Re: [pve-devel] [PATCH container 1/2] net: Add `link_down` config to allow setting interfaces as disconnected

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Mon, Feb 13, 2023 at 02:56:59PM +0100, Christoph Heiss wrote:
> If this network option is set, the host-side link will be forced down.
> This has the effect that the interface inside the container has
> LOWERLAYERDOWN set, which basically means that the PHY is considered
> down, thus effectivly being "unplugged".
> 
> Also fix some trailing whitespace while touching the file.
> 
> Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
> ---
>  src/PVE/LXC.pm        | 20 +++++++++++++-------
>  src/PVE/LXC/Config.pm |  5 +++++
>  src/lxcnetaddbr       |  3 ++-
>  3 files changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/src/PVE/LXC.pm b/src/PVE/LXC.pm
> index ce6d5a5..039a476 100644
> --- a/src/PVE/LXC.pm
> +++ b/src/PVE/LXC.pm
> @@ -668,7 +668,7 @@ sub update_lxc_config {
> 
>      # some init scripts expect a linux terminal (turnkey).
>      $raw .= "lxc.environment = TERM=linux\n";
> -
> +
>      my $utsname = $conf->{hostname} || "CT$vmid";
>      $raw .= "lxc.uts.name = $utsname\n";
> 
> @@ -932,8 +932,9 @@ sub update_net {
>  	my $oldnet = PVE::LXC::Config->parse_lxc_network($oldnetcfg);
> 
>  	if (safe_string_ne($oldnet->{hwaddr}, $newnet->{hwaddr}) ||
> -	    safe_string_ne($oldnet->{name}, $newnet->{name})) {
> -
> +	    safe_string_ne($oldnet->{name}, $newnet->{name}) ||
> +	    defined($oldnet->{link_down}) != defined($newnet->{link_down})

Doing this here would cause the interface to be deleted and recreated in
a "down" state, which is much more disruptive than it needs to be.
Instead, this should be treated more like we do changing the 'bridge'
property (the 'else' case just below this), and stop after the
`tap_unplug` for the 'down' case.

> +	) {
>  	    PVE::Network::veth_delete($veth);
>  	    delete $conf->{$opt};
>  	    PVE::LXC::Config->write_config($vmid, $conf);
> @@ -1010,6 +1011,11 @@ sub hotplug_net {
>      $cmd = ['lxc-attach', '-n', $vmid, '-s', 'NETWORK', '--', '/sbin/ip', 'link', 'set', $eth ,'up'  ];
>      PVE::Tools::run_command($cmd);
> 
> +    # In case the network device should be disconnected, force the host-link down
> +    if (defined($newnet->{link_down})) {
> +	PVE::Tools::run_command(['/sbin/ip', 'link', 'set', 'dev', $veth, 'down']);

These interfaces are usually part of a bridge, and therefore the next
`ifreload` (and probably some other things) would re-enable them
automatically.

We do need to actually "unplug" them from the bridge (tap_unplug) to
avoid this.

> +    }
> +
>      my $done = { type => 'veth' };
>      foreach (qw(bridge tag firewall hwaddr name)) {
>  	$done->{$_} = $newnet->{$_} if $newnet->{$_};
> @@ -1703,14 +1709,14 @@ sub __mountpoint_mount {
>      my $type = $mountpoint->{type};
>      my $quota = !$snapname && !$mountpoint->{ro} && $mountpoint->{quota};
>      my $mounted_dev;
> -
> +
>      return if !$volid || !$mount;
> 
>      $mount =~ s!/+!/!g;
> 
>      my $mount_path;
>      my ($mpfd, $parentfd, $last_dir);
> -
> +
>      if (defined($rootdir)) {
>  	($rootdir, $mount_path, $mpfd, $parentfd, $last_dir) =
>  	    __mount_prepare_rootdir($rootdir, $mount, $rootuid, $rootgid);
> @@ -1719,7 +1725,7 @@ sub __mountpoint_mount {
>      if (defined($stage_mount)) {
>  	$mount_path = $rootdir;
>      }
> -
> +
>      my ($storage, $volname) = PVE::Storage::parse_volume_id($volid, 1);
> 
>      die "unknown snapshot path for '$volid'" if !$storage && defined($snapname);
> @@ -1828,7 +1834,7 @@ sub __mountpoint_mount {
>  	warn "cannot enable quota control for bind mounts\n" if $quota;
>  	return wantarray ? ($volid, 0, undef) : $volid;
>      }
> -
> +
>      die "unsupported storage";
>  }
> 
> diff --git a/src/PVE/LXC/Config.pm b/src/PVE/LXC/Config.pm
> index af25a96..1d4362e 100644
> --- a/src/PVE/LXC/Config.pm
> +++ b/src/PVE/LXC/Config.pm
> @@ -814,6 +814,11 @@ our $netconf_desc = {
>  	description => "Apply rate limiting to the interface",
>  	optional => 1,
>      },
> +    link_down => {
> +	type => 'boolean',
> +	description => 'Whether this interface should be disconnected (like pulling the plug).',
> +	optional => 1,
> +    },
>  };
>  PVE::JSONSchema::register_format('pve-lxc-network', $netconf_desc);
> 
> diff --git a/src/lxcnetaddbr b/src/lxcnetaddbr
> index 83052e1..d8c6767 100755
> --- a/src/lxcnetaddbr
> +++ b/src/lxcnetaddbr
> @@ -58,7 +58,8 @@ if (-d "/sys/class/net/$iface") {
>      #avoid insecure dependency;
>      ($bridgemtu) = $bridgemtu =~ /(\d+)/;
> 
> -    PVE::Tools::run_command("/sbin/ip link set dev $iface up mtu $bridgemtu");
> +    my $linkstate = defined($net->{link_down}) ? 'down' : 'up';

We need to skip the rest altogether if the link is supposed to stay down
reliably. As mentioned above, a 'down' interface that is still plugged
into a bridge will get activated sooner or later...

> +    PVE::Tools::run_command("/sbin/ip link set dev $iface $linkstate mtu $bridgemtu");
>      PVE::Tools::run_command("/sbin/ip addr add 0.0.0.0/0 dev $iface");
> 
>      if ($have_sdn) {
> --
> 2.39.1