On Mon, Jan 20, 2020 at 5:04 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > On Mon, Jan 20, 2020 at 02:58:01PM +0100, Stefano Garzarella wrote: > > On Mon, Jan 20, 2020 at 1:03 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > On Mon, Jan 20, 2020 at 11:17:35AM +0100, Stefano Garzarella wrote: > > > > On Mon, Jan 20, 2020 at 10:06:10AM +0100, David Miller wrote: > > > > > From: Stefano Garzarella <sgarzare@xxxxxxxxxx> > > > > > Date: Thu, 16 Jan 2020 18:24:26 +0100 > > > > > > > > > > > This patch adds 'netns' module param to enable this new feature > > > > > > (disabled by default), because it changes vsock's behavior with > > > > > > network namespaces and could break existing applications. > > > > > > > > > > Sorry, no. > > > > > > > > > > I wonder if you can even design a legitimate, reasonable, use case > > > > > where these netns changes could break things. > > > > > > > > I forgot to mention the use case. > > > > I tried the RFC with Kata containers and we found that Kata shim-v1 > > > > doesn't work (Kata shim-v2 works as is) because there are the following > > > > processes involved: > > > > - kata-runtime (runs in the init_netns) opens /dev/vhost-vsock and > > > > passes it to qemu > > > > - kata-shim (runs in a container) wants to talk with the guest but the > > > > vsock device is assigned to the init_netns and kata-shim runs in a > > > > different netns, so the communication is not allowed > > > > But, as you said, this could be a wrong design, indeed they already > > > > found a fix, but I was not sure if others could have the same issue. > > > > > > > > In this case, do you think it is acceptable to make this change in > > > > the vsock's behavior with netns and ask the user to change the design? > > > > > > David's question is what would be a usecase that's broken > > > (as opposed to fixed) by enabling this by default. > > > > Yes, I got that. Thanks for clarifying. > > I just reported a broken example that can be fixed with a different > > design (due to the fact that before this series, vsock devices were > > accessible to all netns). > > > > > > > > If it does exist, you need a way for userspace to opt-in, > > > module parameter isn't that. > > > > Okay, but I honestly can't find a case that can't be solved. > > So I don't know whether to add an option (ioctl, sysfs ?) or wait for > > a real case to come up. > > > > I'll try to see better if there's any particular case where we need > > to disable netns in vsock. > > > > Thanks, > > Stefano > > Me neither. so what did you have in mind when you wrote: > "could break existing applications"? I had in mind: 1. the Kata case. It is fixable (the fix is not merged on kata), but older versions will not work with newer Linux. 2. a single process running on init_netns that wants to communicate with VMs handled by VMMs running in different netns, but this case can be solved opening the /dev/vhost-vsock in the same netns of the process that wants to communicate with the VMs (init_netns in this case), and passig it to the VMM. These cases can work with vsock+netns, but they require changes because I'm modifying the vsock behavior with netns.
