Date: Mon, 13 Sep 2004 19:13:29 +0200 From: Jeremie Le Hen <jeremie.le-hen@epita.fr> To: Nikita Danilov <nikita@clusterfs.com> Cc: Morten Liebach <m@mongers.org> Subject: Re: FreeBSD on Xserve? Message-ID: <20040913171329.GA16110@garak.epita.fr> Resent-Message-ID: <200409131713.i8DHDkC18493@epita.fr> In-Reply-To: <16708.47393.249768.90818@thebsh.namesys.com> References: <20040912183437.GF20097@mongers.org> <E1C6aQi-000KyU-00.shmukler-mail-ru@f26.mail.ru> <16708.47393.249768.90818@thebsh.namesys.com>
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> UML (User Mode Linux, user-mode-linux.sf.net) is a port of Linux kernel
> to Linux used as an underlying platform. UML kernel is built as a normal
> user-level executable, that is run on a "host" machine, providing
> "guest" Linux instance. You can log into guest, run processes there,
> attach debugger to it, etc. It's more like vmware than jail.
I would add that the UML patch applied to the hosted kernel source deeply
modifies the ptrace(2) infrastructure. All UML processes are in fact
processes on the host kernel, but the UML kernel ptrace's so that it reroutes
all invoked syscalls to itself and mmap's processes address space to its
own one.
There is obviously a major drawback here, since every process may corrupt
the address space of other ones, and even the kernel one. This is the
reason why the SKAS kernel patch was created : this patch modifies the
host kernel so that the MMU can be used to protect addresss spaces, as
if processes were on a real kernel ; of course the UML kernel is then
also protected. I don't know the internal of this patch, my VM skills
are not good enough.
> UML is a part of 2.6 mainline.
This is correct, but usually patches provided on UML website are newer than
those included in the 2.6 source.
Sorry for my english, I'm doing my best to improve it :-).
--
Jeremie LE HEN aka TtZ jeremie.le-hen@epita.fr
ttz@epita.fr
Hi! I'm a .signature virus! Copy me into your ~/.signature to help me spread!
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