Re: [PATCH net-next v1 1/3] vm_sockets: Include flag field in the vsock address data structure

[Stefano Garzarella]

On Tue, Dec 01, 2020 at 08:15:04PM +0200, Paraschiv, Andra-Irina wrote:
> On 01/12/2020 18:09, Stefano Garzarella wrote:
> > On Tue, Dec 01, 2020 at 05:25:03PM +0200, Andra Paraschiv wrote:
> > > vsock enables communication between virtual machines and the host they
> > > are running on. With the multi transport support (guest->host and
> > > host->guest), nested VMs can also use vsock channels for communication.
> > >
> > > In addition to this, by default, all the vsock packets are forwarded to
> > > the host, if no host->guest transport is loaded. This behavior can be
> > > implicitly used for enabling vsock communication between sibling VMs.
> > >
> > > Add a flag field in the vsock address data structure that can be used to
> > > explicitly mark the vsock connection as being targeted for a certain
> > > type of communication. This way, can distinguish between nested VMs and
> > > sibling VMs use cases and can also setup them at the same time. Till
> > > now, could either have nested VMs or sibling VMs at a time using the
> > > vsock communication stack.
> > >
> > > Use the already available "svm_reserved1" field and mark it as a flag
> > > field instead. This flag can be set when initializing the vsock address
> > > variable used for the connect() call.
> >
> > Maybe we can split this patch in 2 patches, one to rename the svm_flag
> > and one to add the new flags.
>
> Sure, I can split this in 2 patches, to have a bit more separation of 
> duties.
>
> > > Signed-off-by: Andra Paraschiv <andraprs@xxxxxxxxxx>
> > > ---
> > > include/uapi/linux/vm_sockets.h | 18 +++++++++++++++++-
> > > 1 file changed, 17 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/uapi/linux/vm_sockets.h 
> > > b/include/uapi/linux/vm_sockets.h
> > > index fd0ed7221645d..58da5a91413ac 100644
> > > --- a/include/uapi/linux/vm_sockets.h
> > > +++ b/include/uapi/linux/vm_sockets.h
> > > @@ -114,6 +114,22 @@
> > >
> > > #define VMADDR_CID_HOST 2
> > >
> > > +/* This sockaddr_vm flag value covers the current default use case:
> > > + * local vsock communication between guest and host and nested 
> > > VMs setup.
> > > + * In addition to this, implicitly, the vsock packets are 
> > > forwarded to the host
> > > + * if no host->guest vsock transport is set.
> > > + */
> > > +#define VMADDR_FLAG_DEFAULT_COMMUNICATION     0x0000
> >
> > I think we don't need this macro, since the next one can be used to
> > check if it a sibling communication (flag 0x1 set) or not (flag 0x1
> > not set).
>
> Right, that's not particularly the use of the flag value, as by 
> default comes as 0. It was more for sharing the cases this covers. But 
> I can remove the define and keep this kind of info, with regard to the 
> default case, in the commit message / comments.

Agree, you can add few lines in the comment block of VMADDR_FLAG_SIBLING 
describing the default case when it is not set.

> > > +
> > > +/* Set this flag value in the sockaddr_vm corresponding field if 
> > > the vsock
> > > + * channel needs to be setup between two sibling VMs running on 
> > > the same host.
> > > + * This way can explicitly distinguish between vsock channels 
> > > created for nested
> > > + * VMs (or local communication between guest and host) and the 
> > > ones created for
> > > + * sibling VMs. And vsock channels for multiple use cases (nested 
> > > / sibling VMs)
> > > + * can be setup at the same time.
> > > + */
> > > +#define VMADDR_FLAG_SIBLING_VMS_COMMUNICATION 0x0001
> >
> > What do you think if we shorten in VMADDR_FLAG_SIBLING?
>
> Yup, this seems ok as well for me. I'll update the naming.

Thanks,
Stefano