Serge Hallyn <serge.hal...@canonical.com> writes:
> Quoting Michael H. Warfield (m...@wittsend.com):
>> On Wed, 2013-01-16 at 16:46 -0600, Serge Hallyn wrote:
>> > Quoting Michael H. Warfield (m...@wittsend.com):
>> > > Serge,
>> > >
>> > > Revisiting an earlier remark...
>> > ...
>> > > > Now I tested, and with a simple setup we can use a much simpler
>> > > > patch which just does mount("", "/", NULL, MS_SLAVE|MS_REC, 0);
>> > > > for the whole of chroot_into_slave() (and skips the new umount2()
>> > > > in start.c). The container then starts, and its mounts table
>> > > > is clean.
>> > >
>> > > Were you still looking at this? Currently, with the MS_SHARED patch
>> >
>> > No, I haven't been.
>> >
>> > > work in 0.9.0, the mount table is pretty ugly and running "df" in a
>> > > container is really ugly...
>> > >
>> >
>> > ...
>> >
>> > > > Where that won't work is in a livecd or any fancy raid setup,
>> > > > where your process's / has a parent which is MS_SHARED.
>> > >
>> > > How bad is this breakage in regards to that then?
>>
>> > pivot_root would simply fail.
>>
>> > Likewise, the case where / is actually type 'rootfs', which is
>> > not MS_USER and therefore can't be pivot_root()d from would
>> > fail.
>>
>> > There is something else we could try. Before we chroot() into
>> > our custom MS_SLAVE /, we could fork a child. That child sticks
>> > around, waits for a signal saying the pivot_root+umounts are
>> > done, then it looks through /proc/self/mounts and unmounts
>> > anything which is not under '/root/'.
>>
>> > I think that might really work best.
>>
>> That certainly sounds like it might be worth a shot. If you could get
>> me a patch, I could test. Beginning in a week I'm going to be out of
>> pocket for a couple of weeks with access severely limited to my test
>> servers, though.
>
> Let's remember this for when you get back then - I won't have time (that
> is, be able to justify moving other things) before then.
>
> If someone else wants to write the patch, I think it'll be a fun one to
> write.
No patch. But the way I can report how I solved this in iproute.
mount("", "/", "none", MS_SLAVE | MS_REC, NULL);
Which is the equivalent of "mount --make-rslave /". Which terms off
mount propogation back to the parent user namespace.
I don't know how much it will help but this looks a lot simpler than
what you were doing.
Eric
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