Re: [PATCH V8 1/6] qapi/net: Add IPFlowSpec and QMP command for COLO passthrough

[Markus Armbruster]

"Zhang, Chen" <chen.zhang@intel.com> writes:

>> -----Original Message-----
>> From: Markus Armbruster <armbru@redhat.com>
>> Sent: Tuesday, June 15, 2021 10:43 PM
>> To: Zhang, Chen <chen.zhang@intel.com>
>> Cc: Jason Wang <jasowang@redhat.com>; qemu-dev <qemu-
>> devel@nongnu.org>; Eric Blake <eblake@redhat.com>; Dr. David Alan
>> Gilbert <dgilbert@redhat.com>; Daniel P.Berrangé <berrange@redhat.com>;
>> Gerd Hoffmann <kraxel@redhat.com>; Li Zhijian <lizhijian@cn.fujitsu.com>;
>> Lukas Straub <lukasstraub2@web.de>; Zhang Chen <zhangckid@gmail.com>
>> Subject: Re: [PATCH V8 1/6] qapi/net: Add IPFlowSpec and QMP command
>> for COLO passthrough
>> 
>> Zhang Chen <chen.zhang@intel.com> writes:
>> 
>> > Since the real user scenario does not need COLO to monitor all traffic.
>> > Add colo-passthrough-add and colo-passthrough-del to maintain a COLO
>> > network passthrough list. Add IPFlowSpec struct for all QMP commands.
>> > All the fields of IPFlowSpec are optional.
>> >
>> > Signed-off-by: Zhang Chen <chen.zhang@intel.com>
>> > ---
>> 
>> The QAPI schema looks good to me, but the interface documentation is still
>> not quite clear enough.  To make progress, I'm going to make concrete
>> suggestions wherever I can despite being quite clueless about the subject
>> matter.  Risks me writing something that's clearer, but wrong.  Keep that in
>> mind, please.
>> 
>> >  net/net.c     | 10 +++++++
>> >  qapi/net.json | 74
>> > +++++++++++++++++++++++++++++++++++++++++++++++++++
>> >  2 files changed, 84 insertions(+)
>> >
>> > diff --git a/net/net.c b/net/net.c
>> > index 76bbb7c31b..f913e97983 100644
>> > --- a/net/net.c
>> > +++ b/net/net.c
>> > @@ -1195,6 +1195,16 @@ void qmp_netdev_del(const char *id, Error **errp)
>> >      }
>> >  }
>> >
>> > +void qmp_colo_passthrough_add(IPFlowSpec *spec, Error **errp) {
>> > +    /* TODO implement setup passthrough rule */ }
>> > +
>> > +void qmp_colo_passthrough_del(IPFlowSpec *spec, Error **errp) {
>> > +    /* TODO implement delete passthrough rule */ }
>> > +
>> >  static void netfilter_print_info(Monitor *mon, NetFilterState *nf)  {
>> >      char *str;
>> > diff --git a/qapi/net.json b/qapi/net.json index
>> > 7fab2e7cd8..91f2e1495a 100644
>> > --- a/qapi/net.json
>> > +++ b/qapi/net.json
>> > @@ -7,6 +7,7 @@
>> >  ##
>> >
>> >  { 'include': 'common.json' }
>> > +{ 'include': 'sockets.json' }
>> >
>> >  ##
>> >  # @set_link:
>> > @@ -696,3 +697,76 @@
>> >  ##
>> >  { 'event': 'FAILOVER_NEGOTIATED',
>> >    'data': {'device-id': 'str'} }
>> > +
>> > +##
>> > +# @IPFlowSpec:
>> > +#
>> > +# IP flow specification.
>> > +#
>> > +# @protocol: Transport layer protocol like TCP/UDP, etc. The protocol is 
>> > the
>> > +#            string instead of enum, because it can be passed to 
>> > getprotobyname(3)
>> > +#            and avoid duplication with /etc/protocols.
>> 
>> The rationale is good, but it doesn't really belong into the interface
>> documentation.  Suggest:
>> 
>>    # @protocol: Transport layer protocol like TCP/UDP, etc.  This will be
>>    #            passed to getprotobyname(3).
>> 
>
> OK.
>
>> 
>> > +#
>> > +# @object-name: The @object-name means packet handler in Qemu. Because not
>> > +#               all the network packet must pass the colo-compare module,
>> > +#               the net-filters are same situation. There modules attach 
>> > to
>> > +#               netdev or chardev to work, VM can run multiple modules
>> > +#               at the same time. So it needs the object-name to set
>> > +#               the effective module.
>> 
>> I still don't understand this, and I'm too ignorant of COLO and networking to
>> suggest improvements.
>
> Let me use qemu boot parameter to clear it.
> For colo-compare, it needs chardev as the source to handle network packet.
> -object 
> colo-compare,id=comp0,primary_in=chardev-input0,secondary_in=chardev-input1,outdev=chardev-output0,iothread=iothread0.
>
> For net filters, it needs attached on netdev.
> -object filter-redirector,id=red0,netdev=hn0,queue=rx,outdev=chardev-output1
> -object filter-mirror,id=mirror0,netdev=hn0,queue=rx,outdev=chardev-output2
>
> And we can use -chardev socket combine the filter and the colo-compare.
>
> Back to the @object-name, One guest maybe have multi colo-compare as the same 
> time, with different object name from different source.
> So we need assign the IPFlowSpec to one object as the handler. Same as the 
> net-filters.
> Each object instance has its own passthrough list.

