[libvirt] Mount events are not propagated to namespaces

[Michal Privoznik]

On 06/16/2017 01:14 PM, Daniel P. Berrange wrote:
> On Fri, Jun 16, 2017 at 10:01:26AM +0200, Michal Privoznik wrote:
>> Dear list,
>>
>> while trying to fix a bug of mine, I've realized the mounts are not
>> being propagated into qemu namespaces once domains are running. That is,
>> imagine you have a domain running and then you plug in a flash disk,
>> mount it into host, because you have a file there that you want to
>> hotplug as a disk to your domain. You're not hotplugging the whole flash
>> disk, but a file on it. Problem is, that the mount event of the flash
>> disk is not propagated to qemu namespace even though the root is
>> remounted as MS_SLAVE|MS_REC right after the namespace is created.
>>
>> After some digging. I am able to reproduce this even without libvirt at all:
>>
>> # mount --make-rshared /
>> # mount | grep floppy
>>   <empty/>
>> # unshare -m /bin/bash
>> # mount --make-rslave /
> 
> The problem here is your 'unshare' command, which mounts '/' as
> private, and it appears the later '--make-rslave' is unable to
> undo this.

Okay.

> 
> If you use
> 
>    unshare -m --propagation slave /bin/sh
> 
> then the example works correctly.

Indeed. And now it also does work for libvirt. I don't know what I have
been doing wrong yesterday.

Thanks!

Michal