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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
<!--SPDX-License-Identifier: CC-BY-2.0-UK-->
<chapter id='dev-manual-qemu'>
<title>Using the Quick EMUlator (QEMU)</title>
<para>
The Yocto Project uses an implementation of the Quick EMUlator (QEMU)
Open Source project as part of the Yocto Project development "tool
set".
This chapter provides both procedures that show you how to use the
Quick EMUlator (QEMU) and other QEMU information helpful for
development purposes.
</para>
<section id='qemu-dev-overview'>
<title>Overview</title>
<para>
Within the context of the Yocto Project, QEMU is an
emulator and virtualization machine that allows you to run a
complete image you have built using the Yocto Project as just
another task on your build system.
QEMU is useful for running and testing images and applications on
supported Yocto Project architectures without having actual
hardware.
Among other things, the Yocto Project uses QEMU to run automated
Quality Assurance (QA) tests on final images shipped with each
release.
<note>
This implementation is not the same as QEMU in general.
</note>
This section provides a brief reference for the Yocto Project
implementation of QEMU.
</para>
<para>
For official information and documentation on QEMU in general, see
the following references:
<itemizedlist>
<listitem><para>
<emphasis><ulink url='http://wiki.qemu.org/Main_Page'>QEMU Website</ulink>:</emphasis>
The official website for the QEMU Open Source project.
</para></listitem>
<listitem><para>
<emphasis><ulink url='http://wiki.qemu.org/Manual'>Documentation</ulink>:</emphasis>
The QEMU user manual.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='qemu-running-qemu'>
<title>Running QEMU</title>
<para>
To use QEMU, you need to have QEMU installed and initialized as
well as have the proper artifacts (i.e. image files and root
filesystems) available.
Follow these general steps to run QEMU:
<orderedlist>
<listitem><para>
<emphasis>Install QEMU:</emphasis>
QEMU is made available with the Yocto Project a number of
ways.
One method is to install a Software Development Kit (SDK).
See
"<ulink url='&YOCTO_DOCS_SDK_URL;#the-qemu-emulator'>The QEMU Emulator</ulink>"
section in the Yocto Project Application Development and
the Extensible Software Development Kit (eSDK) manual
for information on how to install QEMU.
</para></listitem>
<listitem><para>
<emphasis>Setting Up the Environment:</emphasis>
How you set up the QEMU environment depends on how you
installed QEMU:
<itemizedlist>
<listitem><para>
If you cloned the <filename>poky</filename>
repository or you downloaded and unpacked a
Yocto Project release tarball, you can source
the build environment script (i.e.
<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>):
<literallayout class='monospaced'>
$ cd ~/poky
$ source oe-init-build-env
</literallayout>
</para></listitem>
<listitem><para>
If you installed a cross-toolchain, you can
run the script that initializes the toolchain.
For example, the following commands run the
initialization script from the default
<filename>poky_sdk</filename> directory:
<literallayout class='monospaced'>
. ~/poky_sdk/environment-setup-core2-64-poky-linux
</literallayout>
</para></listitem>
</itemizedlist>
</para></listitem>
<listitem><para>
<emphasis>Ensure the Artifacts are in Place:</emphasis>
You need to be sure you have a pre-built kernel that
will boot in QEMU.
You also need the target root filesystem for your target
machine’s architecture:
<itemizedlist>
<listitem><para>
If you have previously built an image for QEMU
(e.g. <filename>qemux86</filename>,
<filename>qemuarm</filename>, and so forth),
then the artifacts are in place in your
<ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
</para></listitem>
<listitem><para>
If you have not built an image, you can go to the
<ulink url='&YOCTO_MACHINES_DL_URL;'>machines/qemu</ulink>
area and download a pre-built image that matches
your architecture and can be run on QEMU.
</para></listitem>
</itemizedlist></para>
<para>See the
"<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-extracting-the-root-filesystem'>Extracting the Root Filesystem</ulink>"
section in the Yocto Project Application Development and
the Extensible Software Development Kit (eSDK) manual
for information on how to extract a root filesystem.
