1 .. _Deprecated features:
6 In general features are intended to be supported indefinitely once
7 introduced into QEMU. In the event that a feature needs to be removed,
8 it will be listed in this section. The feature will remain functional for the
9 release in which it was deprecated and one further release. After these two
10 releases, the feature is liable to be removed. Deprecated features may also
11 generate warnings on the console when QEMU starts up, or if activated via a
12 monitor command, however, this is not a mandatory requirement.
14 Prior to the 2.10.0 release there was no official policy on how
15 long features would be deprecated prior to their removal, nor
16 any documented list of which features were deprecated. Thus
17 any features deprecated prior to 2.10.0 will be treated as if
18 they were first deprecated in the 2.10.0 release.
20 What follows is a list of all features currently marked as
23 System emulator command line arguments
24 --------------------------------------
26 Short-form boolean options (since 6.0)
27 ''''''''''''''''''''''''''''''''''''''
29 Boolean options such as ``share=on``/``share=off`` could be written
30 in short form as ``share`` and ``noshare``. This is now deprecated
31 and will cause a warning.
33 ``delay`` option for socket character devices (since 6.0)
34 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
36 The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on``
37 rather than ``delay=off``.
39 ``-smp`` ("parameter=0" SMP configurations) (since 6.2)
40 '''''''''''''''''''''''''''''''''''''''''''''''''''''''
42 Specified CPU topology parameters must be greater than zero.
44 In the SMP configuration, users should either provide a CPU topology
45 parameter with a reasonable value (greater than zero) or just omit it
46 and QEMU will compute the missing value.
48 However, historically it was implicitly allowed for users to provide
49 a parameter with zero value, which is meaningless and could also possibly
50 cause unexpected results in the -smp parsing. So support for this kind of
51 configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will
52 be removed in the near future, users have to ensure that all the topology
53 members described with -smp are greater than zero.
55 Plugin argument passing through ``arg=<string>`` (since 6.1)
56 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
58 Passing TCG plugins arguments through ``arg=`` is redundant is makes the
59 command-line less readable, especially when the argument itself consist of a
60 name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``.
61 Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated
62 as short-form boolean values, and passed to plugins as ``arg_name=on``.
63 However, short-form booleans are deprecated and full explicit ``arg_name=on``
66 ``-no-hpet`` (since 8.0)
67 ''''''''''''''''''''''''
69 The HPET setting has been turned into a machine property.
70 Use ``-machine hpet=off`` instead.
72 ``-no-acpi`` (since 8.0)
73 ''''''''''''''''''''''''
75 The ``-no-acpi`` setting has been turned into a machine property.
76 Use ``-machine acpi=off`` instead.
78 ``-async-teardown`` (since 8.1)
79 '''''''''''''''''''''''''''''''
81 Use ``-run-with async-teardown=on`` instead.
83 ``-chroot`` (since 8.1)
84 '''''''''''''''''''''''
86 Use ``-run-with chroot=dir`` instead.
88 ``-singlestep`` (since 8.1)
89 '''''''''''''''''''''''''''
91 The ``-singlestep`` option has been turned into an accelerator property,
92 and given a name that better reflects what it actually does.
93 Use ``-accel tcg,one-insn-per-tb=on`` instead.
95 User-mode emulator command line arguments
96 -----------------------------------------
98 ``-singlestep`` (since 8.1)
99 '''''''''''''''''''''''''''
101 The ``-singlestep`` option has been given a name that better reflects
102 what it actually does. For both linux-user and bsd-user, use the
103 new ``-one-insn-per-tb`` option instead.
