How is the IMQ device positioned in the packet flow of the Linux kernel

Question

I would like to know the exact position of the following device in the packet flow for ingress traffic shaping:

• IFB: Intermediate Functional Block

I would like to better understand how packets are flowing to this device and exactly when this happens to understand what methods for filtering / classification can be used of the following:

• tc filter ... u32 ...
• iptables ... -j MARK --set-mark ...
• iptables ... -j CLASSIFY --set-class ...

It seems hard to find documentation on this topic, any help where to find official documentation would be greatly appreciated as well.

Documentation as far as I know:

• tc: tldp.org HOWTO, lartc.org HOWTO
• imq: IMQ - FAQ, lartc.org
• netfilter packet flow: kernel_flow, docum.org kptd

From the known documentation I interpret the following:

Basic traffic control

figure 1
+-------+                 +------+
|ingress|   +---------+   |egress|
|qdisc  +--->netfilter+--->qdisc |
|eth0   |   +---------+   |eth0  |
+-------+                 +------+

IMQ?

iptables -t mangle -A PREROUTING -i eth0 -j IMQ --todev 0 will result in?

figure 2
+----------+   +-------+   +------+   +----------+
|PREROUTING|   |ingress|   |egress|   |PREROUTING|
|mangle    +--->qdisc  +--->qdisc +--->nat       |
|          |   |imq0   |   |imq0  |   |          |
+----------+   +-------+   +------+   +----------+

and iptables -t mangle -A POSTROUTING -o eth0 -j IMQ --todev 1 will result in?

figure 3
+-----------+   +-------+   +------+   +------+
|POSTROUTING|   |ingress|   |egress|   |egress|
|nat        +--->qdisc  +--->qdisc +--->qdisc |
|           |   |imq1   |   |imq1  |   |eth0  |
+-----------+   +-------+   +------+   +------+