[lxc-devel] [PATCH] Support MS_SHARED /

[Michael H. Warfield]

On Wed, 2013-01-16 at 16:46 -0600, Serge Hallyn wrote:
> Quoting Michael H. Warfield (mhw at 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.

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
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