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Re: Virtual file systems

From: Marcus Brinkmann
Subject: Re: Virtual file systems
Date: Thu, 4 Sep 2003 09:13:15 +0200
User-agent: Mutt/1.5.4i

On Wed, Sep 03, 2003 at 09:31:47AM -0300, brunoacf wrote:
> There is some effort to implement
> virtual filesystems like procfs and
> devfs into the Hurd? Sometime ago I
> saw a discussion about "Hurd do not
> need procfs" in the mailing lists but
> I still believe it would be a good
> improvement.

If you say procfs, you are probably thinking about the Linux /proc
filesystem.  There is some information accessible via the trusted proc
server, and for other information in the Hurd you can access tasks directly to
get it (see the msgport program, for example - in the L4 port, this includes
even basic stuff like inspecting memory).

This can theoretically also be done by procfs.  But only theoretically.  In
reality, this would mean that the procfs filesystem contacts the process on
your behalf.  But this means that if the process is malicious and does block
indefinitely on the request, the procfs thread would be stuck.  It could use
a timeout, but even a small timeout makes a server vulnerable to denial of
service attacks.

So, there are security issues in the Hurd which make a proc filesystem a
suboptimal solution.  Only some of the features of a Linux proc filesystem
could be provided by such a system wide translator.

So, such a translator could be written, but it would usefully be implemented
as a translator that should be run by the users themselves, and thus
consumes their resources, rather than system wide.

Device fs is different.  Given the pityful state of device drivers in GNU
Mach, this doesn't make much sense today.  With the port to L4, we will have
a much more dynamic framework, and it will make sense and probably be
implemented.  Device fs is different because the device drivers are trusted
and centralized (as opposed to procfs, where the information is distributed
and provided by untrusted sources).


`Rhubarb is no Egyptian god.' GNU
Marcus Brinkmann              The Hurd

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