[PATCH v2 00/10] NFS: add AF_VSOCK support to NFS client

[Stefan Hajnoczi <stefanha@redhat.com>]

This patch series enables AF_VSOCK address family support in the NFS client.
You can also get the commits from the vsock-nfs branch at
https://github.com/stefanha/linux.git.

The AF_VSOCK address family provides dgram and stream socket communication
between virtual machines and hypervisors.  VMware VMCI and virtio (for KVM)
transports are available, see net/vmw_vsock.

The goal of this work is sharing files between virtual machines and
hypervisors.  AF_VSOCK is well-suited to this because it requires no
configuration inside the virtual machine, making it simple to manage and
reliable.

Why NFS over AF_VSOCK?
----------------------
It is unusual to add a new NFS transport, only TCP, RDMA, and UDP are currently
supported.  Here is the rationale for adding AF_VSOCK.

Sharing files with a virtual machine can be configured manually:
1. Add a dedicated network card to the virtual machine.  It will be used for
   NFS traffic.
2. Configure a local subnet and assign IP addresses to the virtual machine and
   hypervisor
3. Configure an NFS export on the hypervisor and start the NFS server
4. Mount the export inside the virtual machine

Automating these steps poses a problem: modifying network configuration inside
the virtual machine is invasive.  It's hard to add a network interface to an
arbitrary running system in an automated fashion, considering the network
management tools, firewall rules, IP address usage, etc.

Furthermore, the user may disrupt file sharing by accident when they add
firewall rules, restart networking, etc because the NFS network interface is
visible alongside the network interfaces managed by the user.

AF_VSOCK is a zero-configuration network transport that avoids these problems.
Adding it to a virtual machine is non-invasive.  It also avoids accidental
misconfiguration by the user.  This is why "guest agents" and other services in
various hypervisors (KVM, Xen, VMware, VirtualBox) do not use regular network
interfaces.

This is why AF_VSOCK is appropriate for providing shared files as a hypervisor
service.

The approach in this series
---------------------------
AF_VSOCK stream sockets can be used for NFSv4.1 much in the same way as TCP.
RFC 1831 record fragments divide messages since SOCK_STREAM semantics are
present.  The backchannel shares the connection just like the default TCP
configuration.

Addresses are <Context ID, Port Number> pairs.  These patches use "vsock:<cid>"
string representation to distinguish AF_VSOCK addresses from IPv4 and IPv6
numeric addresses.

The following example mounts /export from the hypervisor (CID 2) inside the
virtual machine (CID 3):

  # /sbin/mount.nfs 2:/export /mnt -o clientaddr=3,proto=vsock

Please see the nfs-utils patch series I have just sent to
linux-nfs@vger.kernel.org for the necessary patches.

Status
------
The virtio-vsock transport was merged in Linux 4.8 and the vhost-vsock-pci
device is available in QEMU git master.  This means the underlying AF_VSOCK
transport for KVM is now available upstream.

I have begun work on nfsd support in the kernel and nfs-utils.  This is not
complete yet and will be sent as separate patch series.

Stefan Hajnoczi (10):
  SUNRPC: add AF_VSOCK support to addr.[ch]
  SUNRPC: rename "TCP" record parser to "stream" parser
  SUNRPC: abstract tcp_read_sock() in record fragment parser
  SUNRPC: extract xs_stream_reset_state()
  VSOCK: add tcp_read_sock()-like vsock_read_sock() function
  SUNRPC: add AF_VSOCK support to xprtsock.c
  SUNRPC: drop unnecessary svc_bc_tcp_create() helper
  SUNRPC: add AF_VSOCK support to svc_xprt.c
  SUNRPC: add AF_VSOCK backchannel support
  NFS: add AF_VSOCK support to NFS client

 drivers/vhost/vsock.c                   |   1 +
 fs/nfs/client.c                         |   2 +
 fs/nfs/super.c                          |  11 +-
 include/linux/sunrpc/addr.h             |  44 ++
 include/linux/sunrpc/svc_xprt.h         |  12 +
 include/linux/sunrpc/xprt.h             |   1 +
 include/linux/sunrpc/xprtsock.h         |  36 +-
 include/linux/virtio_vsock.h            |   4 +
 include/net/af_vsock.h                  |   5 +
 include/trace/events/sunrpc.h           |  28 +-
 net/sunrpc/Kconfig                      |  10 +
 net/sunrpc/addr.c                       |  57 +++
 net/sunrpc/svc_xprt.c                   |  18 +
 net/sunrpc/svcsock.c                    |  48 ++-
 net/sunrpc/xprtsock.c                   | 703 +++++++++++++++++++++++++-------
 net/vmw_vsock/af_vsock.c                |  16 +
 net/vmw_vsock/virtio_transport.c        |   1 +
 net/vmw_vsock/virtio_transport_common.c |  66 +++
 net/vmw_vsock/vmci_transport.c          |   8 +
 19 files changed, 880 insertions(+), 191 deletions(-)

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2.7.4