Date:	Thu, 19 Mar 2009 21:46:43 -0700
From:	Greg KH <greg@...ah.com>
To:	Dave Airlie <airlied@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: The Linux Staging tree, what it is and is not.

On Fri, Mar 20, 2009 at 02:26:10PM +1000, Dave Airlie wrote:
> On Thu, Mar 19, 2009 at 4:32 AM, Greg KH <greg@...ah.com> wrote:
> > Hi all,
> >
> > It's been many months since the Linux Kernel developers conference, where the
> > linux-staging tree was discussed and role changed.  It turns out that people
> > are still a bit confused as to what the staging tree is for, and how it works.
> >
> > So here's a short summary, I'm not going into the history or background here,
> > that's a much longer writeup that I'd be glad to do if people are interested.
> >
> >
> > The Linux Staging Tree, what it is and is not.
> >
> > What the Linux Staging tree is:
> >  The Linux Staging tree (or just "staging" from now on) is used to hold
> >  stand-alone[1] drivers and filesystems that are not ready to be merged into
> >  the main portion of the Linux kernel tree at this point in time for various
> >  technical reasons.  It is contained within the main Linux kernel tree so
> >  that users can get access to the drivers much easier than before, and to
> >  provide a common place for the development to happen, resolving the
> >  "hundreds of different download sites" problem that most out-of-tree drivers
> >  have had in the past.
> >
> > What the Linux Staging tree is not:
> >  The staging tree is not a place to dump code and run away, hoping that
> >  someone else will to the cleanup work for you.  While there are developers
> >  available and willing to do this kind of work, you need to get them to agree
> >  to "babysit" the code in order for it to be accepted.
> >
> > Location and Development:
> >  The staging tree is now contained within the main Linux kernel source tree
> >  at the location drivers/staging/.  All development happens within the main
> >  kernel source tree, like any other subsystem within the kernel.  This means:
> >        - the linux-next tree contains the latest version of the staging tree,
> >          with bugfixes that are about to be merged into Linus's tree, as well
> >          as the patches that are to be merged into the next major kernel
> >          release.
> >        - if you wish to do work on the staging tree, checkout the linux-next
> >          tree and send patches based on that.
> >
> > Runtime:
> >  When code from the staging tree is loaded in the kernel, a warning message
> >  will be printed to the kernel log saying:
> >    MODULE_NAME: module is from the staging directory, the quality is unknown, you have been warned.
> >  and the kernel will be tainted with the TAINT_CRAP flag.  This flag shows up
> >  in any kernel oops that might be produced after the driver has been loaded.
> >
> >  Note, most kernel developers have expressed the warning that they will not
> >  work on bugs for when this taint flag has happened, so if you run into a
> >  kernel problem after loading such a module, please work to reproduce the
> >  issue without a staging module loaded in order to be able to get help from
> >  the community.
> >
> > If anyone has any questions that this summary doesn't answer, please let me
> > know.
> 
> What is the target audience for staging?

two different groups:
  - users who want to use their hardware
  - developers working on the code in a common area.

> It doesn't fill the out-of-tree modules void as far as I can tell.

Hm, I think it does.

> The model most users are stuck with are
> a) distro kernel
> b) hw not supported.
> 
> Distro kernel could be any revision from 2.6.15 or something crazy up
> until now.
> 
> Generally you can pull the out of tree modules zip file or repo, build
> it against the kernel you have installed and know works with all your
> other hw and your nvidia binary driver, and the out of tree people
> have wrapped all the API changes so that you don't have to do much in
> theory for it to just build and install on your kernel.

Um, no, I don't think you have looked at these out-of-tree modules much.

> Staging doesn't fulfill this role from my POV:
> a) what sane distro will enable staging drivers? do they care about
> their users?

If the distros look, most of these drivers were already included in
them, I've merged all of the Fedora and Ubuntu and openSUSE out-of-tree
drivers that were previously in their kernels.

So I'm pretty sure they will enable them, just to keep parity with what
they are currently shipping :)

openSUSE enables them for this very reason.

> b) if your distro doesn't enable staging drivers you now have two options:

> 1. distro kernel rebuild with staging drivers enabled if new enough
> distro kernel
> 2. kernel.org kernel build with staging drivers enabled.

That's up to a distro as to what they do.

> For a normal user who just wants his hw to work, these options are
> possibly most unappealing. They still want do just download something
> from out-of-tree which does all the nice API break wrapping for them
> and is 1MB instead of 300MB.

A lot of the work that I've done getting these drivers in to the tree,
is just finding all of the proper patches for the drivers, and getting
the code to build.  A "normal" user wouldn't be able to do that at all.

Take the PSB video driver as an example, just finding the proper patches
took weeks.

thanks,

greg k-h
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