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Re: [libvirt] [RFC] [PATCH v3 2/6] add fuse support for libvirt lxc



On Thu, Oct 18, 2012 at 01:25:30PM +0800, Gao feng wrote:
> 于 2012年10月16日 20:23, Daniel P. Berrange 写道:
> > On Mon, Oct 08, 2012 at 08:43:28AM +0800, Gao feng wrote:
> >> 于 2012年09月26日 02:37, Daniel P. Berrange 写道:
> >>> On Tue, Sep 11, 2012 at 10:54:48AM +0800, Gao feng wrote:
> >>>> this patch addes fuse support for libvirt lxc.
> >>>> we can use fuse filesystem to generate sysinfo dynamically,
> >>>> So we can isolate /proc/meminfo,cpuinfo and so on through
> >>>> fuse filesystem.
> >>>>
> >>>> we mount fuse filesystem for every container.the mount name
> >>>> is Lxc-containename-fuse,mount point is
> >>>> localstatedir/run/libvirt/lxc/containername.
> >>>>
> >>>> Signed-off-by: Gao feng <gaofeng cn fujitsu com>
> >>>
> >>>> diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
> >>>> index e5aea11..c5f4951 100644
> >>>> --- a/src/lxc/lxc_controller.c
> >>>> +++ b/src/lxc/lxc_controller.c
> >>>> @@ -1657,6 +1659,14 @@ int main(int argc, char *argv[])
> >>>>          }
> >>>>      }
> >>>>  
> >>>> +    rc = virThreadCreate(&thread, true, lxcRegisterFuse,
> >>>> +                         (void *)ctrl->def);
> >>>> +    if (rc < 0) {
> >>>> +        virReportSystemError(-rc, "%s",
> >>>> +                             _("Create Fuse filesystem failed"));
> >>>> +        goto cleanup;
> >>>> +    }
> >>>> +
> >>>
> >>> This is the wrong place to start FUSE. At this point the LXC
> >>> controller is still sharing its mount namespace with the host
> >>> OS. This causes the FUSE mount for each container to become
> >>> visible in the host, which is not what we want.
> >> sorry for the delay.
> >>
> >> I think it's correct,because host can see container's meminfo
> >> through cgroup too.NOW the container's cgroup can be seen and
> >> modified in container too,I don't know why this is necessary?
> > 
> > The key point is that if you do 'cat /proc/mounts' with your
> > current patch, you see all the LXC container FUSE mounts. These
> > mounts should *not* be visible on the host. Only the libvirt_lxc
> > process and the container itself shoudl see the mounts. This is
> > why you must not start FUSE until after the unshare() call in
> > libvirt_lxc. This also ensures that the FUSE mount is automatically
> > destroyed when libvirt_lxc dies, without you needing to unregister
> > or unmount it.
> > 
> 
> If we start FUSE after the unshare() call in libvirt_lxc,the fuse will
> work in container's environment. and the cgroup is set in the host.
> Can we get host's information in container? I think this is incorrect.

The 'libvirt_lxc' process is not actually running inside the container.
It is running in the host context, but with a slightly customized
filesystem mount namespace, so that it can view /dev from both the
host and container at once.

> I regard the FUSE as a service on host,it provides host's cgroup info
> for the container.

Yes it is a host service, but that is exactly what libvirt_lxc is. All I
am saying is that we must not pollute the host OS' mount table - keep the
mounts hidden in the libvirt_lxc process & container processes only.

Daniel
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