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ref-manual/variables.rst: document qemuboot variables

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Document the variables in qemuboot.bbclass that allow customizing how
the QEMU guest is instantiated.

(From yocto-docs rev: 3c485a4838d7ca721d2d00867ff3d98d9e999c69)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
(cherry picked from commit 392ef512b05da8170d5e329c2750b2ada0a06cbd)
[AG: remove QB_TAP_NAMESERVER, doesn't exist on scarthgap]
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Paul Barker <paul@pbarker.dev>
This commit is contained in:
Antonin Godard
2026-02-20 11:17:26 +01:00
committed by Paul Barker
parent 5a83b18b4d
commit 3cd1dbb582
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@@ -7360,6 +7360,148 @@ system and gives an overview of their function and contents.
QA_EMPTY_DIRS_RECOMMENDATION:/dev = "but all devices must be created at runtime"
:term:`QB_CMDLINE_IP_SLIRP`
If :term:`QB_NETWORK_DEVICE` adds more than one network interface to QEMU,
usually the ``ip=`` Linux kernel command line argument needs to be changed
accordingly. The :term:`QB_CMDLINE_IP_SLIRP` variable allows controlling
this value. See the Linux kernel documentation for more details:
https://www.kernel.org/doc/Documentation/filesystems/nfs/nfsroot.txt.
:term:`QB_CMDLINE_IP_TAP`
This variable is similar to the :term:`QB_CMDLINE_IP_SLIRP` variable.
Use as follows::
QB_CMDLINE_IP_TAP = "ip=192.168.7.@CLIENT@::192.168.7.@GATEWAY@:255.255.255.0::eth0"
Since the tap interface requires static IP configuration, ``runqemu``
replaces the ``@CLIENT@`` and ``@GATEWAY@`` place holders by the IP and
the gateway address of the QEMU guest.
:term:`QB_DEFAULT_FSTYPE`
The :term:`QB_DEFAULT_FSTYPE` variable controls the default filesystem
type to boot. It is represented as the file extension of one of the root
filesystem image extension found in :term:`DEPLOY_DIR_IMAGE`. For example:
``ext4.zst``.
:term:`QB_DEFAULT_KERNEL`
When using ``runqemu``, the :term:`QB_DEFAULT_KERNEL` variable controls
the default Linux kernel image to boot, found in :term:`DEPLOY_DIR_IMAGE`. For
example: ``bzImage``.
:term:`QB_DRIVE_TYPE`
When using ``runqemu``, the :term:`QB_DRIVE_TYPE` variable specifies the
type of drive to emulate when starting the emulated machine.
Valid values are:
- ``/dev/hd``: emulates an IDE drive.
- ``/dev/mmcblk``: emulates an SD Card.
- ``/dev/sd``: emulates an SCSI drive.
- ``/dev/vd``: emulates a VirtIO drive.
- ``/dev/vdb``: emulates a block VirtIO drive.
:term:`QB_GRAPHICS`
When using ``runqemu``, the :term:`QB_GRAPHICS` variable controls the QEMU
video card type to emulate. For example: ``-vga std``.
This value is appended to the argument list when running ``qemu``.
:term:`QB_KERNEL_CMDLINE_APPEND`
The :term:`QB_KERNEL_CMDLINE_APPEND` variable controls the options passed
to the Linux kernel's ``-append`` QEMU options, which controls the Linux kernel
command-line.
For example::
QB_KERNEL_CMDLINE_APPEND = "console=ttyS0"
:term:`QB_MEM`
The :term:`QB_MEM` variable controls the amount of memory allocated to the
emulated machine. Specify as follows::
QB_MEM = "-m 512"
:term:`QB_NETWORK_DEVICE`
When using ``runqemu``, the :term:`QB_NETWORK_DEVICE` variable controls
the network device instantiated by QEMU. This value needs to be compatible
with the :term:`QB_TAP_OPT` variable.
Example::
QB_NETWORK_DEVICE = "-device virtio-net-pci,netdev=net0,mac=@MAC@"
``runqemu`` replaces ``@MAC@`` with a predefined mac address.
:term:`QB_NFSROOTFS_EXTRA_OPT`
When using ``runqemu``, the :term:`QB_NFSROOTFS_EXTRA_OPT` variable
controls extra options to be appended to the NFS rootfs options in the
Linux kernel command-line.
For example::
QB_NFSROOTFS_EXTRA_OPT = "wsize=4096,rsize=4096"
:term:`QB_OPT_APPEND`
When using ``runqemu``, the :term:`QB_OPT_APPEND` variable controls
general options to append to QEMU when starting.
:term:`QB_RNG`
When using ``runqemu``, the :term:`QB_RNG` variable controls
pass-through for host random number generator, it can speedup boot
in system mode, where system is experiencing entropy starvation.
For example::
QB_RNG = "-object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-pci,rng=rng0"
:term:`QB_ROOTFS_EXTRA_OPT`
When using ``runqemu``, the :term:`QB_ROOTFS_EXTRA_OPT` variable controls
extra options to be appended to the rootfs device options.
:term:`QB_SERIAL_OPT`
When using ``runqemu``, the :term:`QB_SERIAL_OPT` variable controls the
serial port option.
For example::
QB_SERIAL_OPT = "-serial mon:stdio"
:term:`QB_SMP`
When using ``runqemu``, the :term:`QB_SMP` variable controls
amount of CPU cores made availalble inside the QEMU guest, each mapped to
a thread on the host.
For example::
QB_SMP = "-smp 8".
:term:`QB_TAP_OPT`
When using ``runqemu``, the :term:`QB_TAP_OPT` variable controls
the network option for "tap" mode.
For example::
QB_TAP_OPT = "-netdev tap,id=net0,ifname=@TAP@,script=no,downscript=no"
Note that ``runqemu`` will replace ``@TAP@`` with the tap interface in
use, such as ``tap0``, ``tap1``, etc.
:term:`RANLIB`
The minimal command and arguments to run :manpage:`ranlib <ranlib(1)>`.