</para></listitem>
<listitem><para>
<emphasis>Run QEMU:</emphasis>
The basic <filename>runqemu</filename> command syntax is as
follows:
<literallayout class='monospaced'>
$ runqemu [<replaceable>option</replaceable> ] [...]
</literallayout>
Based on what you provide on the command line,
<filename>runqemu</filename> does a good job of figuring
out what you are trying to do.
For example, by default, QEMU looks for the most recently
built image according to the timestamp when it needs to
look for an image.
Minimally, through the use of options, you must provide
either a machine name, a virtual machine image
(<filename>*wic.vmdk</filename>), or a kernel image
(<filename>*.bin</filename>).</para>
<para>Here are some additional examples to help illustrate
further QEMU:
<itemizedlist>
<listitem><para>
This example starts QEMU with
<replaceable>MACHINE</replaceable> set to "qemux86-64".
Assuming a standard
<ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>,
<filename>runqemu</filename> automatically finds the
<filename>bzImage-qemux86-64.bin</filename> image file and
the
<filename>core-image-minimal-qemux86-64-20200218002850.rootfs.ext4</filename>
(assuming the current build created a
<filename>core-image-minimal</filename> image).
<note>
When more than one image with the same name exists, QEMU finds
and uses the most recently built image according to the
timestamp.
</note>
<literallayout class='monospaced'>
$ runqemu qemux86-64
</literallayout>
</para></listitem>
<listitem><para>
This example produces the exact same results as the
previous example.
This command, however, specifically provides the image
and root filesystem type.
<literallayout class='monospaced'>
$ runqemu qemux86-64 core-image-minimal ext4
</literallayout>
</para></listitem>
<listitem><para>
This example specifies to boot an initial RAM disk image
and to enable audio in QEMU.
For this case, <filename>runqemu</filename> set the
internal variable <filename>FSTYPE</filename> to
"cpio.gz".
Also, for audio to be enabled, an appropriate driver must
be installed (see the previous description for the
<filename>audio</filename> option for more information).
<literallayout class='monospaced'>
$ runqemu qemux86-64 ramfs audio
</literallayout>
</para></listitem>
<listitem><para>
This example does not provide enough information for
QEMU to launch.
While the command does provide a root filesystem type, it
must also minimally provide a
<replaceable>MACHINE</replaceable>,
<replaceable>KERNEL</replaceable>, or
<replaceable>VM</replaceable> option.
<literallayout class='monospaced'>
$ runqemu ext4
</literallayout>
</para></listitem>
<listitem><para>
This example specifies to boot a virtual machine
image (<filename>.wic.vmdk</filename> file).
From the <filename>.wic.vmdk</filename>,
<filename>runqemu</filename> determines the QEMU
architecture (<replaceable>MACHINE</replaceable>) to be
"qemux86-64" and the root filesystem type to be "vmdk".
<literallayout class='monospaced'>
$ runqemu /home/scott-lenovo/vm/core-image-minimal-qemux86-64.wic.vmdk
</literallayout>
</para></listitem>
</itemizedlist>
</para></listitem>
</orderedlist>
</para>
</section>
<section id='switching-between-consoles'>
<title>Switching Between Consoles</title>
<para>
When booting or running QEMU, you can switch between
supported consoles by using
Ctrl+Alt+<replaceable>number</replaceable>.
For example, Ctrl+Alt+3 switches you to the serial console
as long as that console is enabled.
Being able to switch consoles is helpful, for example, if
the main QEMU console breaks for some reason.
<note>
Usually, "2" gets you to the main console and "3"
gets you to the serial console.
</note>
</para>
</section>
<section id='removing-the-splash-screen'>
<title>Removing the Splash Screen</title>
<para>
You can remove the splash screen when QEMU is booting by
using Alt+left.
