On Thu, Jan 28, 2021 at 11:47 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > Noob question - could you point at or provide a quick guide to layering > here? I take there is only one netdev, and something maintains an > internal queue which is not stopped when HW driver stops the qdisc? Yes, there is only one netdev. The LAPB module (net/lapb/) (which is used as a library by the netdev driver - hdlc_x25.c) is maintaining an internal queue which is not stopped when the HW driver stops the qdisc. The queue is "write_queue" in "struct lapb_cb" in "include/net/lapb.h". The code that takes skbs out of the queue and feeds them to lower layers for transmission is at the "lapb_kick" function in "net/lapb/lapb_out.c". The layering is like this: Upper layer (Layer 3) (net/x25/ or net/packet/) ^ | L3 packets (with control info) v The netdev driver (hdlc_x25.c) ^ | L3 packets v The LAPB Module (net/lapb/) ^ | LAPB (L2) frames v The netdev driver (hdlc_x25.c) ^ | LAPB (L2) frames | (also called HDLC frames in the context of the HDLC subsystem) v HDLC core (hdlc.c) ^ | HDLC frames v HDLC Hardware Driver > Sounds like we're optimizing to prevent drops, and this was not > reported from production, rather thru code inspection. Ergo I think > net-next will be more appropriate here, unless Martin disagrees. Yes, I have no problem in targeting net-next instead. Thanks!
