linux-kernel - Re: [PATCH] Driver Core: devtmpfs - kernel-maintained tmpfs-based /dev

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Message-ID: <20090812152623.GB29407@kroah.com>
Date:	Wed, 12 Aug 2009 08:26:23 -0700
From:	Greg KH <greg@...ah.com>
To:	David Dillow <dave@...dillows.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Greg KH <gregkh@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>,
	Jan Blunck <jblunck@...e.de>, Harald Hoyer <harald@...hat.com>,
	Scott James Remnant <scott@...ntu.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] Driver Core: devtmpfs - kernel-maintained tmpfs-based
 /dev

On Wed, Aug 12, 2009 at 10:39:57AM -0400, David Dillow wrote:
> On Wed, 2009-08-12 at 06:44 -0700, Greg KH wrote:
> > On Wed, Aug 12, 2009 at 08:56:53AM -0400, David Dillow wrote:
> > > On Tue, 2009-08-11 at 17:34 -0700, Greg KH wrote:
> > > > On Tue, Aug 11, 2009 at 08:25:27PM -0400, David Dillow wrote:
> > > > > So use Eric/Arjan's program that does it in 60ms -- you get a
> > > > > dynamic /dev, no initrd, fast boot, and no kernel changes required.
> > > > 
> > > > Their program only handles it for a reconstruction of /dev based on
> > > > sysfs one time at boot.  It does not handle things that are added or
> > > > discovered by the system after that, you need udev for that.
> > > > 
> > > > So it's a great hack for boot time stuff, but not a complete /dev
> > > > management replacement like this code can be for numerous systems.
> > > 
> > > What systems would those be?
> > 
> > Rescue disks, Embedded systems with no local users, servers with no
> > local users, etc.  Basically anything that you are only root on, and
> > don't care about group permissions.
> 
> We've discussed those, though, and I think most of those fall under
> either having full control of their static environment, or would have
> something to watch for hotplug events -- udev or a replacement -- and so
> would have the ability to create the node from user space.

Rescue disks and booting to /init/bash have full control over their
static environment?  I don't think so.

> Rescue disks may be an exception, but they only need a minimal
> static /dev and then run a tool to get the initial setup. If you are
> expecting an expert to use them, then either running the tool by hand or
> as a post-modprobe rule should catch updates. They can also run udev (or
> a replacement) with stripped rules if you want to make it friendlier to
> non-expert users.

Ok, so don't use devtmpfs on your rescue disk, let the rest of us have a
choice :)

thanks,

greg k-h
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