Removing the splash screen allows you to see what is
happening in the background.
</para>
</section>
<section id='disabling-the-cursor-grab'>
<title>Disabling the Cursor Grab</title>
<para>
The default QEMU integration captures the cursor within the
main window.
It does this since standard mouse devices only provide
relative input and not absolute coordinates.
You then have to break out of the grab using the "Ctrl+Alt"
key combination.
However, the Yocto Project's integration of QEMU enables
the wacom USB touch pad driver by default to allow input
of absolute coordinates.
This default means that the mouse can enter and leave the
main window without the grab taking effect leading to a
better user experience.
</para>
</section>
<section id='qemu-running-under-a-network-file-system-nfs-server'>
<title>Running Under a Network File System (NFS) Server</title>
<para>
One method for running QEMU is to run it on an NFS server.
This is useful when you need to access the same file system
from both the build and the emulated system at the same time.
It is also worth noting that the system does not need root
privileges to run.
It uses a user space NFS server to avoid that.
Follow these steps to set up for running QEMU using an NFS
server.
<orderedlist>
<listitem><para>
<emphasis>Extract a Root Filesystem:</emphasis>
Once you are able to run QEMU in your environment, you can
use the <filename>runqemu-extract-sdk</filename> script,
which is located in the <filename>scripts</filename>
directory along with the <filename>runqemu</filename>
script.</para>
<para>The <filename>runqemu-extract-sdk</filename> takes a
root filesystem tarball and extracts it into a location
that you specify.
Here is an example that takes a file system and
extracts it to a directory named
<filename>test-nfs</filename>:
<literallayout class='monospaced'>
runqemu-extract-sdk ./tmp/deploy/images/qemux86-64/core-image-sato-qemux86-64.tar.bz2 test-nfs
</literallayout>
</para></listitem>
<listitem><para>
<emphasis>Start QEMU:</emphasis>
Once you have extracted the file system, you can run
<filename>runqemu</filename> normally with the additional
location of the file system.
You can then also make changes to the files within
<filename>./test-nfs</filename> and see those changes
appear in the image in real time.
Here is an example using the <filename>qemux86</filename>
image:
<literallayout class='monospaced'>
runqemu qemux86-64 ./test-nfs
</literallayout>
</para></listitem>
</orderedlist>
<note>
<para>
Should you need to start, stop, or restart the NFS share,
you can use the following commands:
<itemizedlist>
<listitem><para>
The following command starts the NFS share:
<literallayout class='monospaced'>
runqemu-export-rootfs start <replaceable>file-system-location</replaceable>
</literallayout>
</para></listitem>
<listitem><para>
The following command stops the NFS share:
<literallayout class='monospaced'>
runqemu-export-rootfs stop <replaceable>file-system-location</replaceable>
</literallayout>
</para></listitem>
<listitem><para>
The following command restarts the NFS share:
<literallayout class='monospaced'>
runqemu-export-rootfs restart <replaceable>file-system-location</replaceable>
</literallayout>
</para></listitem>
</itemizedlist>
</para>
</note>
</para>
</section>
<section id='qemu-kvm-cpu-compatibility'>
<title>QEMU CPU Compatibility Under KVM</title>
<para>
By default, the QEMU build compiles for and targets 64-bit and x86
<trademark class='registered'>Intel</trademark> <trademark class='trademark'>Core</trademark>2
Duo processors and 32-bit x86
<trademark class='registered'>Intel</trademark> <trademark class='registered'>Pentium</trademark>
II processors.
QEMU builds for and targets these CPU types because they display
a broad range of CPU feature compatibility with many commonly
used CPUs.
</para>
<para>
Despite this broad range of compatibility, the CPUs could support
a feature that your host CPU does not support.
Although this situation is not a problem when QEMU uses software
emulation of the feature, it can be a problem when QEMU is
running with KVM enabled.
Specifically, software compiled with a certain CPU feature crashes
when run on a CPU under KVM that does not support that feature.
