on 09/04/2012 22:19, Ryan Harper wrote:
* Dan Kenigsberg <dan...@redhat.com> [2012-09-04 05:53]:
On Tue, Sep 04, 2012 at 03:05:37PM +0800, Xu He Jie wrote:
On 09/03/2012 10:33 PM, Dan Kenigsberg wrote:
On Thu, Aug 30, 2012 at 04:26:31PM -0500, Adam Litke wrote:
On Thu, Aug 30, 2012 at 11:32:02AM +0800, Xu He Jie wrote:

   I submited a patch for text-based console

the issue I want to discussing as below:
1. fix port VS dynamic port

Use fix port for all VM's console. connect console with 'ssh
vmUUID@ip -p port'.
Distinguishing VM by vmUUID.

   The current implement was vdsm will allocated port for console
dynamically and spawn sub-process when VM creating.
In sub-process the main thread responsible for accept new connection
and dispatch output of console to each connection.
When new connection is coming, main processing create new thread for
each new connection. Dynamic port will allocated
port for each VM and use range port. It isn't good for firewall rules.

   so I got a suggestion that use fix port. and connect console with
'ssh vmuuid@hostip -p fixport'. this is simple for user.
We need one process for accept new connection from fix port and when
new connection is coming, spawn sub-process for each vm.
But because the console only can open by one process, main process
need responsible for dispatching console's output of all vms and all
So the code will be a little complex then dynamic port.

   So this is dynamic port VS fix port and simple code VS complex code.
>From a usability point of view, I think the fixed port suggestion is nicer.
This means that a system administrator needs only to open one port to enable
remote console access.  If your initial implementation limits console access to
one connection per VM would that simplify the code?
Yes, using a fixed port for all consoles of all VMs seems like a cooler
idea. Besides the firewall issue, there's user experience: instead of
calling getVmStats to tell the vm port, and then use ssh, only one ssh
call is needed. (Taking this one step further - it would make sense to
add another layer on top, directing console clients to the specific host
currently running the Vm.)

I did not take a close look at your implementation, and did not research
this myself, but have you considered using sshd for this? I suppose you
can configure sshd to collect the list of known "users" from
`getAllVmStats`, and force it to run a command that redirects VM's
console to the ssh client. It has a potential of being a more robust
I have considered using sshd and ssh tunnel. They
can't implement fixed port and share console.
Would you elaborate on that? Usually sshd listens to a fixed port 22,
and allows multiple users to have independet shells. What do you mean by
"share console"?

Current implement
we can do anything that what we want.
Yes, it is completely under our control, but there are down sides, too:
we have to maintain another process, and another entry point, instead of
configuring a universally-used, well maintained and debugged
Think of the security implications of having another remote shell
access point to a host.  I'd much rather trust sshd if we can make it


At first glance, the standard sshd on the host is stronger and more robust than a custom ssh server, but the risk using the host sshd is high. If we implement this feature via host ssd, when a hacker attacks the sshd successfully, he will get access to the host shell. After all, the custom ssh server is not for accessing host shell, but just for forwarding the data from the guest console (a host /dev/pts/X device). If we just use a custom ssh server, the code in this server only does 1. auth, 2. data forwarding, when the hacker attacks, he just gets access to that virtual machine. Notice that there is no code written about login to the host in the custom ssh server, and the custom ssh server can be protected under selinux, only allowing it to access /dev/pts/X.

In fact using a custom VNC server in qemu is as risky as a custom ssh server in vdsm. If we accepts the former one, then I can accepts the latter one. The consideration is how robust of the custom ssh server, and the difficulty to maintain it. In He Jie's current patch, the ssh auth and transport library is an open-source third-party project, unless the project is well maintained and well proven, using it can be risky.

So my opinion is using neither the host sshd, nor a custom ssh server. Maybe we can apply the suggestion from Dan Yasny, running a standard sshd in a very small VM in every host, and forward data from this VM to other guest consoles. The ssh part is in the VM, then our work is just forwarding data from the VM via virto serial channels, to the guest via the pty.

Thanks and best regards!

Zhou Zheng Sheng / 周征晟
E-mail: zhshz...@linux.vnet.ibm.com
Telephone: 86-10-82454397

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