105 QEMU Machine Protocol (QMP) commands
106 ------------------------------------
108 ``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8)
109 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
111 Use argument ``id`` instead.
113 ``eject`` argument ``device`` (since 2.8)
114 '''''''''''''''''''''''''''''''''''''''''
116 Use argument ``id`` instead.
118 ``blockdev-change-medium`` argument ``device`` (since 2.8)
119 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
121 Use argument ``id`` instead.
123 ``block_set_io_throttle`` argument ``device`` (since 2.8)
124 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
126 Use argument ``id`` instead.
128 ``blockdev-add`` empty string argument ``backing`` (since 2.10)
129 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
131 Use argument value ``null`` instead.
133 ``block-commit`` arguments ``base`` and ``top`` (since 3.1)
134 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
136 Use arguments ``base-node`` and ``top-node`` instead.
138 ``nbd-server-add`` and ``nbd-server-remove`` (since 5.2)
139 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
141 Use the more generic commands ``block-export-add`` and ``block-export-del``
142 instead. As part of this deprecation, where ``nbd-server-add`` used a
143 single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
145 ``query-qmp-schema`` return value member ``values`` (since 6.2)
146 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
148 Member ``values`` in return value elements with meta-type ``enum`` is
149 deprecated. Use ``members`` instead.
151 ``drive-backup`` (since 6.2)
152 ''''''''''''''''''''''''''''
154 Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
155 This change primarily separates the creation/opening process of the backup
156 target with explicit, separate steps. ``blockdev-backup`` uses mostly the
157 same arguments as ``drive-backup``, except the ``format`` and ``mode``
158 options are removed in favor of using explicit ``blockdev-create`` and
159 ``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
162 Incorrectly typed ``device_add`` arguments (since 6.2)
163 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
165 Due to shortcomings in the internal implementation of ``device_add``, QEMU
166 incorrectly accepts certain invalid arguments: Any object or list arguments are
167 silently ignored. Other argument types are not checked, but an implicit
168 conversion happens, so that e.g. string values can be assigned to integer
169 device properties or vice versa.
171 This is a bug in QEMU that will be fixed in the future so that previously
172 accepted incorrect commands will return an error. Users should make sure that
173 all arguments passed to ``device_add`` are consistent with the documented
176 ``StatusInfo`` member ``singlestep`` (since 8.1)
177 ''''''''''''''''''''''''''''''''''''''''''''''''
179 The ``singlestep`` member of the ``StatusInfo`` returned from the
180 ``query-status`` command is deprecated. This member has a confusing
181 name and it never did what the documentation claimed or what its name
182 suggests. We do not believe that anybody is actually using the
183 information provided in this member.
185 The information it reports is whether the TCG JIT is in "one
186 instruction per translated block" mode (which can be set on the
187 command line or via the HMP, but not via QMP). The information remains
188 available via the HMP 'info jit' command.
190 QEMU Machine Protocol (QMP) events
191 ----------------------------------
193 ``MEM_UNPLUG_ERROR`` (since 6.2)
194 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
196 Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.
198 ``vcpu`` trace events (since 8.1)
199 '''''''''''''''''''''''''''''''''
201 The ability to instrument QEMU helper functions with vCPU-aware trace
202 points was removed in 7.0. However QMP still exposed the vcpu
203 parameter. This argument has now been deprecated and the remaining
204 remaining trace points that used it are selected just by name.
206 Human Monitor Protocol (HMP) commands
207 -------------------------------------
209 ``singlestep`` (since 8.1)
210 ''''''''''''''''''''''''''
212 The ``singlestep`` command has been replaced by the ``one-insn-per-tb``
213 command, which has the same behaviour but a less misleading name.
221 As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
222 MIPS moved out of support making it hard to maintain our
223 cross-compilation CI tests of the architecture. As we no longer have
224 CI coverage support may bitrot away before the deprecation process
225 completes. The little endian variants of MIPS (both 32 and 64 bit) are
226 still a supported host architecture.
