From: Michael Ellerman <michael@ellerman.id.au>
To: Arnd Bergmann <arnd@arndb.de>
Cc: qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>,
KVM list <kvm@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Eric Northup <digitaleric@google.com>,
Scott Wood <scottwood@freescale.com>, Avi Kivity <avi@redhat.com>
Subject: Re: [Qemu-devel] [RFC] Next gen kvm api
Date: Thu, 16 Feb 2012 12:04:05 +1100 [thread overview]
Message-ID: <1329354245.6976.25.camel@concordia> (raw)
In-Reply-To: <201202152221.36154.arnd@arndb.de>
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On Wed, 2012-02-15 at 22:21 +0000, Arnd Bergmann wrote:
> On Tuesday 07 February 2012, Alexander Graf wrote:
> > On 07.02.2012, at 07:58, Michael Ellerman wrote:
> >
> > > On Mon, 2012-02-06 at 13:46 -0600, Scott Wood wrote:
> > >> You're exposing a large, complex kernel subsystem that does very
> > >> low-level things with the hardware. It's a potential source of exploits
> > >> (from bugs in KVM or in hardware). I can see people wanting to be
> > >> selective with access because of that.
> > >
> > > Exactly.
> > >
> > > In a perfect world I'd agree with Anthony, but in reality I think
> > > sysadmins are quite happy that they can prevent some users from using
> > > KVM.
> > >
> > > You could presumably achieve something similar with capabilities or
> > > whatever, but a node in /dev is much simpler.
> >
> > Well, you could still keep the /dev/kvm node and then have syscalls operate on the fd.
> >
> > But again, I don't see the problem with the ioctl interface. It's nice, extensible and works great for us.
> >
>
> ioctl is good for hardware devices and stuff that you want to enumerate
> and/or control permissions on. For something like KVM that is really a
> core kernel service, a syscall makes much more sense.
Yeah maybe. That distinction is at least in part just historical.
The first problem I see with using a syscall is that you don't need one
syscall for KVM, you need ~90. OK so you wouldn't do that, you'd use a
multiplexed syscall like epoll_ctl() - or probably several
(vm/vcpu/etc).
Secondly you still need a handle/context for those syscalls, and I think
the most sane thing to use for that is an fd.
At that point you've basically reinvented ioctl :)
I also think it is an advantage that you have a node in /dev for
permissions. I know other "core kernel" interfaces don't use a /dev
node, but arguably that is their loss.
> I would certainly never mix the two concepts: If you use a chardev to get
> a file descriptor, use ioctl to do operations on it, and if you use a
> syscall to get the file descriptor then use other syscalls to do operations
> on it.
Sure, we use a syscall to get the fd (open) and then other syscalls to
do operations on it, ioctl and kvm_vcpu_run. ;)
But seriously, I guess that makes sense. Though it's a bit of a pity
because if you want a syscall for any of it, eg. vcpu_run(), then you
have to basically reinvent ioctl for all the other little operations.
