[PATCH] kbase: Add knowledge base for libvirt systemtap

[Daniel Henrique Barboza]

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


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>`__
>