To work around this problem, you can override QEMU's runtime CPU
setting by changing the <filename>QB_CPU_KVM</filename>
variable in <filename>qemuboot.conf</filename> in the
<ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory's</ulink>
<filename>deploy/image</filename> directory.
This setting specifies a <filename>-cpu</filename> option
passed into QEMU in the <filename>runqemu</filename> script.
Running <filename>qemu -cpu help</filename> returns a list of
available supported CPU types.
</para>
</section>
<section id='qemu-dev-performance'>
<title>QEMU Performance</title>
<para>
Using QEMU to emulate your hardware can result in speed issues
depending on the target and host architecture mix.
For example, using the <filename>qemux86</filename> image in the
emulator on an Intel-based 32-bit (x86) host machine is fast
because the target and host architectures match.
On the other hand, using the <filename>qemuarm</filename> image
on the same Intel-based host can be slower.
But, you still achieve faithful emulation of ARM-specific issues.
</para>
<para>
To speed things up, the QEMU images support using
<filename>distcc</filename> to call a cross-compiler outside the
emulated system.
If you used <filename>runqemu</filename> to start QEMU, and the
<filename>distccd</filename> application is present on the host
system, any BitBake cross-compiling toolchain available from the
build system is automatically used from within QEMU simply by
calling <filename>distcc</filename>.
You can accomplish this by defining the cross-compiler variable
(e.g. <filename>export CC="distcc"</filename>).
Alternatively, if you are using a suitable SDK image or the
appropriate stand-alone toolchain is present, the toolchain is
also automatically used.
<note>
Several mechanisms exist that let you connect to the system
running on the QEMU emulator:
<itemizedlist>
<listitem><para>
QEMU provides a framebuffer interface that makes
standard consoles available.
</para></listitem>
<listitem><para>
Generally, headless embedded devices have a serial port.
If so, you can configure the operating system of the
running image to use that port to run a console.
The connection uses standard IP networking.
</para></listitem>
<listitem><para>
SSH servers exist in some QEMU images.
The <filename>core-image-sato</filename> QEMU image
has a Dropbear secure shell (SSH) server that runs
with the root password disabled.
The <filename>core-image-full-cmdline</filename> and
<filename>core-image-lsb</filename> QEMU images
have OpenSSH instead of Dropbear.
Including these SSH servers allow you to use standard
<filename>ssh</filename> and <filename>scp</filename>
commands.
The <filename>core-image-minimal</filename> QEMU image,
however, contains no SSH server.
</para></listitem>
<listitem><para>
You can use a provided, user-space NFS server to boot
the QEMU session using a local copy of the root
filesystem on the host.
In order to make this connection, you must extract a
root filesystem tarball by using the
<filename>runqemu-extract-sdk</filename> command.
After running the command, you must then point the
<filename>runqemu</filename>
script to the extracted directory instead of a root
filesystem image file.
See the
"<link linkend='qemu-running-under-a-network-file-system-nfs-server'>Running Under a Network File System (NFS) Server</link>"
section for more information.
</para></listitem>
</itemizedlist>
</note>
</para>
</section>
<section id='qemu-dev-command-line-syntax'>
<title>QEMU Command-Line Syntax</title>
<para>
The basic <filename>runqemu</filename> command syntax is as
follows:
<literallayout class='monospaced'>
$ runqemu [<replaceable>option</replaceable> ] [...]
</literallayout>
Based on what you provide on the command line,
<filename>runqemu</filename> does a good job of figuring out what
you are trying to do.
For example, by default, QEMU looks for the most recently built
image according to the timestamp when it needs to look for an
image.
Minimally, through the use of options, you must provide either
a machine name, a virtual machine image
(<filename>*wic.vmdk</filename>), or a kernel image
(<filename>*.bin</filename>).
