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

[Bobby Eshleman <bobbyeshleman@gmail.com>]

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:
> > On Fri, Sep 04, 2026 at 10:55:17AM +0200, Stefano Garzarella wrote:
> > > On Wed, Sep 02, 2026 at 04:00:46PM -0700, Bobby Eshleman wrote:
> > > > 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:
> > > 
> > > >
> > > > 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.
> 
> > 
> > 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.

> 
> > 
> > > 
> > > > 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