Re: qmp-shell TUI (was: Re: Call for Google Summer of Code 2021 project ideas)

Am 14.01.2021 um 14:59 hat Daniel P. Berrangé geschrieben: > On Thu, Jan 14, 2021 at 01:52:34PM +0000, Stefan Hajnoczi wrote: > > On Wed, Jan 13, 2021 at 01:59:43PM -0500, John Snow wrote: > > > On 1/13/21 3:53 AM, Stefan Hajnoczi wrote: > > > > On Tue, Jan 12, 2021 at 9:10 PM John Snow <jsnow(a)redhat.com&gt; wrote: > > > > 2. Ability to watch QMP activity on a running QEMU process, e.g. even > > > > when libvirt is directly connected to the monitor. > > > > > > > > > > That *WOULD* be extremely cool, and moves a lot closer to how mitmproxy > > > works. > > > > > > (Actually, mitmproxy could theoretically be taught how to read and > > > understand QMP traffic, but that's not something I know how to do or would > > > be prepared to mentor.) > > > > > > Is this possible to do in a post-hoc fashion? Let's say you are using > > > production environment QEMU, how do we attach the QMP listener to it? Or > > > does this idea require that we start QEMU in a specific fashion with a > > > second debug socket that qmp-shell can connect to in order to listen? > > > > > > ... Or do we engineer qmp-shell to open its own socket that libvirt connects > > > to ...? > > > > Here is the QEMU command-line that libvirt uses on my F33 system: > > > > -chardev socket,id=charmonitor,fd=36,server,nowait > > -mon chardev=charmonitor,id=monitor,mode=control > > > > Goals for this feature: > > > > 1. No manual steps required for setup. > > 2. Ability to start/stop monitoring traffic at runtime without > > restarting QEMU. > > 3. Available to unprivileged users. > > > > I think the easiest way to achieve this is through a new QEMU monitor > > command. Approaches that come to mind: > > > > 1. Add a -mon debug-chardev property and a QMP command to set it at > > runtime. The debug-chardev receives both monitor input (commands) and > > output (responses and events). This does not allow MITM, rather it > > mirrors traffic. > > > > 2. Add a chardev-get-fd command that fetches the fd from a chardev and > > then use the existing chardev-change command to replace the monitor > > chardev with a chardev connected to qmp-shell. This inserts qmp-shell > > as a proxy between the QMP client and server. qmp-shell can remove > > itself again with another chardev-change command. This approach > > allows MITM. The downside is it assumes the QMP chardev is a file > > descriptor, so it won't work with all types of chardev. > > > > 3. Add a new chardev-proxy type that aggregates 3 chardevs: 1. an origin > > source chardev, 2. a monitoring sink chardev, and 3. a monitoring > > source chardev. The data flow is origin <-> monitoring sink <-> > > monitoring source <-> QMP monitor. qmp-shell creates the monitoring > > sink (for receiving incoming QMP commands) and monitoring source > > chardev (for forwarding QMP commands or MITM commands), and then it > > uses change-chardev to instantiate a chardev-proxy that directs the > > original libvirt chardev through the monitoring sink and source. > > > > This is the most complex but also completely contained within the > > QEMU chardev layer. I have an idea for the QMP command name: chardev-snapshot-sync! Finally we get backing file chains for chardevs! :-)

> > In all these approaches qmp-shell uses virsh qemu-monitor-command or an > > equivalent API to start/stop monitoring a running VM without manual > > setup steps. > > Why go to the trouble of adding more chardevs to a running QEMU that > libvirt has. qmp-shell can just directly use the libvirt Python API > to invoke virDomainQemuMonitorCommand to invoke QMP commands, and > the othe API for receiving QMP events. > > Essentially it just needs to be split into two layers. The upper > layer works in terms of individual QMP command/replies, and QMP > events. The lower layer provides a transport that is either a > UNIX socket, or is the libvirt QMP passthrough API. > > Or alternatively, provide a virt-qmp-shim command that listens on > a UNIX socket, accepts QMP commands and turns them into calls to > virDomainQemuMonitorCommand, and funnells back the response. I think the idea was to show the QMP traffic that libvirt produces for other management applications, not for the QMP shell. These APIs probably don't allow this?