</para>
<para>
Following is the command-line help output for the
<filename>runqemu</filename> command:
<literallayout class='monospaced'>
$ runqemu --help
Usage: you can run this script with any valid combination
of the following environment variables (in any order):
KERNEL - the kernel image file to use
ROOTFS - the rootfs image file or nfsroot directory to use
MACHINE - the machine name (optional, autodetected from KERNEL filename if unspecified)
Simplified QEMU command-line options can be passed with:
nographic - disable video console
serial - enable a serial console on /dev/ttyS0
slirp - enable user networking, no root privileges is required
kvm - enable KVM when running x86/x86_64 (VT-capable CPU required)
kvm-vhost - enable KVM with vhost when running x86/x86_64 (VT-capable CPU required)
publicvnc - enable a VNC server open to all hosts
audio - enable audio
[*/]ovmf* - OVMF firmware file or base name for booting with UEFI
tcpserial=&lt;port&gt; - specify tcp serial port number
biosdir=&lt;dir&gt; - specify custom bios dir
biosfilename=&lt;filename&gt; - specify bios filename
qemuparams=&lt;xyz&gt; - specify custom parameters to QEMU
bootparams=&lt;xyz&gt; - specify custom kernel parameters during boot
help, -h, --help: print this text
Examples:
runqemu
runqemu qemuarm
runqemu tmp/deploy/images/qemuarm
runqemu tmp/deploy/images/qemux86/&lt;qemuboot.conf&gt;
runqemu qemux86-64 core-image-sato ext4
runqemu qemux86-64 wic-image-minimal wic
runqemu path/to/bzImage-qemux86.bin path/to/nfsrootdir/ serial
runqemu qemux86 iso/hddimg/wic.vmdk/wic.qcow2/wic.vdi/ramfs/cpio.gz...
runqemu qemux86 qemuparams="-m 256"
runqemu qemux86 bootparams="psplash=false"
runqemu path/to/&lt;image&gt;-&lt;machine&gt;.wic
runqemu path/to/&lt;image&gt;-&lt;machine&gt;.wic.vmdk
</literallayout>
</para>
</section>
<section id='qemu-dev-runqemu-command-line-options'>
<title><filename>runqemu</filename> Command-Line Options</title>
<para>
Following is a description of <filename>runqemu</filename>
options you can provide on the command line:
<note><title>Tip</title>
If you do provide some "illegal" option combination or perhaps
you do not provide enough in the way of options,
<filename>runqemu</filename> provides appropriate error
messaging to help you correct the problem.
</note>
<itemizedlist>
<listitem><para>
<replaceable>QEMUARCH</replaceable>:
The QEMU machine architecture, which must be "qemuarm",
"qemuarm64", "qemumips", "qemumips64", "qemuppc",
"qemux86", or "qemux86-64".
</para></listitem>
<listitem><para>
<filename><replaceable>VM</replaceable></filename>:
The virtual machine image, which must be a
<filename>.wic.vmdk</filename> file.
Use this option when you want to boot a
<filename>.wic.vmdk</filename> image.
The image filename you provide must contain one of the
following strings: "qemux86-64", "qemux86", "qemuarm",
"qemumips64", "qemumips", "qemuppc", or "qemush4".
</para></listitem>
<listitem><para>
<replaceable>ROOTFS</replaceable>:
A root filesystem that has one of the following
filetype extensions: "ext2", "ext3", "ext4", "jffs2",
"nfs", or "btrfs".
If the filename you provide for this option uses “nfs”, it
must provide an explicit root filesystem path.
</para></listitem>
<listitem><para>
<replaceable>KERNEL</replaceable>:
A kernel image, which is a <filename>.bin</filename> file.
When you provide a <filename>.bin</filename> file,
<filename>runqemu</filename> detects it and assumes the
file is a kernel image.
</para></listitem>
<listitem><para>
<replaceable>MACHINE</replaceable>:
The architecture of the QEMU machine, which must be one
of the following: "qemux86", "qemux86-64", "qemuarm",
"qemuarm64", "qemumips", “qemumips64", or "qemuppc".