cheers
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next prev parent reply other threads:[~2012-02-16 1:04 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-02 16:09 [RFC] Next gen kvm api Avi Kivity
[not found] ` <CAB9FdM9M2DWXBxxyG-ez_5igT61x5b7ptw+fKfgaqMBU_JS5aA@mail.gmail.com>
2012-02-02 22:16 ` [Qemu-devel] " Rob Earhart
2012-02-05 13:14 ` Avi Kivity
2012-02-06 17:41 ` Rob Earhart
2012-02-06 19:11 ` Anthony Liguori
2012-02-07 12:03 ` Avi Kivity
2012-02-07 15:17 ` Anthony Liguori
2012-02-07 16:02 ` Avi Kivity
2012-02-07 16:18 ` Jan Kiszka
2012-02-07 16:21 ` Anthony Liguori
2012-02-07 16:29 ` Jan Kiszka
2012-02-15 13:41 ` Avi Kivity
2012-02-07 16:19 ` Anthony Liguori
2012-02-15 13:47 ` Avi Kivity
2012-02-07 12:01 ` Avi Kivity
2012-02-03 2:09 ` Anthony Liguori
2012-02-04 2:08 ` Takuya Yoshikawa
2012-02-22 13:06 ` Peter Zijlstra
2012-02-05 9:24 ` Avi Kivity
2012-02-07 1:08 ` Alexander Graf
2012-02-07 12:24 ` Avi Kivity
2012-02-07 12:51 ` Alexander Graf
2012-02-07 13:16 ` Avi Kivity
2012-02-07 13:40 ` Alexander Graf
2012-02-07 14:21 ` Avi Kivity
2012-02-07 14:39 ` Alexander Graf
2012-02-15 11:18 ` Avi Kivity
2012-02-15 11:57 ` Alexander Graf
2012-02-15 13:29 ` Avi Kivity
2012-02-15 13:37 ` Alexander Graf
2012-02-15 13:57 ` Avi Kivity
2012-02-15 14:08 ` Alexander Graf
2012-02-16 19:24 ` Avi Kivity
2012-02-16 19:34 ` Alexander Graf
2012-02-16 19:38 ` Avi Kivity
2012-02-16 20:41 ` Scott Wood
2012-02-17 0:23 ` Alexander Graf
2012-02-17 18:27 ` Scott Wood
2012-02-18 9:49 ` Avi Kivity
2012-02-17 0:19 ` Alexander Graf
2012-02-18 10:00 ` Avi Kivity
2012-02-18 10:43 ` Alexander Graf
2012-02-15 19:17 ` Scott Wood
2012-02-12 7:10 ` Takuya Yoshikawa
2012-02-15 13:32 ` Avi Kivity
2012-02-07 15:23 ` Anthony Liguori
2012-02-07 15:28 ` Alexander Graf
2012-02-08 17:20 ` Alan Cox
2012-02-15 13:33 ` Avi Kivity
2012-02-15 22:14 ` Arnd Bergmann
2012-02-10 3:07 ` Jamie Lokier
2012-02-03 18:07 ` Eric Northup
2012-02-03 22:52 ` [Qemu-devel] " Anthony Liguori
2012-02-06 19:46 ` Scott Wood
2012-02-07 6:58 ` Michael Ellerman
2012-02-07 10:04 ` Alexander Graf
2012-02-15 22:21 ` Arnd Bergmann
2012-02-16 1:04 ` Michael Ellerman [this message]
2012-02-16 19:28 ` Avi Kivity
2012-02-17 0:09 ` Michael Ellerman
2012-02-18 10:03 ` Avi Kivity
2012-02-16 10:26 ` Avi Kivity
2012-02-07 12:28 ` Anthony Liguori
2012-02-07 12:40 ` Avi Kivity
2012-02-07 12:51 ` Anthony Liguori
2012-02-07 13:18 ` Avi Kivity
2012-02-07 15:15 ` Anthony Liguori
2012-02-07 18:28 ` Chris Wright
2012-02-08 17:02 ` Scott Wood
2012-02-08 17:12 ` Alan Cox
2012-02-05 9:37 ` Gleb Natapov
2012-02-05 9:44 ` Avi Kivity
2012-02-05 9:51 ` Gleb Natapov
2012-02-05 9:56 ` Avi Kivity
2012-02-05 10:58 ` Gleb Natapov
2012-02-05 13:16 ` Avi Kivity
2012-02-05 16:36 ` [Qemu-devel] " Anthony Liguori
2012-02-06 9:34 ` Avi Kivity
2012-02-06 13:33 ` Anthony Liguori
2012-02-06 13:54 ` Avi Kivity
2012-02-06 14:00 ` Anthony Liguori
2012-02-06 14:08 ` Avi Kivity
2012-02-07 18:12 ` Rusty Russell
2012-02-15 13:39 ` Avi Kivity
2012-02-15 21:59 ` Anthony Liguori
2012-02-16 8:57 ` Gleb Natapov
2012-02-16 14:46 ` Anthony Liguori
2012-02-16 19:34 ` Avi Kivity
2012-02-15 23:08 ` Rusty Russell
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