).
>
> Here's a little bit on dump.
>
>   http://qos.ittc.ukans.edu/howto/node16.html
>
> Good luck,
>
> -Martin
>
> -- 
> Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com
>
>

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