The <replaceable>MACHINE</replaceable> and
<replaceable>QEMUARCH</replaceable> options are basically
identical.
If you do not provide a <replaceable>MACHINE</replaceable>
option, <filename>runqemu</filename> tries to determine
it based on other options.
</para></listitem>
<listitem><para>
<filename>ramfs</filename>:
Indicates you are booting an initial RAM disk (initramfs)
image, which means the <filename>FSTYPE</filename> is
<filename>cpio.gz</filename>.
</para></listitem>
<listitem><para>
<filename>iso</filename>:
Indicates you are booting an ISO image, which means the
<filename>FSTYPE</filename> is
<filename>.iso</filename>.
</para></listitem>
<listitem><para>
<filename>nographic</filename>:
Disables the video console, which sets the console to
"ttys0".
This option is useful when you have logged into a server
and you do not want to disable forwarding from the
X Window System (X11) to your workstation or laptop.
</para></listitem>
<listitem><para>
<filename>serial</filename>:
Enables a serial console on
<filename>/dev/ttyS0</filename>.
</para></listitem>
<listitem><para>
<filename>biosdir</filename>:
Establishes a custom directory for BIOS, VGA BIOS and
keymaps.
</para></listitem>
<listitem><para>
<filename>biosfilename</filename>:
Establishes a custom BIOS name.
</para></listitem>
<listitem><para>
<filename>qemuparams=\"<replaceable>xyz</replaceable>\"</filename>:
Specifies custom QEMU parameters.
Use this option to pass options other than the simple
"kvm" and "serial" options.
</para></listitem>
<listitem><para><filename>bootparams=\"<replaceable>xyz</replaceable>\"</filename>:
Specifies custom boot parameters for the kernel.
</para></listitem>
<listitem><para>
<filename>audio</filename>:
Enables audio in QEMU.
The <replaceable>MACHINE</replaceable> option must be
either "qemux86" or "qemux86-64" in order for audio to be
enabled.
Additionally, the <filename>snd_intel8x0</filename>
or <filename>snd_ens1370</filename> driver must be
installed in linux guest.
</para></listitem>
<listitem><para>
<filename>slirp</filename>:
Enables "slirp" networking, which is a different way
of networking that does not need root access
but also is not as easy to use or comprehensive
as the default.
</para></listitem>
<listitem><para id='kvm-cond'>
<filename>kvm</filename>:
Enables KVM when running "qemux86" or "qemux86-64"
QEMU architectures.
For KVM to work, all the following conditions must be met:
<itemizedlist>
<listitem><para>
Your <replaceable>MACHINE</replaceable> must be either
qemux86" or "qemux86-64".
</para></listitem>
<listitem><para>
Your build host has to have the KVM modules
installed, which are
<filename>/dev/kvm</filename>.
</para></listitem>
<listitem><para>
The build host <filename>/dev/kvm</filename>
directory has to be both writable and readable.
</para></listitem>
</itemizedlist>
</para></listitem>
<listitem><para>
<filename>kvm-vhost</filename>:
Enables KVM with VHOST support when running "qemux86"
or "qemux86-64" QEMU architectures.
For KVM with VHOST to work, the following conditions must
be met:
<itemizedlist>
<listitem><para>
<link linkend='kvm-cond'>kvm</link> option
conditions must be met.
</para></listitem>
<listitem><para>
Your build host has to have virtio net device, which
are <filename>/dev/vhost-net</filename>.
</para></listitem>
<listitem><para>
The build host <filename>/dev/vhost-net</filename>
directory has to be either readable or writable
and “slirp-enabled”.
</para></listitem>
</itemizedlist>
</para></listitem>
<listitem><para>
<filename>publicvnc</filename>:
Enables a VNC server open to all hosts.
</para></listitem>
</itemizedlist>
</para>
</section>
</chapter>
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