[systemd-devel] systemd-nspawn: cannot join existing macvlan

Kai Krakow hurikhan77 at gmail.com
Fri May 8 11:53:01 PDT 2015

Kai Krakow <hurikhan77 at gmail.com> schrieb:

> Kai Krakow <hurikhan77 at gmail.com> schrieb:
> Hello again!

And again...

> Amended below...
>> I'm not sure about this but I suspect that I cannot start a second nspawn
>> container with --network-macvlan when another nspawn instance has created
>> it before:
>> # systemd-nspawn -b --network-macvlan=enp4s0
>> Spawning container gentoo-mysql-base on
>> /var/lib/machines/gentoo-mysql-base. Press ^] three times within 1s to
>> kill container. Failed to add new macvlan interfaces: File exists
>> To my surprise it works when adding machines to machines.target. While
>> you cannot start them through means of systemd because of the same error,
>> it works during boot of the whole system: All containers boot up properly
>> - but stop one and you cannot restart it.
>> So it looks like there's an unintentional race condition during boot
>> which allows to create this interface but when the system is up, it no
>> longer works because the race condition is no longer present.
>> systemd-nspawn should probably just allow joining existing macvlan
>> bridges. I would fix it in the code but I don't know the implications why
>> this check is in there in the first place.
>> A second fix should maybe do something about such race conditions if it
>> is such one. I suspect there are cases where the interface presence check
>> makes actually sense.
> I installed something which is called a stable v219 snapshot, I could not
> find out which changes are included, tho:
> *systemd-219_p112 (26 Apr 2015)
>   26 Apr 2015; Mike Gilbert <floppym at gentoo.org> +systemd-219_p112.ebuild:
>   Add a snapshot from the v219-stable branch upstream.
> The behavior described above has changed with this snapshot: Machines
> using macvlan no longer start, even not a boot-up (which worked before).
> The error is still the same:
> # systemd-nspawn -b --link-journal=try-guest --network-macvlan=enp4s0 --
> bind=/usr/portage --bind-ro=/usr/src --machine=test
> Spawning container test on /var/lib/machines/test.
> Press ^] three times within 1s to kill container.
> Failed to add new macvlan interfaces: File exists
> I still don't think that systemd-nspawn should insist on creating the
> host- side macvlan bridge and fail, if it cannot. It should just accept
> that it is already there.

My findings show that it actually does accept this case. But I had to 
explicitly order the machines after network.target to successfully start at 
boot time.

It looks fine so far. The stable snapshot of v219 mentioned above seems to 
actually have fixed a few issues.

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