[PATCH] kbase: Add knowledge base for libvirt systemtap

[Han Han]

ping, any more reviews?

On Thu, Aug 6, 2020 at 9:44 PM Daniel Henrique Barboza <
danielhb413 at gmail.com> wrote:

>
> On 8/6/20 3:34 AM, Han Han wrote:
> > Signed-off-by: Han Han <hhan at redhat.com>
> > ---
> >   docs/kbase.rst           |   3 ++
> >   docs/kbase/meson.build   |   1 +
> >   docs/kbase/systemtap.rst | 113 +++++++++++++++++++++++++++++++++++++++
> >   3 files changed, 117 insertions(+)
> >   create mode 100644 docs/kbase/systemtap.rst
> >
> > diff --git a/docs/kbase.rst b/docs/kbase.rst
> > index 78daaa5989..d8bff5d41e 100644
> > --- a/docs/kbase.rst
> > +++ b/docs/kbase.rst
> > @@ -36,6 +36,9 @@ Knowledge base
> >         Examination of the security protections used for QEMU and how
> they need
> >         configuring to allow use of QEMU passthrough with host
> files/devices.
> >
> > +   `Systemtap <kbase/systemtap.html>`__
> > +      Explanation of how to use systemtap for libvirt tracing.
> > +
> >      `Virtio-FS <kbase/virtiofs.html>`__
> >         Share a filesystem between the guest and the host
> >
> > diff --git a/docs/kbase/meson.build b/docs/kbase/meson.build
> > index d7f254e163..ca032a4b9b 100644
> > --- a/docs/kbase/meson.build
> > +++ b/docs/kbase/meson.build
> > @@ -13,6 +13,7 @@ docs_kbase_files = [
> >     'rpm-deployment',
> >     's390_protected_virt',
> >     'secureusage',
> > +  'systemtap',
> >     'virtiofs',
> >   ]
> >
> > diff --git a/docs/kbase/systemtap.rst b/docs/kbase/systemtap.rst
> > new file mode 100644
> > index 0000000000..34420efbb2
> > --- /dev/null
> > +++ b/docs/kbase/systemtap.rst
> > @@ -0,0 +1,113 @@
> > +=======================
> > +Systemtap of Libvirt
> > +=======================
> > +
> > +.. contents::
> > +
> > +`Systemtap <https://sourceware.org/systemtap/>`__ is a scripting
> > +language and tool for dynamically probing or tracing in Linux kernel
> > +space or user space. This page is about the usage of systemtap
> > +in libvirt tracing.
> > +
> > +Preparation
> > +===================
> > +
> > +Libvirt
> > +-------------------------
> > +
> > +Libvirt should be configured with the systemtap option to support
> libvirt
> > +probing events in systemtap.
> > +
> > +For libvirt before **6.7.0**, it can be configured by:
> > +
> > +::
> > +
> > +    mkdir build
> > +    cd build
> > +   ../configure --with-dtrace
> > +
> > +For libvirt **6.7.0** or later, configure it by the ``meson`` (seeing
> > +`libvirt compiling <https://libvirt.org/compiling.html>`__):
> > +
> > +::
> > +
> > +   meson build -Ddtrace=enabled
> > +
> > +For the libvirt binaries installed by the package manager like ``dnf``
> or
> > +``apt``, if libvirt systemtap tapset
> ``/usr/share/systemtap/tapset/libvirt_*``
> > +exists, it means the libvirt enables the systemtap feature.
> > +
> > +Systemtap
> > +------------------------
> > +
> > +For most of linux distributions, execute ``stap-prep`` by root to
> prepare the
> > +environment for systemtap after installing the systemtap. If your
> distribution
> > +doesn't have ``stap-prep``, install the ``kernel debuginfo`` packages
> manually.
> > +
> > +After these above, run this test command to confirm the systemtap works
> well:
> > +
> > +::
> > +
> > +   stap -e 'probe oneshot{ printf("hello world\n")}'
> > +
> > +
> > +Tracing events
> > +=======================
> > +
> > +The libvirt systemtap tracing events are defined in tapset
> > +``/usr/share/systemtap/tapset/libvirt_*``. Libvirt support these type
> of tracing
>
> s/type/types
>
> Thanks

>
> With this nit fixed:
>
>
> Reviewed-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
>
>
>
> > +events: ``dbus``, ``event_glib``, ``object``, ``qemu``, ``rpc``.
> > +
> > +List all tracing events in libvirt:
> > +
> > +::
> > +
> > +   grep 'probe libvirt.[a-z_0-9.]*'
> /usr/share/systemtap/tapset/libvirt_* -o|cut -f 2 -d :
> > +
> > +
> > +Tracing examples
> > +==================
> > +
> > +Here is an example of the systemtap script to trace the QMP messages
> sent from libvirtd
> > +daemon to the qemu process.
> > +``qmp.stp``:
> > +
> > +::
> > +
> > +   probe begin
> > +   {
> > +     printf("Start tracing\n")
> > +   }
> > +   probe libvirt.qemu.monitor_send_msg
> > +   {
> > +     printf("QMPs: %s", msg);
> > +   }
> > +
> > +Then run the systemtap script attaching to the libvirtd process:
> > +
> > +::
> > +
> > +   stap qmp.stp -x `pidof libvirtd`
> > +
> > +
> > +To trace a libvirtd started from command line, use the option ``-c``
> > +
> > +::
> > +
> > +   stap qmp.stp -c "/usr/sbin/libvirtd"
> > +
> > +
> > +Then after seeing the welcome message "Start tracing" from systemtap,
> then execute a virsh
> > +command associated with QMP, for example ``virsh domstats``. Then get
> the QMP tracing logs
> > +from systemtap. For example, the result from ``virsh domstats``
> > +
> > +::
> > +
> > +   QMPs: {"execute":"query-balloon","id":"libvirt-393"}
> > +   QMPs:
> {"execute":"qom-get","arguments":{"path":"/machine/peripheral/balloon0","property":"guest-stats"},"id":"libvirt-394"}
> > +   QMPs: {"execute":"query-blockstats","id":"libvirt-395"}
> > +   QMPs: {"execute":"query-named-block-nodes","id":"libvirt-396"}
> > +   QMPs: {"execute":"query-iothreads","id":"libvirt-397"}
> > +
> > +For more examples of libvirt systemtap scripts, see the scripts in
> ``/usr/share/doc/libvirt-docs/examples/systemtap``
> > +For more details of systemtap language, see `document of systemtap <
> https://sourceware.org/systemtap/documentation.html>`__
> >
>
>

-- 
Best regards,
-----------------------------------
Han Han
Senior Quality Engineer
Redhat.

Email: hhan at redhat.com
Phone: +861065339333
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