questions about network device drivers

[Abraham vd Merwe <abraham@2d3d.co.za>]

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Hi!

hard_start_xmit() method
========================

when should this function return 0 and when should it return 1 and in which
cases should it do netif_stop_queue() and/or free the dev_kfree_skb() ?

I'd really appreciate it if someone could clear this up. Almost all the
source/docs I've looked at seems to contradict each other ):

also, since hard_start_xmit() is protected by xmit_lock, why are some
drivers (e.g. cs89x0.c) guarding against concurrent calls to
hard_start_xmit (see the spinlock in cs89x0.c:net_send_packet)?

is there any way to control alignment of sk_buff's that gets passed to this
function? e.g. if I want the buffer to be aligned on 16-bit boundary and/or
be padded to a 16-bit boundary - is there any way to tell the kernel to pass
the driver buffers with those characterestics?

get_stats() method
==================

when errors occur that have details error fields in the net_device_stats
structure, am I supposed to increment both the total error count and the
detailed error count or both? also, what about dropped packets?

e.g.

1. i drop a frame because there's no memory left to allocate a sk_buff when
I receive a packet. Do I increment rx_dropped, rx_errors, or both?

2. there's a crc error. do I increment rx_crc_errors and rx_errors or just
rx_crc_errors?

also, I noticed that many drivers keep a private copy of the
net_device_stats structure and just return a pointer to that structure in
the get_stats method. what prevents the other driver methods from racing
with the functions that gets passed this structure?

tx_timeout() method
=================

there is no way to return an error in the tx_timeout method. what should I
do when an error occurs in that function (e.g. I'm unable to reset the
controller)? panic? that seems a bit excessive...

general
=======

What is the difference between netif_wake_queue() and netif_start_queue()?

-- 

Regards
 Abraham

Humor in the Court:
Q.  And who is this person you are speaking of?
A.  My ex-widow said it.

__________________________________________________________
 Abraham vd Merwe - 2d3D, Inc.

 Device Driver Development, Outsourcing, Embedded Systems

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