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 section. 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 -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The acl option to the -vnc argument has been replaced
by the tls-authz and sasl-authz options.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.
Creating sound card devices and vnc without audiodev= property (since 4.2)¶
When not using the deprecated legacy audio config, each sound card
should specify an audiodev= property. Additionally, when using
vnc, you should specify an audiodev= propery if you plan to
transmit audio through the VNC protocol.
-mon ...,control=readline,pretty=on|off (since 4.1)¶
The pretty=on|off switch has no effect for HMP monitors, but is
silently ignored. Using the switch with HMP monitors will become an
error in the future.
-realtime (since 4.1)¶
The -realtime mlock=on|off argument has been replaced by the
-overcommit mem-lock=on|off argument.
-numa node,mem=size (since 4.1)¶
The parameter mem of -numa node is used to assign a part of
guest RAM to a NUMA node. But when using it, it’s impossible to manage specified
RAM chunk on the host side (like bind it to a host node, setting bind policy, …),
so guest end-ups with the fake NUMA configuration with suboptiomal performance.
However since 2014 there is an alternative way to assign RAM to a NUMA node
using parameter memdev, which does the same as mem and adds
means to actualy manage node RAM on the host side. Use parameter memdev
with memory-backend-ram backend as an replacement for parameter mem
to achieve the same fake NUMA effect or a properly configured
memory-backend-file backend to actually benefit from NUMA configuration.
In future new machine versions will not accept the option but it will still
work with old machine types. User can check QAPI schema to see if the legacy
option is supported by looking at MachineInfo::numa-mem-supported property.
-numa node (without memory specified) (since 4.1)¶
Splitting RAM by default between NUMA nodes has the same issues as mem
parameter described above with the difference that the role of the user plays
QEMU using implicit generic or board specific splitting rule.
Use memdev with memory-backend-ram backend or mem (if
it’s supported by used machine type) to define mapping explictly instead.
-mem-path fallback to RAM (since 4.1)¶
Currently if guest RAM allocation from file pointed by mem-path
fails, QEMU falls back to allocating from RAM, which might result
in unpredictable behavior since the backing file specified by the user
is ignored. In the future, users will be responsible for making sure
the backing storage specified with -mem-path can actually provide
the guest RAM configured with -m and QEMU will fail to start up if
RAM allocation is unsuccessful.
RISC-V -bios (since 4.1)¶
QEMU 4.1 introduced support for the -bios option in QEMU for RISC-V for the RISC-V virt machine and sifive_u machine.
QEMU 4.1 has no changes to the default behaviour to avoid breakages. This default will change in a future QEMU release, so please prepare now. All users of the virt or sifive_u machine must change their command line usage.
- QEMU 4.1 has three options, please migrate to one of these three:
-bios none- This is the current default behavior if no -bios optionis included. QEMU will not automatically load any firmware. It is up to the user to load all the images they need.
-bios default- In a future QEMU release this will become the defaultbehaviour if no -bios option is specified. This option will load the default OpenSBI firmware automatically. The firmware is included with the QEMU release and no user interaction is required. All a user needs to do is specify the kernel they want to boot with the -kernel option
-bios <file>- Tells QEMU to load the specified file as the firmwrae.
-tb-size option (since 5.0)¶
QEMU 5.0 introduced an alternative syntax to specify the size of the translation
block cache, -accel tcg,tb-size=. The new syntax deprecates the
previously available -tb-size option.
-show-cursor option (since 5.0)¶
- Use
-display sdl,show-cursor=onor -display gtk,show-cursor=oninstead.
QEMU Machine Protocol (QMP) commands¶
change (since 2.5.0)¶
Use blockdev-change-medium or change-vnc-password instead.
blockdev-open-tray, blockdev-close-tray argument device (since 2.8.0)¶
Use argument id instead.
eject argument device (since 2.8.0)¶
Use argument id instead.
blockdev-change-medium argument device (since 2.8.0)¶
Use argument id instead.
block_set_io_throttle argument device (since 2.8.0)¶
Use argument id instead.
migrate_set_downtime and migrate_set_speed (since 2.8.0)¶
Use migrate-set-parameters instead.
query-named-block-nodes result encryption_key_missing (since 2.10.0)¶
Always false.
query-block result inserted.encryption_key_missing (since 2.10.0)¶
Always false.
blockdev-add empty string argument backing (since 2.10.0)¶
Use argument value null instead.
migrate-set-cache-size and query-migrate-cache-size (since 2.11.0)¶
Use migrate-set-parameters and query-migrate-parameters instead.
block-commit arguments base and top (since 3.1.0)¶
Use arguments base-node and top-node instead.
object-add option props (since 5.0)¶
Specify the properties for the object as top-level arguments instead.
query-named-block-nodes and query-block result dirty-bitmaps[i].status (since 4.0)¶
The status field of the BlockDirtyInfo structure, returned by
these commands is deprecated. Two new boolean fields, recording and
busy effectively replace it.
query-block result field dirty-bitmaps (Since 4.2)¶
The dirty-bitmaps field of the BlockInfo structure, returned by
the query-block command is itself now deprecated. The dirty-bitmaps
field of the BlockDeviceInfo struct should be used instead, which is the
type of the inserted field in query-block replies, as well as the
type of array items in query-named-block-nodes.
