Re: [PATCH net-next v8 06/14] vsock/virtio: add netns to virtio transport common

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Thu, Nov 06, 2025 at 05:20:05PM +0100, Stefano Garzarella wrote:
> On Thu, Oct 23, 2025 at 11:27:45AM -0700, Bobby Eshleman wrote:
> > From: Bobby Eshleman <bobbyeshleman@meta.com>
> > 
> > Enable network namespace support in the virtio-vsock common transport
> > layer by declaring namespace pointers in the transmit and receive
> > paths.
> > 
> > The changes include:
> > 1. Add a 'net' field to virtio_vsock_pkt_info to carry the namespace
> >   pointer for outgoing packets.
> > 2. Store the namespace and namespace mode in the skb control buffer when
> >   allocating packets (except for VIRTIO_VSOCK_OP_RST packets which do
> >   not have an associated socket).
> > 3. Retrieve namespace information from skbs on the receive path for
> >   lookups using vsock_find_connected_socket_net() and
> >   vsock_find_bound_socket_net().
> > 
> > This allows users of virtio transport common code
> > (vhost-vsock/virtio-vsock) to later enable namespace support.
> > 
> > Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
> > ---
> > Changes in v7:
> > - add comment explaining the !vsk case in virtio_transport_alloc_skb()
> > ---
> > include/linux/virtio_vsock.h            |  1 +
> > net/vmw_vsock/virtio_transport_common.c | 21 +++++++++++++++++++--
> > 2 files changed, 20 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > index 29290395054c..f90646f82993 100644
> > --- a/include/linux/virtio_vsock.h
> > +++ b/include/linux/virtio_vsock.h
> > @@ -217,6 +217,7 @@ struct virtio_vsock_pkt_info {
> > 	u32 remote_cid, remote_port;
> > 	struct vsock_sock *vsk;
> > 	struct msghdr *msg;
> > +	struct net *net;
> > 	u32 pkt_len;
> > 	u16 type;
> > 	u16 op;
> > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > index dcc8a1d5851e..b8e52c71920a 100644
> > --- a/net/vmw_vsock/virtio_transport_common.c
> > +++ b/net/vmw_vsock/virtio_transport_common.c
> > @@ -316,6 +316,15 @@ static struct sk_buff *virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *
> > 					 info->flags,
> > 					 zcopy);
> > 
> > +	/*
> > +	 * If there is no corresponding socket, then we don't have a
> > +	 * corresponding namespace. This only happens For VIRTIO_VSOCK_OP_RST.
> > +	 */
> 
> So, in virtio_transport_recv_pkt() should we check that `net` is not set?
> 
> Should we set it to NULL here?
> 

Sounds good to me.

> > +	if (vsk) {
> > +		virtio_vsock_skb_set_net(skb, info->net);
> 
> Ditto here about the net refcnt, can the net disappear?
> Should we use get_net() in some way, or the socket will prevent that?
> 

As long as the socket has an outstanding skb it can't be destroyed and
so will have a reference to the net, that is after skb_set_owner_w() and
freeing... so I think this is okay.

But, maybe we could simplify the implied relationship between skb, sk,
and net by removing the VIRTIO_VSOCK_SKB_CB(skb)->net entirely, and only
ever referring to sock_net(skb->sk)? I remember originally having a
reason for adding it to the cb, but my hunch is it that it was probably
some confusion over the !vsk case.

WDYT?

[...]

> > 
> > 	return virtio_transport_send_pkt_info(vsk, &info);
> > @@ -1578,7 +1593,9 @@ static bool virtio_transport_valid_type(u16 type)
> > void virtio_transport_recv_pkt(struct virtio_transport *t,
> > 			       struct sk_buff *skb)
> > {
> > +	enum vsock_net_mode net_mode = virtio_vsock_skb_net_mode(skb);
> > 	struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
> > +	struct net *net = virtio_vsock_skb_net(skb);
> 
> Okay, so this is where the skb net is read, so why we touch the virtio-vsock
> driver (virtio_transport.c) in the other patch where we changed just
> af_vsock.c?
> 
> IMO we should move that change here, or in a separate commit.
> Or maybe I missed some dependency :-)
> 

100% agree.

> Thanks,
> Stefano
> 

Thanks!

-Bobby