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SubjectRe: [PATCH 0/3] kobject: support namespace aware udev
On Wed, Sep 09, 2015 at 04:16:49PM -0400, Michael J Coss wrote:
> On 9/9/2015 4:09 PM, Greg KH wrote:
> > On Wed, Sep 09, 2015 at 03:05:29PM -0400, Michael J Coss wrote:
> >> On 9/8/2015 11:54 PM, Greg KH wrote:
> >>> On Tue, Sep 08, 2015 at 10:10:27PM -0400, Michael J. Coss wrote:
> >>>> Currently when a uevent occurs, the event is replicated and sent to every
> >>>> listener on the kernel netlink socket, ignoring network namespaces boundaries,
> >>>> forwarding events to every listener in every network namespace.
> >>>>
> >>>> With the expanded use of containers, it would be useful to be able to
> >>>> regulate this flow of events to specific containers. By restricting
> >>>> the events to only the host network namespace, it allows for a userspace
> >>>> program to provide a system wide policy on which events are routed where.
> >>> Interesting, but why do you need a container to get a uevent at all?
> >>> What uevents do a container care about?
> >>>
> >>> thanks,
> >>>
> >>> greg k-h
> >>>
> >> In our use case, we run a full desktop inside the container, including
> >> X.
> > Ugh, I was worried you were going to say that :(
> >
> >> We run the Xserver in headless mode, and forward a uevent to the
> >> container to allow binding/unbinding of remote keyboard, mice, and
> >> displays. So I want the add/del keyboard events, add/del mouse events,
> >> and add/del display events. This is just one use case, I could image
> >> others. The bottom line is that the current behavior is to broadcast to
> >> everyone all uevents, and I don't see that as correct as it crosses the
> >> network namespace boundaries. It seems to me that you would want to
> >> provide controls as to where you want to forward those uevents, and
> >> that is not a policy that I believe should be in the kernel but rather
> >> in user space.
> > devices are not in namespaces, which is why we don't partition them off
> > at all. And that's why I really don't want to add this type of
> > filtering either. It's up to the "master" container/process/whatever to
> > send uevents to child containers if it really wants to. If we were to
> > ever have devices bound only to namespaces, then it would make sense to
> > only send the uevents for those devices to that namespace.
> >
> > But as that's never going to happen, I don't want to give people a false
> > sense of "separation" here that isn't really there at all.
> >
> > sorry,
> >
> > greg k-h
> >
> Agreed that devices are not in namespaces, but the events are, or at
> least could be.

No, there's no way to tell which event for which device goes to which
namespace, as devices are not in a namespace.

> That master is the host, and to do that I want to
> forward events that the host receives to those individual containers.
> But since the kernel is broadcasting them, I can't have that policy on
> the host, and would have to filter on each container. Or I can do as
> you say and have the master forward events. I don't see this as putting
> the devices into a namespace, but rather managing devices from the
> outside and notifying the container of the event. Just like plugging in
> a monitor to the container.

But you can't "plug a monitor into a container". Nor can you "add a
keyboard to a container". Or a tty device. Or anything else (except
for network devices). Don't try to fake things out as that's not what
is happening here. The kernel shouldn't be allowing things to be sent
only to specific namespaces, as that's a lie, the devices are "global"
and not in a namespace at all.


greg k-h

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