[pve-devel] [PATCH v3 container/manager 0/4] fix #3413: Add `Disconnect` option for LXC networks

Christoph Heiss c.heiss at proxmox.com
Tue Feb 21 09:05:46 CET 2023

Add a `Disconnect` option for network interfaces on LXC containers, much
like it already exists for VMs. This has been requested in #3413 [0] and
seems useful, especially considering we already support the same thing
for VMs.

One thing to note is that LXC does not seem to support the notion of
setting an interface down. The `flags` property would suggest that this
possible [1], but AFAICS it does not work. I tried setting the value as
empty and to something else than "up" (since that is really the only
supported option [2][3]), which both had absolutely no effect.

Thus force the host-side link of the container network down and avoid
adding it to the designated bridge if the new option is set, effectively
disconnecting the container network.

The first two patches are cleanup-patches only and do not change
anything regarding functionality.

Testing was done by starting a LXC container (w/ and w/o `link_down`
set), checking if the interface has (or not) LOWERLAYERDOWN set inside
the container (`ip address eth0`) and if packet transit works (or not)
using a simple `ping`. Same thing after toggeling the option on the
interface.  Further, the interface(s) should (or should not) be listed
in `brctl show`. Same thing was done for hotplugged interfaces to a
running container.

Also tested with `ifreload -a` (thanks Wolfgang!) thrown in, which did
nothing unexpected: If `link_down` was set, interfaces stayed in
LOWERLAYERDOWN and unplugged from the bridge, and stayed UP and plugged
into the bridge when `link_down` was unset.

[0] https://bugzilla.proxmox.com/show_bug.cgi?id=3413
[1] https://linuxcontainers.org/lxc/manpages/man5/lxc.container.conf.5.html#lbAO
[2] https://github.com/lxc/lxc/blob/08f0e769/src/lxc/confile.c#L453-L467
[3] https://github.com/lxc/lxc/blob/08f0e769/src/lxc/confile.c#L5933-L5952

v1: https://lists.proxmox.com/pipermail/pve-devel/2023-February/055762.html
v2: https://lists.proxmox.com/pipermail/pve-devel/2023-February/055795.html


Christoph Heiss (3):
      lxc: Fix some trailing whitespace
      lxc: Avoid open-coding normal vs SDN-specific tap_plug()
      lxc: Add `link_down` config to allow setting interfaces as disconnected

 src/PVE/LXC.pm        | 41 ++++++++++++++++++++++++++++++++++-------
 src/PVE/LXC/Config.pm |  6 ++++++
 src/lxcnetaddbr       |  7 +++++--
 3 files changed, 45 insertions(+), 9 deletions(-)


Christoph Heiss (1):
      lxc: Add `Disconnect` option for network interfaces

 www/manager6/Parser.js      |  3 +++
 www/manager6/lxc/Network.js | 13 +++++++++++++
 2 files changed, 16 insertions(+)


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