Re: [RFC] Extend netlink error codes

[Sam Leffler <sam@xxxxxxxxx>]

On Sep 11, 2004, at 9:24 AM, Thomas Graf wrote:

> * Andi Kleen <20040911155839.GN4431@xxxxxxxxxxxxx> 2004-09-11 17:58
> > IMHO it would be far better to just pass text errors
> > in a variable length packet back.  It's a bit plan9ish,
> > but it would work nicely here and be a bit improvement
> > (especially for the qdiscs)
> I had the same idea and the only good way to do so would
> be to add a char * errbuf or alike to struct netlink_opt
> and access it via skb.sk.sk_protinfo.
>
> The bad side is that the for example cls and sch api don't
> provide the skb to the implementing modules and therefore
> they can't access the error buffer. I don't want to change
> all netlink users because of this.
>
> Changing all paths back to netlink_ack to provide a struct
> containing the errno and an additional text error buffer is
> no option for me either.
>
> Correct me if I'm wrong.
>
> > Otherwise you will end up with a mainteance nightmare of a
> > long list of error codes that needs to be updated for every new
> > subsystem.
> I would suggst to split them up and assign blocks of free codes
> to subsystems.
>
> > And everybody who has a patch to add a new netlink
> > user would always fight with conflicts in this file.
> This is indeed a problem.
>
> > I don't think an very specific error like
> > "CFQ subsystem parameter X is FOO, can be only upto BAR"
> > can be nicely put into a global error file.
> True, I would really like to have such error messages.
A technique used for mbuf packet tags in FreeBSD is to define a 32-bit 
cookie that uniquely identifies a module or ABI code and concatenate 
this with the 16-bit tag number.  The ABI code is defined as the 
date+time that the module is created, expressed as the number of 
seconds since the epoch (e.g. the output of date -u +'%s').  Tag 
numbers are meaningful only within the context of the module/ABI.  A 
default/compatibility cookie is used for compatibility with previously 
defined tag values.  This scheme effectively distributes management of 
tags (so far there have been no collisions).
Check the comments in sys/sys/mbuf.h on FreeBSD for more details.

        Sam