Since the dirty-bitmaps field is optionally present in both the old and
new locations, clients must use introspection to learn where to anticipate
the field if/when it does appear in command output.
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.
chardev client socket with wait option (since 4.0)¶
Character devices creating sockets in client mode should not specify the ‘wait’ field, which is only applicable to sockets in server mode
Human Monitor Protocol (HMP) commands¶
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.
Guest Emulator ISAs¶
RISC-V ISA privledge specification version 1.09.1 (since 4.1)¶
The RISC-V ISA privledge specification version 1.09.1 has been deprecated. QEMU supports both the newer version 1.10.0 and the ratified version 1.11.0, these should be used instead of the 1.09.1 version.
System emulator CPUS¶
RISC-V ISA CPUs (since 4.1)¶
The RISC-V cpus with the ISA version in the CPU name have been depcreated. The
four CPUs are: rv32gcsu-v1.9.1, rv32gcsu-v1.10.0, rv64gcsu-v1.9.1 and
rv64gcsu-v1.10.0. Instead the version can be specified via the CPU priv_spec
option when using the rv32 or rv64 CPUs.
RISC-V ISA CPUs (since 4.1)¶
The RISC-V no MMU cpus have been depcreated. The two CPUs: rv32imacu-nommu and
rv64imacu-nommu should no longer be used. Instead the MMU status can be specified
via the CPU mmu option when using the rv32 or rv64 CPUs.
compat property of server class POWER CPUs (since 5.0)¶
The compat property used to set backwards compatibility modes for
the processor has been deprecated. The max-cpu-compat property of
the pseries machine type should be used instead.
KVM guest support on 32-bit Arm hosts (since 5.0)¶
The Linux kernel has dropped support for allowing 32-bit Arm systems to host KVM guests as of the 5.7 kernel. Accordingly, QEMU is deprecating its support for this configuration and will remove it in a future version. Running 32-bit guests on a 64-bit Arm host remains supported.
System emulator devices¶
ide-drive (since 4.2)¶
The ‘ide-drive’ device is deprecated. Users should use ‘ide-hd’ or ‘ide-cd’ as appropriate to get an IDE hard disk or CD-ROM as needed.
scsi-disk (since 4.2)¶
The ‘scsi-disk’ device is deprecated. Users should use ‘scsi-hd’ or ‘scsi-cd’ as appropriate to get a SCSI hard disk or CD-ROM as needed.
System emulator machines¶
mips r4k platform (since 5.0)¶
This machine type is very old and unmaintained. Users should use the malta
machine type instead.
pc-1.0, pc-1.1, pc-1.2 and pc-1.3 (since 5.0)¶
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.
spike_v1.9.1 and spike_v1.10 (since 4.1)¶
The version specific Spike machines have been deprecated in favour of the
generic spike machine. If you need to specify an older version of the RISC-V
spec you can use the -cpu rv64gcsu,priv_spec=v1.9.1 command line argument.
Device options¶
Emulated device options¶
-device virtio-blk,scsi=on|off (since 5.0.0)¶
The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 and later do not support it because the virtio-scsi device was introduced for full SCSI support. Use virtio-scsi instead when SCSI passthrough is required.
Note this also applies to -device virtio-blk-pci,scsi=on|off, which is an
alias.
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"}
Backwards compatibility¶
Runnability guarantee of CPU models (since 4.1.0)¶
Previous versions of QEMU never changed existing CPU models in ways that introduced additional host software or hardware requirements to the VM. This allowed management software to safely change the machine type of an existing VM without introducing new requirements (“runnability guarantee”). This prevented CPU models from being updated to include CPU vulnerability mitigations, leaving guests vulnerable in the default configuration.
The CPU model runnability guarantee won’t apply anymore to
existing CPU models. Management software that needs runnability
guarantees must resolve the CPU model aliases using te
alias-of field returned by the query-cpu-definitions QMP
command.
While those guarantees are kept, the return value of
query-cpu-definitions will have existing CPU model aliases
point to a version that doesn’t break runnability guarantees
(specifically, version 1 of those CPU models). In future QEMU
versions, aliases will point to newer CPU model versions
depending on the machine type, so management software must
resolve CPU model aliases before starting a virtual machine.
Recently removed features¶
What follows is a record of recently removed, formerly deprecated features that serves as a record for users who have encountered trouble after a recent upgrade.
QEMU Machine Protocol (QMP) commands¶
block-dirty-bitmap-add “autoload” parameter (since 4.2.0)¶
The “autoload” parameter has been ignored since 2.12.0. All bitmaps are automatically loaded from qcow2 images.
Human Monitor Protocol (HMP) commands¶
The hub_id parameter of hostfwd_add / hostfwd_remove (removed in 5.0)¶
The [hub_id name] parameter tuple of the ‘hostfwd_add’ and
‘hostfwd_remove’ HMP commands has been replaced by netdev_id.
Related binaries¶
qemu-nbd --partition (removed in 5.0.0)¶
The qemu-nbd --partition $digit code (also spelled -P)
could only handle MBR partitions, and never correctly handled logical
partitions beyond partition 5. Exporting a partition can still be
done by utilizing 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.file.driver=file,file.file.filename=file.qcow2