Re: [PATCH net-next 0/6] vsock: assign the guest vsock device to a network namespace

On Tue, Sep 15, 2026 at 12:16:47PM +0200, Stefano Garzarella wrote:

On Fri, Sep 04, 2026 at 10:30:28AM -0700, Bobby Eshleman wrote:

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On Fri, Sep 04, 2026 at 10:55:17AM +0200, Stefano Garzarella wrote:

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On Wed, Sep 02, 2026 at 04:00:46PM -0700, Bobby Eshleman wrote:

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vsock network namespaces let a host put each VM in a namespace of its
own. A guest has no equivalent yet. It has a single G2H device that
cannot be assigned to a network namespace.

Thanks for this, I'll do a proper review next week, in the mean time some
comments below:

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This series lets a guest move that device into a network namespace. A
new ioctl on /dev/vsock, IOCTL_VM_SOCKETS_ASSIGN_G2H_NETNS, assigns the
device to the namespace of the calling process. The namespace's existing

Why an ioctl?

I'm asking because I'd like to know if you've already considered any
alternatives (sysfs, netlink, etc.)

How do you think the ioctl should be used? Should we provide an userspace
tool, or extending some existing tools?

Thanks,
Stefano

Really only because /dev/vsock exists and the prior series used it.

Yeah, I vaguely remember that we may have discussed switching to netlink in
that thread, but I can't find it.

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Considering netlink, it might be the better option because there is a
lot of prior art solving problems we might have in the future. For
example, I was thinking about when users suddenly lose access to vsock,
with just the current assign ioctl there is no way for apps or users to
figure out why this happened. We can have an ioctl() setter for user,
but in netdev world users can actually get a notification via netlink as
to which namespace the device went to and what its ifindex is there (see
__dev_change_net_namespace() for the RTM_DELLINK and RTM_NEWLINK
messages). There is probably more, but that's the case that comes to
mind.

netlink seems like the right way to go, do you think it'll be a real pain to
implement?

It is really not bad... it'll include a yaml spec in
Documentation/netlink/specs/ of call names and perms, a new target for
generated code in the Makefile, a handler, and then
tools/net/ynl/ynl-regen.sh generates the plumbing.

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ns_mode then decides who may use it: a "global" namespace shares the
device with every other global namespace, and a "local" namespace keeps
the host connection to itself. The device starts out in the initial
namespace, so until the ioctl is issued nothing has moved and no mode
has changed. There is no explicit unassign as assigning the device back
to the initial namespace is equivalent.

The ioctl requires CAP_NET_ADMIN in the initial user namespace.

Connections that can no longer reach the device after a move are reset,
so that a namespace which has lost access cannot keep using a socket it
opened while it still had access. Following netdevs, the device returns
to the initial namespace when the namespace it was moved to is deleted.

Transports opt in through a new netns_assign_allow callback. Only
virtio-vsock implements it here.

Why? (Not asking to support all the others, asking to explain the reason or
ask helps from others to extend it)

Thanks,
Stefano

Sure, can add a note here about extending it. I just didn't want to
implement code without having an environment allowing me to test it.

It's fine, I'm not asking you to do it ;-)

Sorry again for the delay, I hope to review this series today/tomorrow.

Thanks,
Stefano

No rush!

Thanks,
Bobby