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Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Signed-off-by: Han Han <hhan@redhat.com>
114 lines
3.0 KiB
ReStructuredText
114 lines
3.0 KiB
ReStructuredText
====================
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Systemtap of Libvirt
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====================
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.. contents::
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`Systemtap <https://sourceware.org/systemtap/>`__ is a scripting
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language and tool for dynamically probing or tracing in Linux kernel
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space or user space. This page is about the usage of systemtap
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in libvirt tracing.
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Preparation
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===========
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Libvirt
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-------
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Libvirt should be configured with the systemtap option to support libvirt
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probing events in systemtap.
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For libvirt before **6.7.0**, it can be configured by:
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::
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mkdir build
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cd build
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../configure --with-dtrace
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For libvirt **6.7.0** or later, configure it by the ``meson`` (seeing
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`libvirt compiling <https://libvirt.org/compiling.html>`__):
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::
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meson build -Ddtrace=enabled
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For the libvirt binaries installed by the package manager like ``dnf`` or
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``apt``, if libvirt systemtap tapset ``/usr/share/systemtap/tapset/libvirt_*``
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exists, it means the libvirt enables the systemtap feature.
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Systemtap
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---------
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For most of linux distributions, execute ``stap-prep`` by root to prepare the
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environment for systemtap after installing the systemtap. If your distribution
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doesn't have ``stap-prep``, install the ``kernel debuginfo`` packages manually.
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After these above, run this test command to confirm the systemtap works well:
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::
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stap -e 'probe oneshot{ printf("hello world\n")}'
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Tracing events
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==============
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The libvirt systemtap tracing events are defined in tapset
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``/usr/share/systemtap/tapset/libvirt_*``. Libvirt support these type of tracing
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events: ``dbus``, ``event_glib``, ``object``, ``qemu``, ``rpc``.
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List all tracing events in libvirt:
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::
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grep 'probe libvirt.[a-z_0-9.]*' /usr/share/systemtap/tapset/libvirt_* -o|cut -f 2 -d :
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Tracing examples
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================
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Here is an example of the systemtap script to trace the QMP messages sent from libvirtd
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daemon to the qemu process.
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``qmp.stp``:
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::
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probe begin
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{
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printf("Start tracing\n")
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}
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probe libvirt.qemu.monitor_send_msg
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{
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printf("QMPs: %s", msg);
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}
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Then run the systemtap script attaching to the libvirtd process:
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::
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stap qmp.stp -x `pidof libvirtd`
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To trace a libvirtd started from command line, use the option ``-c``
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::
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stap qmp.stp -c "/usr/sbin/libvirtd"
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Then after seeing the welcome message "Start tracing" from systemtap, then execute a virsh
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command associated with QMP, for example ``virsh domstats``. Then get the QMP tracing logs
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from systemtap. For example, the result from ``virsh domstats``
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::
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QMPs: {"execute":"query-balloon","id":"libvirt-393"}
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QMPs: {"execute":"qom-get","arguments":{"path":"/machine/peripheral/balloon0","property":"guest-stats"},"id":"libvirt-394"}
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QMPs: {"execute":"query-blockstats","id":"libvirt-395"}
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QMPs: {"execute":"query-named-block-nodes","id":"libvirt-396"}
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QMPs: {"execute":"query-iothreads","id":"libvirt-397"}
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For more examples of libvirt systemtap scripts, see the scripts in ``/usr/share/doc/libvirt-docs/examples/systemtap``
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For more details of systemtap language, see `document of systemtap <https://sourceware.org/systemtap/documentation.html>`__
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