netdev - Re: [RFC PATCH 0/3] vsock: support network namespace

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Message-ID: <20191203092649.GB153510@stefanha-x1.localdomain>
Date:   Tue, 3 Dec 2019 09:26:49 +0000
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     netdev@...r.kernel.org, linux-hyperv@...r.kernel.org,
        kvm@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
        Dexuan Cui <decui@...rosoft.com>, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jorgen Hansen <jhansen@...are.com>
Subject: Re: [RFC PATCH 0/3] vsock: support network namespace

On Thu, Nov 28, 2019 at 06:15:16PM +0100, Stefano Garzarella wrote:
> Hi,
> now that we have multi-transport upstream, I started to take a look to
> support network namespace (netns) in vsock.
> 
> As we partially discussed in the multi-transport proposal [1], it could
> be nice to support network namespace in vsock to reach the following
> goals:
> - isolate host applications from guest applications using the same ports
>   with CID_ANY
> - assign the same CID of VMs running in different network namespaces
> - partition VMs between VMMs or at finer granularity
> 
> This preliminary implementation provides the following behavior:
> - packets received from the host (received by G2H transports) are
>   assigned to the default netns (init_net)
> - packets received from the guest (received by H2G - vhost-vsock) are
>   assigned to the netns of the process that opens /dev/vhost-vsock
>   (usually the VMM, qemu in my tests, opens the /dev/vhost-vsock)
>     - for vmci I need some suggestions, because I don't know how to do
>       and test the same in the vmci driver, for now vmci uses the
>       init_net
> - loopback packets are exchanged only in the same netns
> 
> Questions:
> 1. Should we make configurable the netns (now it is init_net) where
>    packets from the host should be delivered?

Yes, it should be possible to have multiple G2H (e.g. virtio-vsock)
devices and to assign them to different net namespaces.  Something like
net/core/dev.c:dev_change_net_namespace() will eventually be needed.

> 2. Should we provide an ioctl in vhost-vsock to configure the netns
>    to use? (instead of using the netns of the process that opens
>    /dev/vhost-vsock)

Creating the vhost-vsock instance in the process' net namespace makes
sense.  Maybe wait for a use case before adding an ioctl.

> 3. Should we provide a way to disable the netns support in vsock?

The code should follow CONFIG_NET_NS semantics.  I'm not sure what they
are exactly since struct net is always defined, regardless of whether
network namespaces are enabled.

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