Re: [libvirt] PATCH: Allow LXC to use private /dev/pts instance
On Wed, Apr 15, 2009 at 01:55:18PM -0500, Serge E. Hallyn wrote:
...
> Index: src/lxc_container.c
> ===================================================================
...
This all looks good, though I haven't tested it yet.
> + /*
> + * If doing a chroot style setup, we need to prepare
> + * a private /dev/pts for the child now, which they
> + * will later move into position.
> + *
> + * This is complex because 'virsh console' needs to
> + * use /dev/pts from the host OS, and the guest OS
> + * needs to use /dev/pts from the guest.
> + *
> + * This means that we (libvirt_lxc) need to see and
> + * use both /dev/pts instances. We're running in the
> + * host OS context though and don't want to expose
> + * the guest OS /dev/pts there.
> + *
> + * Thus we call unshare(CLONE_NS) so that we can see
> + * the guest's new /dev/pts, without it becoming
> + * visible to the host OS.
> + */
Calling unshare(CLONE_NEWNS) will not prevent the host OS from
seeing the new /dev/pts if / was MS_SHARED. That isn't taken
care of anywhere else for this process's namespace, is it?
Yeah, so this is the place where I think we must still have a difference
in our host setups. I'm testing this patch on a Fedora 11 host, and with
my current code, the new /dev/pts is not visible in the host.
So I can only assume this means my host / is *not* MS_SHARED, while
yours is. I'm struggling to find out why this is different because
I'm testing on an Fedora 11 up2date system.
Anyway, would it be sufficiently to add in a call
if (mount("", "/", NULL, MS_PRIVATE|MS_REC, NULL) < 0) {
virReportSystemError(NULL, errno, "%s",
_("failed to make root private"));
goto cleanup;
}
Just after the 'unshare' call, to make sure our / is private before
we setup the new /dev/pts
I assume the reason you want the new devpts not visible in the
host OS is so that it will be auto-umounted when the container is
released?
Yes, that's the primary reason, although I also just don't want anything
accessing the container's PTYs directly from the host. I wanted them to
remain a hidden impl detail, used only by the libvirt controller process.
So its preferrable that this new dev/pts instance is not visible in the
host (at least not easily).
Daniel
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