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[Bug runtime/13078] investigate qemu virtio-serial channel for talking to stap-sh
- From: "jlebon at redhat dot com" <sourceware-bugzilla at sourceware dot org>
- To: systemtap at sourceware dot org
- Date: Fri, 30 Aug 2013 20:37:49 +0000
- Subject: [Bug runtime/13078] investigate qemu virtio-serial channel for talking to stap-sh
- Auto-submitted: auto-generated
- References: <bug-13078-6586 at http dot sourceware dot org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=13078
--- Comment #11 from Jonathan Lebon <jlebon at redhat dot com> ---
I created a udev rules file as well as a systemd template service file which
placed together in the VM spawns a stapsh instance for each detected port of
the type org.systemtap.[0-9]* (naming not formalized yet). Pretty sweet!
So all we would need to do is to make these files part of systemtap-runtime for
users to install in their VM (no added dependencies!) and on the host side have
stap-vm add the ports to the VM's definition to get the whole thing working.
For systems that do not have systemd, we can have a simple bash script which
looks for any of the org.systemtap.* ports and starts up one stapsh for each of
them (or exits if no ports are found). It would be helpful to make this script
long-lived, respawning any of the stapsh instances as they exit.
A minor issue is SELinux. It blocks qemu from creating sockets anywhere other
than in a directory with the qemu_var_run_t context. One good location
satisfying this is /var/lib/libvirt/qemu (recommended by dberrange in
BZ598533#c6).
The last major hurdle left is permissions. We have no issues on the guest side
since systemd/init spawns stapsh. However, on the host side, the UNIX socket is
created with qemu:qemu 755. There are no options to change this. These
permissions come from a umask(022) call in libvirtd, which qemu then inherits.
I'll have to contact the libvirt guys to see if they have any ideas.
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