228 System emulation on 32-bit x86 hosts (since 8.0)
229 ''''''''''''''''''''''''''''''''''''''''''''''''
231 Support for 32-bit x86 host deployments is increasingly uncommon in mainstream
232 OS distributions given the widespread availability of 64-bit x86 hardware.
233 The QEMU project no longer considers 32-bit x86 support for system emulation to
234 be an effective use of its limited resources, and thus intends to discontinue
235 it. Since all recent x86 hardware from the past >10 years is capable of the
236 64-bit x86 extensions, a corresponding 64-bit OS should be used instead.
239 System emulator machines
240 ------------------------
242 Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
243 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
245 The ``dtb-kaslr-seed`` property on the ``virt`` board has been
246 deprecated; use the new name ``dtb-randomness`` instead. The new name
247 better reflects the way this property affects all random data within
248 the device tree blob, not just the ``kaslr-seed`` node.
253 Using non-persistent backing file with pmem=on (since 6.1)
254 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
256 This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
257 device. However enabling ``memory-backend-file.pmem`` option, when backing file
258 is (a) not DAX capable or (b) not on a filesystem that support direct mapping
259 of persistent memory, is not safe and may lead to data loss or corruption in case
263 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
264 (without persistence guaranties) with backing file on non DAX storage
265 - move backing file to NVDIMM storage and keep ``pmem=on``
266 (to have NVDIMM with persistence guaranties).
271 Emulated device options
272 '''''''''''''''''''''''
274 ``-device virtio-blk,scsi=on|off`` (since 5.0)
275 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
277 The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0
278 and later do not support it because the virtio-scsi device was introduced for
279 full SCSI support. Use virtio-scsi instead when SCSI passthrough is required.
281 Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
284 ``-device nvme-ns,eui64-default=on|off`` (since 7.1)
285 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
287 In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
288 identifier that is not globally unique. If an EUI-64 identifier is required, the
289 user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``.
291 ``-device nvme,use-intel-id=on|off`` (since 7.1)
292 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
294 The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
295 from Intel that was not properly allocated. Since version 5.2, the controller
296 has used a properly allocated identifier. Deprecate the ``use-intel-id``
297 machine compatibility parameter.
299 ``-device cxl-type3,memdev=xxxx`` (since 8.0)
300 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
302 The ``cxl-type3`` device initially only used a single memory backend. With
303 the addition of volatile memory support, it is now necessary to distinguish
304 between persistent and volatile memory backends. As such, memdev is deprecated
305 in favor of persistent-memdev.
307 ``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1)
308 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
310 The 9p ``proxy`` filesystem backend driver has been deprecated and will be
311 removed (along with its proxy helper daemon) in a future version of QEMU. Please
312 use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem
313 backend, or alternatively consider deploying virtiofsd instead.
315 The 9p ``proxy`` backend was originally developed as an alternative to the 9p
316 ``local`` backend. The idea was to enhance security by dispatching actual low
317 level filesystem operations from 9p server (QEMU process) over to a separate
318 process (the virtfs-proxy-helper binary). However this alternative never gained
319 momentum. The proxy backend is much slower than the local backend, hasn't seen
320 any development in years, and showed to be less secure, especially due to the
321 fact that its helper daemon must be run as root, whereas with the local backend
322 QEMU is typically run as unprivileged user and allows to tighten behaviour by
323 mapping permissions et al by using its 'mapped' security model option.
325 Nowadays it would make sense to reimplement the ``proxy`` backend by using
326 QEMU's ``vhost`` feature, which would eliminate the high latency costs under
327 which the 9p ``proxy`` backend currently suffers. However as of to date nobody
328 has indicated plans for such kind of reimplementation unfortunately.
330 RISC-V 'any' CPU type ``-cpu any`` (since 8.2)
331 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
333 The 'any' CPU type was introduced back in 2018 and has been around since the
334 initial RISC-V QEMU port. Its usage has always been unclear: users don't know
335 what to expect from a CPU called 'any', and in fact the CPU does not do anything
336 special that isn't already done by the default CPUs rv32/rv64.
