Date: Sun, 22 Jul 2007 20:06:20 -0700 From: John-Mark Gurney <gurney_j@resnet.uoregon.edu> To: Dieter <freebsd@sopwith.solgatos.com> Cc: freebsd-drivers@freebsd.org Subject: Re: userspace driver API ? Message-ID: <20070723030620.GD99491@funkthat.com> In-Reply-To: <200707222308.XAA17276@sopwith.solgatos.com> References: <20070722213451.GA99491@funkthat.com> <200707222308.XAA17276@sopwith.solgatos.com>
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Dieter wrote this message on Sun, Jul 22, 2007 at 16:08 +0100:
> > I've been thinking about similar things for a while... Though I have
> > a few concerns...
> >
> > a) a stable API is something that Linus has touted as something that will
> > not happen for Linux, so yes, it's "stable" but can we truely depend
> > upon that?
>
> >From the bits I read, it sounds like it is the interfaces within
> the kernel that will change at will, the interfaces between the
> kernel and userland will be stable.
>
> > b) w/o direct DMA, it's not as useful, and implementing direct DMA
> > isn't that difficult (I do direct DMA to userland buffers for bktrau
> > and cxd)...
>
> So propose an extension to allow DMA?
>
> Additional concerns include:
>
> Did they get anything significantly wrong?
Can't say, I can't understand the patch... There doesn't appear to
be an interface in the patches that I can make out...
> Did they leave out anything besides DMA?
See above...
> Could this create any security problems?
Most definately... It would allow the userland driver to read and
write to anywhere in physical memory.. That said, it's no more of
a security risk then loading a kernel module and the like...
> It could help the binary-only crowd, since binaries in userland
> aren't quite as bad as binaries in the kernel.
Though to a limited extent... Don't forget there are lots of devices
that consume other interfaces besides providing a cdev to userland...
There's ifnet and geom to name a couple... Exposing cdev only provides
a limited benifit...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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