linux-kernel - Re: [PATCH 3/4] scripts/gdb: Add rb tree iterating utilities

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Date:   Tue, 26 Mar 2019 10:05:36 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Kieran Bingham <kbingham@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Douglas Anderson <dianders@...omium.org>,
        Nikolay Borisov <n.borisov.lkml@...il.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Jackie Liu <liuyun01@...inos.cn>
Subject: Re: [PATCH 3/4] scripts/gdb: Add rb tree iterating utilities

Quoting Kieran Bingham (2019-03-26 01:52:10)
> Hi Stephen,
> 
> On 25/03/2019 18:45, Stephen Boyd wrote:
> > Implement gdb functions for rb_first(), rb_last(), rb_next(), and
> > rb_prev(). These can be useful to iterate through the kernel's red-black
> > trees.
> 
> I definitely approve of getting data-structure helpers into scripts/gdb,
> as it will greatly assist debug options but my last attempt to do this
> was with the radix-tree which I had to give up on as the internals were
> changing rapidly and caused continuous breakage to the helpers.

Thanks for the background on radix-tree. I haven't looked at that yet,
but I suppose I'll want to have that too at some point.

> 
> Do you foresee any similar issue here? Or is the corresponding RB code
> in the kernel fairly 'stable'?
> 
> 
> Please could we make sure whomever maintains the RBTree code is aware of
> the python implementation?
> 
> That said, MAINTAINERS doesn't actually seem to list any ownership over
> the rb-tree code, and get_maintainers.pl [0] seems to be pointing at
> Andrew as the probable route in for that code so perhaps that's already
> in place :D

I don't think that the rb tree implementation is going to change. It
feels similar to the list API. I suppose this problem of keeping things
in sync is a more general problem than just data-structures changing.
The only solution I can offer is to have more testing and usage of these
scripts. Unless gdb can "simulate" or run arbitrary code for us then I
think we're stuck reimplementing kernel internal code in gdb scripts so
that we can get debug info out.