linux-kernel - Re: [PATCH] iommu: making IOMMU sysfs nodes API public

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Message-ID: <20130222000415.GI21011@truffula.fritz.box>
Date:	Fri, 22 Feb 2013 11:04:15 +1100
From:	David Gibson <david@...son.dropbear.id.au>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	Alexey Kardashevskiy <aik@...abs.ru>,
	Joerg Roedel <joerg.roedel@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu: making IOMMU sysfs nodes API public

On Tue, Feb 19, 2013 at 01:11:51PM -0700, Alex Williamson wrote:
> On Tue, 2013-02-19 at 18:38 +1100, David Gibson wrote:
> > On Mon, Feb 18, 2013 at 10:24:00PM -0700, Alex Williamson wrote:
> > > On Mon, 2013-02-18 at 17:15 +1100, Alexey Kardashevskiy wrote:
[snip]
> > >  Adding the window size to sysfs seems more readily convenient,
> > > but is it so hard for userspace to open the files and call a couple
> > > ioctls to get far enough to call IOMMU_GET_INFO?  I'm unconvinced the
> > > clutter in sysfs more than just a quick fix.  Thanks,
> > 
> > And finally, as Alexey points out, isn't the point here so we know how
> > much rlimit to give qemu?  Using ioctls we'd need a special tool just
> > to check the dma window sizes, which seems a bit hideous.
> 
> Is it more hideous that using iommu groups to report a vfio imposed
> restriction?  Are a couple open files and a handful of ioctls worse than
> code to parse directory entries and the future maintenance of an
> unrestricted grab bag of sysfs entries?

The fact that the memory is locked is a vfio restriction, but the
actual dma window size is, genuinely, a property of the group.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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