338 After the introduction of the 'max' CPU type, RISC-V now has a good coverage
339 of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete
340 CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any'
341 CPU type starting in 8.2.
343 RISC-V CPU properties which start with capital 'Z' (since 8.2)
344 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
346 All RISC-V CPU properties which start with capital 'Z' are being deprecated
347 starting in 8.2. The reason is that they were wrongly added with capital 'Z'
348 in the past. CPU properties were later added with lower-case names, which
349 is the format we want to use from now on.
351 Users which try to use these deprecated properties will receive a warning
352 recommending to switch to their stable counterparts:
354 - "Zifencei" should be replaced with "zifencei"
355 - "Zicsr" should be replaced with "zicsr"
356 - "Zihintntl" should be replaced with "zihintntl"
357 - "Zihintpause" should be replaced with "zihintpause"
358 - "Zawrs" should be replaced with "zawrs"
359 - "Zfa" should be replaced with "zfa"
360 - "Zfh" should be replaced with "zfh"
361 - "Zfhmin" should be replaced with "zfhmin"
362 - "Zve32f" should be replaced with "zve32f"
363 - "Zve64f" should be replaced with "zve64f"
364 - "Zve64d" should be replaced with "zve64d"
369 ``"backing": ""`` (since 2.12)
370 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
372 In order to prevent QEMU from automatically opening an image's backing
373 chain, use ``"backing": null`` instead.
375 ``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1)
376 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
378 Options for ``rbd`` should be specified according to its runtime options,
379 like other block drivers. Legacy parsing of keyvalue pair encoded
380 filenames is useful to open images with the old format for backing files;
381 These image files should be updated to use the current format.
383 Example of legacy encoding::
385 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}
387 The above, converted to the current supported format::
389 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
391 ``iscsi,password=xxx`` (since 8.0)
392 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
394 Specifying the iSCSI password in plain text on the command line using the
395 ``password`` option is insecure. The ``password-secret`` option should be
396 used instead, to refer to a ``--object secret...`` instance that provides
397 a password via a file, or encrypted.
399 Backwards compatibility
400 -----------------------
402 Runnability guarantee of CPU models (since 4.1)
403 '''''''''''''''''''''''''''''''''''''''''''''''
405 Previous versions of QEMU never changed existing CPU models in
406 ways that introduced additional host software or hardware
407 requirements to the VM. This allowed management software to
408 safely change the machine type of an existing VM without
409 introducing new requirements ("runnability guarantee"). This
410 prevented CPU models from being updated to include CPU
411 vulnerability mitigations, leaving guests vulnerable in the
412 default configuration.
414 The CPU model runnability guarantee won't apply anymore to
415 existing CPU models. Management software that needs runnability
416 guarantees must resolve the CPU model aliases using the
417 ``alias-of`` field returned by the ``query-cpu-definitions`` QMP
420 While those guarantees are kept, the return value of
421 ``query-cpu-definitions`` will have existing CPU model aliases
422 point to a version that doesn't break runnability guarantees
423 (specifically, version 1 of those CPU models). In future QEMU
424 versions, aliases will point to newer CPU model versions
425 depending on the machine type, so management software must
426 resolve CPU model aliases before starting a virtual machine.
431 ``--blacklist`` command line option (since 7.2)
432 '''''''''''''''''''''''''''''''''''''''''''''''
434 ``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
435 wording for what this option does). The short form ``-b`` still stays
436 the same and thus is the preferred way for scripts that should run with
437 both, older and future versions of QEMU.
439 ``blacklist`` config file option (since 7.2)
440 ''''''''''''''''''''''''''''''''''''''''''''
442 The ``blacklist`` config file option has been renamed to ``block-rpcs``
443 (to be in sync with the renaming of the corresponding command line
449 ``skipped`` MigrationStats field (since 8.1)
450 ''''''''''''''''''''''''''''''''''''''''''''
452 ``skipped`` field in Migration stats has been deprecated. It hasn't
453 been used for more than 10 years.