So the @object-name here references one of the "packet handler objects"
(colo-compare, filter-redirector, filter-mirror) by @id.  Correct?

In other words, @object-name is the ID of a QOM object, and the QOM
object must be of a certain kind (i.e. provide certain functionality).
Correct?

What exactly makes a QOM object a "packet handler object?"

Right now, the packet handler object types are colo-compare,
filter-redirector, filter-mirror, and that's all.  Correct?

Another question the doc comment needs to answer: what happens when
@object-name is absent?

>> Jason or David, perhaps?
>> 
>> > +#
>> > +# @source: Source address and port.
>> > +#
>> > +# @destination: Destination address and port.
>> > +#
>> > +# Since: 6.1
>> > +##
>> > +{ 'struct': 'IPFlowSpec',
>> > +  'data': { '*protocol': 'str', '*object-name': 'str',
>> > +    '*source': 'InetSocketAddressBase',
>> > +    '*destination': 'InetSocketAddressBase' } }
>> > +
>> > +##
>> > +# @colo-passthrough-add:
>> > +#
>> > +# Add passthrough entry IPFlowSpec to the COLO-compare instance.
>> > +# The protocol and source/destination IP/ports are optional. if the
>> > +user # only inputs part of the information, this will match all traffic.
>> 
>> Actually, all arguments are optional.
>> 
>> Suggest:
>> 
>>    # Add an entry to the COLO network passthrough list.
>>    # Absent protocol, host addresses and ports match anything.
>> 
>> If there is more than one such list, then "to a COLO network passthrough 
>> list"
>> instead.
>
> Yes, more than one list.
>
>> 
>> Still missing then: meaning of absent @object-name.  Does it select the COLO
>> network passthrough list, perhaps?
>
> Yes, Please see the explanation above. Each object instance has its own 
> passthrough list.

Got it now.

>> > +#
>> > +# Returns: Nothing on success
>> > +#
>> > +# Since: 6.1
>> > +#
>> > +# Example:
>> > +#
>> > +# -> { "execute": "colo-passthrough-add",
>> > +#      "arguments": { "protocol": "tcp", "object-name": "object0",
>> > +#      "source": {"host": "192.168.1.1", "port": "1234"},
>> > +#      "destination": {"host": "192.168.1.2", "port": "4321"} } }
>> > +# <- { "return": {} }
>> > +#
>> > +##
>> > +{ 'command': 'colo-passthrough-add', 'boxed': true,
>> > +     'data': 'IPFlowSpec' }
>> > +
>> > +##
>> > +# @colo-passthrough-del:
>> > +#
>> > +# Delete passthrough entry IPFlowSpec to the COLO-compare instance.
>> > +# The protocol and source/destination IP/ports are optional. if the
>> > +user # only inputs part of the information, this will match all traffic.
>> 
>> I suspect this command doesn't actually match traffic, it matches entries
>> added with colo-passthrough-add.
>
> Yes.
>
>> 
>> Can it delete more than one such entry?
>> 
>
> Currently no, but it easy to match one more entry to delete.

If the passthrough list entries had some unique ID, we could refer to
one entry by its ID.  It's how things commonly work.

Without an ID, we need to match by value, like you do.  I can see three
possible behaviors:

1. Select first entry that matches.

2. Select all entries that match.

3. If exactly one entry matches, select it.

The second design choice is behavior when nothing gets selected:

a. Silently do nothing

b. Error

Which one did you implement?  My guess based on your answers is 1a.

>> Suggest:
>> 
>>    # Delete an entry from the COLO network passthrough list.
>> 
>> and then explain how the command arguments select entries.
>
> Search the object's passthrough list, if find same entry,  delete it.
>
> Thanks
> Chen
>
>> 
>> > +#
>> > +# Returns: Nothing on success
>> > +#
>> > +# Since: 6.1
>> > +#
>> > +# Example:
>> > +#
>> > +# -> { "execute": "colo-passthrough-del",
>> > +#      "arguments": { "protocol": "tcp", "object-name": "object0",
>> > +#      "source": {"host": "192.168.1.1", "port": "1234"},
>> > +#      "destination": {"host": "192.168.1.2", "port": "4321"} } }
>> > +# <- { "return": {} }
>> > +#
>> > +##
>> > +{ 'command': 'colo-passthrough-del', 'boxed': true,
>> > +     'data': 'IPFlowSpec' }