Re: [PATCH nfs-utils v3 00/14] add NFS over AF_VSOCK support

[Steven Whitehouse <swhiteho@redhat.com>]

Hi,


On 21/09/17 18:00, Stefan Hajnoczi wrote:
> On Tue, Sep 19, 2017 at 01:24:52PM -0400, J. Bruce Fields wrote:
>> On Tue, Sep 19, 2017 at 05:44:27PM +0100, Daniel P. Berrange wrote:
>>> On Tue, Sep 19, 2017 at 11:48:10AM -0400, Chuck Lever wrote:
>>>>> On Sep 19, 2017, at 11:10 AM, Daniel P. Berrange <berrange@redhat.com> wrote:
>>>>> VSOCK requires no guest configuration, it won't be broken accidentally
>>>>> by NetworkManager (or equivalent), it won't be mistakenly blocked by
>>>>> guest admin/OS adding "deny all" default firewall policy. Similar
>>>>> applies on the host side, and since there's separation from IP networking,
>>>>> there is no possibility of the guest ever getting a channel out to the
>>>>> LAN, even if the host is mis-configurated.
>>>> We don't seem to have configuration fragility problems with other
>>>> deployments that scale horizontally.
>>>>
>>>> IMO you should focus on making IP reliable rather than trying to
>>>> move familiar IP-based services to other network fabrics.
>>> I don't see that ever happening, except in a scenario where a single
>>> org is in tight control of the whole stack (host & guest), which is
>>> not the case for cloud in general - only some on-site clouds.
>> Can you elaborate?
>>
>> I think we're having trouble understanding why you can't just say "don't
>> do that" to someone whose guest configuration is interfering with the
>> network interface they need for NFS.
> Dan can add more information on the OpenStack use case, but your
> question is equally relevant to the other use case I mentioned - easy
> file sharing between host and guest.
>
> Management tools like virt-manager (https://virt-manager.org/) should
> support a "share directory with VM" feature.  The user chooses a
> directory on the host, a mount point inside the guest, and then clicks
> OK.  The directory should appear inside the guest.
>
> VMware, VirtualBox, etc have had file sharing for a long time.  It's a
> standard feature.
>
> Here is how to implement it using AF_VSOCK:
> 1. Check presence of virtio-vsock device in VM or hotplug it.
> 2. Export directory from host NFS server (nfs-ganesha, nfsd, etc).
> 3. Send qemu-guest-agent command to (optionally) add /etc/fstab entry
>     and then mount.
>
> The user does not need to take any action inside the guest.
> Non-technical users can share files without even knowing what NFS is.
>
> There are too many scenarios where guest administrator action is
> required with NFS over TCP/IP.  We can't tell them "don't do that"
> because it makes this feature unreliable.
>
> Today we ask users to set up NFS or CIFS themselves.  In many cases that
> is inconvenient and an easy file sharing feature would be much better.
>
> Stefan
>

I don't think we should give up on making NFS easy to use with TCP/IP in 
such situations. With IPv6 we could have (for example) a device with a 
well known link-local address at the host end, and an automatically 
allocated link-local address at the guest end. In other words the same 
as VSOCK, but with IPv6 rather than VSOCK addresses. At that point the 
remainder of the NFS config steps would be identical to those you've 
outlined with VSOCK above.

Creating a (virtual) network device which is restricted to host/guest 
communication and automatically configures itself should be a lot less 
work than adding a whole new protocol to NFS I think. It could also be 
used for many other use cases too, as well as giving the choice between 
NFS and CIFS. So it is much more flexible, and should be quicker to 
implement too,

Steve.