On Tue, Jun 08, 2021 at 12:16:43PM -0500, Eric W. Biederman wrote: > Hannes Reinecke <hare@xxxxxxx> writes: > > > On 6/8/21 4:29 PM, Christian Brauner wrote: > >> On Tue, Jun 08, 2021 at 04:10:08PM +0200, Hannes Reinecke wrote: > >>> On Tue, Jun 08, 2021 Greg-KH wrote: > >>>> On Tue, Jun 08, 2021 at 02:30:50PM +0200, Christian Brauner wrote: > >>>>> On Tue, Jun 08, 2021 at 11:38:16AM +0200, Enrico Weigelt, > >>>>> metux IT consult wrote: > >>>>>> Hello folks, > >>>>>> > >>>>>> > >>>>>> I'm going to implement device namespaces, where containers can get > >>>>>> an entirely different view of the devices in the machine (usually > >>>>>> just a specific subset, but possibly additional virtual devices). > >>>>>> > >>> [ .. ] > >>>>>> Is this a good way to go ? Or what would be a better one ? > >>>>> > >>>>> Ccing Greg. Without adressing specific problems, I should warn you > >>>>> that this idea is not new and the plan is unlikely to go anywhere. > >>>>> Especially not without support from Greg. > >>>> > >>>> Hah, yeah, this is a non-starter. > >>>> > >>>> Enrico, what real problem are you trying to solve by doing this? And > >>>> have you tried anything with this yet? We almost never talk about > >>>> "proposals" without seeing real code as it's pointless to discuss > >>>> things when you haven't even proven that it can work. > >>>> > >>>> So let's see code before even talking about this... > >>>> > >>>> And as Christian points out, you can do this today without any kernel > >>>> changes, so to think you need to modify the kernel means that you > >>>> haven't even tried this at all? > >>>> > >>> Curious, I had been looking into this, too. > >>> And I have to side with Greg and Christian that your proposal should > >>> already be possible today (cf device groups, which curiously has a > >>> near-identical interface to what you proposed). > >>> Also, I think that a generic 'device namespace' is too broad a scope; > >>> some subsystems like net already inherited namespace support, and it > >>> turns out to be not exactly trivial to implement. > >>> > >>> What I'm looking at, though, is to implement 'block' namespaces, to > >>> restrict access to _new_ block devices to any give namespace. > >>> Case in point: if a container creates a ramdisk it's questionable > >>> whether other containers should even see it. iSCSI devices are a similar > >>> case; when starting iSCSI devices from containers their use should be > >>> restricted to that container. > >>> And that's not only the device node in /dev, but would also entail sysfs > >>> access, which from my understanding is not modified with the current code. > >> > >> Hey Hannes. :) > >> > >> It isn't and we likely shouldn't. You'd likely need to get into the > >> business of namespacing devtmpfs one way or the other which Seth Forshee > >> and I once did. But that's really not needed anymore imho. Device > >> management, i.e. creating device nodes should be the job of a container > >> manager. We already do that for example (Hotplugging devices ranging > >> from net devices, to disks, to GPUs.) and it works great. > >> > > Right; clearly you can do that within the container. > > But my main grudge here is not the container but rather the system > > _hosting_ the container. > > That is typically using devtmpfs and hence will see _all_ devices, even > > those belonging to the container. > > This is causing grief to no end if eg the host system starts activating > > LVM on devices which are passed to the qemu instance running within a > > container ... > > > >> To make this really clean you will likely have to significantly rework > >> sysfs too and I don't think that churn is worth it and introduces a > >> layer of complexity I find outright nakable. And ignoring sysfs or > >> hacking around it is also not an option I find tasteful. > >> > > Network namespaces already have the bits and pieces to modify sysfs, so > > we should be able to leverage that for block, too. > > And I think by restricting it to 'block' devices we should be to keep > > the required sysfs modifications in a manageable level. > > > >>> > >>> uevent redirection would help here, but from what I've seen it's only > >>> for net devices; feels a bit awkward to have a network namespace to get > >>> uevents for block devices, but then I'll have to test. > >> > >> Just to move everyone on the same page. This is not specific to network > >> devices actually. > >> > >> You are right though that network devices are correctly namespaced. > >> Specifically you only get uevents in the network namespace that network > >> device is moved into. The sysfs permissions for network devices were > >> correct if you created that network device in the network namespace but > >> they were wrong when you moved a network device between network > >> namespaces (with different owning user namespaces). That lead to all > >> kinds of weird issues. I fixed that a while back. > >> > > Granted, modifying sysfs layout is not something for the faint-hearted, > > and one really has to look closely to ensure you end up with a > > consistent layout afterwards. > > > > But let's see how things go; might well be that it turns out to be too > > complex to consider. Can't tell yet. > > I would suggest aiming for something like devptsfs without the > complication of /dev/ptmx. > > That is a pseudo filesystem that has a control node and virtual block > devices that were created using that control node. Also see android/binder/binderfs.c > > That is the cleanest solution I know and is not strictly limited to use > with containers so it can also gain greater traction. The interaction > with devtmpfs should be simply having devtmpfs create a mount point for > that filesystem. > > This could be a new cleaner api for things like loopback devices. I sent a patchset that implemented this last year.
