Date: Fri, 24 Feb 2012 12:56:51 -0800
From: Greg KH <gregkh@linuxfoundation.org>
To: Henrik Rydberg <rydberg@euromail.se>
Cc: Guenter Roeck <guenter.roeck@ericsson.com>,
        Jidong Xiao <jidong.xiao@gmail.com>,
        Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: Can we move device drivers into user-space?
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On Fri, Feb 24, 2012 at 09:37:15PM +0100, Henrik Rydberg wrote:
> On Fri, Feb 24, 2012 at 12:16:55PM -0800, Greg KH wrote:
> > On Fri, Feb 24, 2012 at 09:10:27PM +0100, Henrik Rydberg wrote:
> > > I am not complaining about the kernel and its driver structure - on
> > > the contrary. I do, however, see a reason why constructing lower-level
> > > interfaces to userspace may be of benefit. The kernel is growing
> > > tremendously fast. Sooner or later, parts of the present driver
> > > responsibility will have to be split into smaller chunks. Why not
> > > place those chunks outside the kernel itself?
> > 
> > I fail to understand why you think the growth of the kernel will require
> > drivers to be split into chunks in the future.  Are we somehow growing
> > faster than is required / needed / wanted and outstripping the size of
> > what we are allowed to take up on machines?
> 
> How long can one grow and still claim to _be_ a kernel?

You tell me.  I know of lots of "kernels" that are far bigger than
Linux, and people still consider them a kernel.

> The current
> (arbitrary) split between kernel and userland was made a long time
> ago. For a number of reasons, of course, but not least out of
> convenience. Projecting the current kernel growth ten years into the
> future, will there still not be another (arbitrary) convenient split?

Why?  What problems are we having with our existing user/kernel split
that would drive such a change?

> Even so, the main point was not whether a secondary split may or may
> not happen, but what will happen to the quality of the total system
> when/if that happens. I doubt the fate of userland drivers would be so
> heatedly discussed if everyone believed that work would be carried out
> with the same quality currently found in the kernel.

Quality is not the only reason we don't want userspace drivers for some
types of devices.  Realize what drivers provide to userspace today and
you will understand that.

thanks,

greg k-h
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