Re: [Qemu-devel] [POC] colo-proxy in qemu

[Jason Wang <jasowang@redhat.com>]

On 07/20/2015 02:42 PM, Li Zhijian wrote:
> Hi, all
>
> We are planning to implement colo-proxy in qemu to cache and compare
> packets.
> This module is one of the important component of COLO project and now
> it is
> still in early stage, so any comments and feedback are warmly welcomed,
> thanks in advance.
>
> ## Background
> COLO FT/HA (COarse-grain LOck-stepping Virtual Machines for Non-stop
> Service)
> project is a high availability solution. Both Primary VM (PVM) and
> Secondary VM
> (SVM) run in parallel. They receive the same request from client, and
> generate
> responses in parallel too. If the response packets from PVM and SVM are
> identical, they are released immediately. Otherwise, a VM checkpoint
> (on demand)
> is conducted.
> Paper:
> http://www.socc2013.org/home/program/a3-dong.pdf?attredirects=0
> COLO on Xen:
> http://wiki.xen.org/wiki/COLO_-_Coarse_Grain_Lock_Stepping
> COLO on Qemu/KVM:
> http://wiki.qemu.org/Features/COLO
>
> By the needs of capturing response packets from PVM and SVM and
> finding out
> whether they are identical, we introduce a new module to qemu
> networking called
> colo-proxy.

A question here, the packet comparing may be very tricky. For example,
some protocol use random data to generate unpredictable id or something
else. One example is ipv6_select_ident() in Linux. So COLO needs a
mechanism to make sure PVM and SVM can generate same random data?