linux-kernel - Re: linux kernel without file system

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Message-ID: <20090114101828.GA15141@frolo.macqel>
Date:	Wed, 14 Jan 2009 11:18:28 +0100
From:	Philippe De Muyter <phdm@...qel.be>
To:	Xavier Bestel <xavier.bestel@...e.fr>
Cc:	Tomasz Chmielewski <mangoo@...g.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: linux kernel without file system

On Wed, Jan 14, 2009 at 10:52:24AM +0100, Xavier Bestel wrote:
> 
> On Wed, 2009-01-14 at 10:34 +0100, Philippe De Muyter wrote:
> > On Wed, Jan 14, 2009 at 09:46:48AM +0100, Tomasz Chmielewski wrote:
> > >> I need to design a very small embedded system that must only control
> > >> one ethernet port and two serial lines and must fit in a very small flash
> > >> memory.  So I thought about replacing the call to /etc/init by my 
> > >> application
> > >> program and removing all the file-system part of linux.
> > >> Is that doable ?
> > >> Is there a 'standard' way of doing that ?
> > >> The first problem I see is accessing my serial lines.  How could I do that
> > >> without using open("/dev/ttySx"), which requires a file system ?
> > >> Is there a way to access devices that does not require a file-system ?
> > >
> > > You could put everything in initramfs (and embed it in the kernel).
> > 
> > Actually, I was thinking about reducing the footprint of my kernel by
> > removing all the fs-related system calls, so the problem is not where
> > the file-system is, but how to access (serial) devices without giving their
> > "/dev/..." name.
> 
> You can still mount sysfs somewhere and access the device nodes from
> there.

Keeping thinking about it, I now think that my 'application program'
(basically a serial-to-ethernet converter) should be a kernel thread,
because of the small memory constraints.

The question is thus how to access the serial lines from a kernel thread.

Philippe
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