Deprecated features
*******************

In general features are intended to be supported indefinitely once introduced into QEMU. In the event that a feature needs to be removed, it will be listed in this appendix. The feature will remain functional for 2 releases prior to actual removal. Deprecated features may also generate warnings on the console when QEMU starts up, or if activated via a monitor command, however, this is not a mandatory requirement.

Prior to the 2.10.0 release there was no official policy on how long features would be deprecated prior to their removal, nor any documented list of which features were deprecated. Thus any features deprecated prior to 2.10.0 will be treated as if they were first deprecated in the 2.10.0 release.

What follows is a list of all features currently marked as deprecated.

System emulator command line arguments
======================================

-machine enforce-config-section=on|off (since 3.1)
--------------------------------------------------

The enforce-config-section parameter is replaced by the -global migration.send-configuration=ON|OFF option.

-no-kvm (since 1.3.0)
---------------------

The ``-no-kvm'' argument is now a synonym for setting ``-machine accel=tcg''.

-usbdevice (since 2.10.0)
-------------------------

The ``-usbdevice DEV'' argument is now a synonym for setting the ``-device usb-DEV'' argument instead. The deprecated syntax would automatically enable USB support on the machine type. If using the new syntax, USB support must be explicitly enabled via the ``-machine usb=on'' argument.

-drive file=json:{...{'driver':'file'}} (since 3.0)
---------------------------------------------------

The 'file' driver for drives is no longer appropriate for character or host devices and will only accept regular files (S_IFREG). The correct driver for these file types is 'host_cdrom' or 'host_device' as appropriate.

-net ...,name=NAME (since 3.1)
------------------------------

The name parameter of the -net option is a synonym for the id parameter, which should now be used instead.

-smp (invalid topologies) (since 3.1)
-------------------------------------

CPU topology properties should describe whole machine topology including possible CPUs.

However, historically it was possible to start QEMU with an incorrect topology where N <= SOCKETS * CORES * THREADS < MAXCPUS, which could lead to an incorrect topology enumeration by the guest. Support for invalid topologies will be removed, the user must ensure topologies described with -smp include all possible cpus, i.e. SOCKETS * CORES * THREADS = MAXCPUS.

-vnc acl (since 4.0.0)
----------------------

The acl option to the -vnc argument has been replaced by the tls-authz and sasl-authz options.

QEMU_AUDIO_ environment variables and -audio-help (since 4.0)
-------------------------------------------------------------

The ``-audiodev'' argument is now the preferred way to specify audio backend settings instead of environment variables.  To ease migration to the new format, the ``-audiodev-help'' option can be used to convert the current values of the environment variables to ``-audiodev'' options.

QEMU Machine Protocol (QMP) commands
====================================

block-dirty-bitmap-add "autoload" parameter (since 2.12.0)
----------------------------------------------------------

"autoload" parameter is now ignored. All bitmaps are automatically loaded from qcow2 images.

query-block result field dirty-bitmaps[i].status (since 4.0)
------------------------------------------------------------

The ``status'' field of the ``BlockDirtyInfo'' structure, returned by the query-block command is deprecated. Two new boolean fields, ``recording'' and ``busy'' effectively replace it.

query-cpus (since 2.12.0)
-------------------------

The ``query-cpus'' command is replaced by the ``query-cpus-fast'' command.

query-cpus-fast "arch" output member (since 3.0.0)
--------------------------------------------------

The ``arch'' output member of the ``query-cpus-fast'' command is replaced by the ``target'' output member.

cpu-add (since 4.0)
-------------------

Use ``device_add'' for hotplugging vCPUs instead of ``cpu-add''.  See documentation of ``query-hotpluggable-cpus'' for additional details.

query-events (since 4.0)
------------------------

The ``query-events'' command has been superseded by the more powerful and accurate ``query-qmp-schema'' command.

Human Monitor Protocol (HMP) commands
=====================================

The hub_id parameter of 'hostfwd_add' / 'hostfwd_remove' (since 3.1)
--------------------------------------------------------------------

The [hub_id name] parameter tuple of the 'hostfwd_add' and 'hostfwd_remove' HMP commands has been replaced by netdev_id.

cpu-add (since 4.0)
-------------------

Use ``device_add'' for hotplugging vCPUs instead of ``cpu-add''.  See documentation of ``query-hotpluggable-cpus'' for additional details.

acl_show, acl_reset, acl_policy, acl_add, acl_remove (since 4.0.0)
------------------------------------------------------------------

The ``acl_show'', ``acl_reset'', ``acl_policy'', ``acl_add'', and ``acl_remove'' commands are deprecated with no replacement. Authorization for VNC should be performed using the pluggable QAuthZ objects.

System emulator devices
=======================

bluetooth (since 3.1)
---------------------

The bluetooth subsystem is unmaintained since many years and likely bitrotten quite a bit. It will be removed without replacement unless some users speaks up at the qemu-devel@nongnu.org mailing list with information about their usecases.

System emulator machines
========================

pc-0.12, pc-0.13, pc-0.14 and pc-0.15 (since 4.0)
-------------------------------------------------

These machine types are very old and likely can not be used for live migration from old QEMU versions anymore. A newer machine type should be used instead.

prep (PowerPC) (since 3.1)
--------------------------

This machine type uses an unmaintained firmware, broken in lots of ways, and unable to start post-2004 operating systems. 40p machine type should be used instead.

Device options
==============

Block device options
--------------------

"backing": "" (since 2.12.0)
............................

In order to prevent QEMU from automatically opening an image's backing chain, use ``"backing": null'' instead.

rbd keyvalue pair encoded filenames: "" (since 3.1.0)
.....................................................

Options for ``rbd'' should be specified according to its runtime options, like other block drivers.  Legacy parsing of keyvalue pair encoded filenames is useful to open images with the old format for backing files; These image files should be updated to use the current format.

Example of legacy encoding:

json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}

The above, converted to the current supported format:

json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}

Related binaries
================

qemu-nbd --partition (since 4.0.0)
----------------------------------

The ``qemu-nbd --partition $digit'' code (also spelled -P) can only handle MBR partitions, and has never correctly handled logical partitions beyond partition 5.  If you know the offset and length of the partition (perhaps by using sfdisk within the guest), you can achieve the effect of exporting just that subset of the disk by use of the --image-opts option with a raw blockdev using the offset and size parameters layered on top of any other existing blockdev. For example, if partition 1 is 100MiB long starting at 1MiB, the old command:

qemu-nbd -t -P 1 -f qcow2 file.qcow2

can be rewritten as:

qemu-nbd -t --image-opts driver=raw,offset=1M,size=100M,file.driver=qcow2,file.backing.driver=file,file.backing.filename=file.qcow2

Alternatively, the nbdkit project provides a more powerful partition filter on top of its nbd plugin, which can be used to select an arbitrary MBR or GPT partition on top of any other full-image NBD export.  Using this to rewrite the above example results in:

qemu-nbd -t -k /tmp/sock -f qcow2 file.qcow2 & nbdkit -f --filter=partition nbd socket=/tmp/sock partition=1

Note that if you are exposing the export via /dev/nbd0, it is easier to just export the entire image and then mount only /dev/nbd0p1 than it is to reinvoke qemu-nbd -c /dev/nbd0 limited to just a subset of the image.