linux-kernel - Re: [PATCH v2] misc: Reserve minor for VFIO

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Message-ID: <20131220023820.GG25322@phenom.dumpdata.com>
Date:	Thu, 19 Dec 2013 21:38:20 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	linux-kernel@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
	arnd@...db.de, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v2] misc: Reserve minor for VFIO

On Wed, Dec 18, 2013 at 02:02:38PM -0800, H. Peter Anvin wrote:
> On 12/18/2013 01:01 PM, Greg KH wrote:
> > On Wed, Dec 18, 2013 at 01:56:32PM -0700, Alex Williamson wrote:
> >> VFIO currently allocates it's own dynamic chardev range, reserving the
> >> first minor for the control part of the interface (/dev/vfio/vfio) and
> >> the remainder for VFIO groups (/dev/vfio/$GROUP).  This works, but it
> >> doesn't support auto loading.  For instance when libvirt checks for
> >> VFIO support it looks for /dev/vfio/vfio, which currently doesn't
> >> exist unless the vfio module is loaded.  By converting the control
> >> device to a misc driver and reserving a static minor, we can enable
> >> auto loading.

Why not have libvirt or systemctl try to load vfio first? If it does
not work it would error out.

Or perhaps make the loading of modules in /dev/vfio automatic? I thought
it was based on the name?

> >>
> >> Reserving the minor is a prerequist to that conversion.  Minor 196
> >> is unused by anything currently in the kernel.
> >>
> >> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> >> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> >> ---
> >>
> >> v2: Plea for ack edition
> >>
> >> As Alan suspected, there's been no response from device@...ana.org,
> >> so there's probably nobody monitoring it anymore.  I've done due
> >> diligence looking at all the callers of misc_register() in linux-next
> >> and cannot find any conflicts with minor 196.  If anyone wants to toss
> >> me an ack or sign-off I'll be happy to bring this in through my vfio
> >> tree, otherwise I'd appreciate if someone wants to take it directly.
> >> Thanks!
> >>
> >>  Documentation/devices.txt  |    1 +
> >>  include/linux/miscdevice.h |    1 +
> >>  2 files changed, 2 insertions(+)
> > 
> > Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > 
> 
> I think Alan Cox was the last person to man <device@...ana.org>... Alan,
> are you still doing that?  (Otherwise patching the file in the Linux
> kernel tree seems eminently sensible... there really isn't any need to
> reserve numbers for out-of-tree drivers anymore.  Just another perk of
> being in-tree.)
> 
> 	-hpa
> 
> 
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