2018-01-26 22:03 GMT+08:00 Stefan Hajnoczi <stefanha@xxxxxxxxx>: > On Thu, Jan 25, 2018 at 10:44:12AM -0500, Geneviève Bastien wrote: >> On 2018-01-25 04:29 AM, Stefan Hajnoczi wrote: >> > On Wed, Jan 24, 2018 at 10:56:26AM -0500, Geneviève Bastien wrote: >> >> Thanks for the hint, I didn't know about those. But the uevents are only >> >> for the host right? There is no specific value in debugfs for guest. >> > I'm not sure I understand the question. >> > >> > Uevent are emitted on the host. Given the PID field, it should be >> > possible to correlate them to a specific guest (e.g. by looking at >> > information from the user or VM management tools, or simply by looking >> > at /proc/$PID/cmdline for the QEMU -name argument that can be used to >> > identify guests on the host side). >> > >> > Stefan >> With the information from the host and those uevents, we can indeed >> easily figure out in our traces which processes are associated with a >> guest and get its command line and a lot more information. >> >> The missing piece is in the guest trace. For example, we have lttng >> traces taken on the guest and the host. We may have multiple guests and >> multiple hosts to trace. It's easy to know which traces are from hosts >> from the events, but which are from guests? And which guest trace goes >> with which of the kvm processes on which host? The guest trace contains >> no information that can be linked to the host. >> >> I was thinking that the guest could do a hypercall to the host after >> bootup to share some unique information, for instance its bootid, that >> the host could store somewhere. That information would be available in >> the traces so that we can easily associate the guest with its host >> process and the states of its virtual CPUs to that of the corresponding >> threads, and much more. >> >> I hope this describes our need a little better. > > The QEMU -uuid <uuid> option makes a UUID available to the guest via > SMBIOS and fw_cfg on x86. Inside the guest you can print it like this: > > # dmidecode -s system-uuid > 01020304-0506-0708-090A-0B0C0D0E0F10 > > Maybe you can base the guest trace filename off the UUID: > > guest-01020304-0506-0708-090A-0B0C0D0E0F10-trace-001.dat > > On the host you can either find the UUIDs in the libvirt domain XML: > > # virsh dump my-domain > <domain ...> > <uuid>0102030405060708090a0b0c0d0e0f10</uuid> > ... > > Or you can use the kvm.ko uevent to find the QEMU PID and then check How to use the kvm.ko uevent to find the QEMU PID? Regards, Wanpeng Li
