From owner-freebsd-fs@freebsd.org  Thu Aug 24 08:25:07 2017
Return-Path: <owner-freebsd-fs@freebsd.org>
Delivered-To: freebsd-fs@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id A15A0DD96A7
 for <freebsd-fs@mailman.ysv.freebsd.org>; Thu, 24 Aug 2017 08:25:07 +0000 (UTC)
 (envelope-from julian@freebsd.org)
Received: from vps1.elischer.org (vps1.elischer.org [204.109.63.16])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client CN "vps1.elischer.org",
 Issuer "CA Cert Signing Authority" (not verified))
 by mx1.freebsd.org (Postfix) with ESMTPS id 7F0076F29E
 for <freebsd-fs@freebsd.org>; Thu, 24 Aug 2017 08:25:06 +0000 (UTC)
 (envelope-from julian@freebsd.org)
Received: from Julian-MBP3.local (124-148-71-183.dyn.iinet.net.au
 [124.148.71.183]) (authenticated bits=0)
 by vps1.elischer.org (8.15.2/8.15.2) with ESMTPSA id v7O8Ou7k014813
 (version=TLSv1.2 cipher=DHE-RSA-AES128-SHA bits=128 verify=NO);
 Thu, 24 Aug 2017 01:24:59 -0700 (PDT)
 (envelope-from julian@freebsd.org)
Subject: Re: Tips on remote debugging for filesystem code
To: Aijaz Baig <aijazbaig1@gmail.com>, freebsd-fs@freebsd.org
References: <CAHB2L+fx_tbGt7NUf-odG780UgPLqDk34CZo0MNP4VsUTfzeZw@mail.gmail.com>
From: Julian Elischer <julian@freebsd.org>
Message-ID: <046d8df4-71a6-65f5-18ad-50589d6d466d@freebsd.org>
Date: Thu, 24 Aug 2017 16:24:50 +0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0)
 Gecko/20100101 Thunderbird/52.3.0
MIME-Version: 1.0
In-Reply-To: <CAHB2L+fx_tbGt7NUf-odG780UgPLqDk34CZo0MNP4VsUTfzeZw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.23
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs/>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 24 Aug 2017 08:25:07 -0000

On 24/8/17 1:40 pm, Aijaz Baig wrote:
> I am trying to understand the internals of the VFS/VNODE interface in the
> kernel and to that end I was attempting to go through the code flow. Hence
> I hooked up two FreeBSD VMs, one as the server and the second as the client
> using named pipes as serial ports.
>
> I put a breakpoint on say 'ufs_lookup' and I hit it by something as simple
> as doing an 'ls' over a directory. Then I try to step through the code and
> examine how the structures get populated and so on. However when I step
> through the code on (K)GDB after a few lines of C code, the server VM (the
> debugged machine) just kind of freezes while the client (on which GDB is
> run is also waiting on the server) and thereafter I always have to restart
> the server VM
>
> Am I doing something incorrectly? How do you guys normally do it? Keen to
> hear tips and best practices
>
I have had more success recently using BHype to make a Virtual FreeBSD 
machine

and connecting to it using the built-in gdb interface.


Firstly it is easier than a serial interface and secondly you don't 
need two machines.