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 QEMU Machine Protocol (QMP) commands
67 ------------------------------------
69 ``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8)
70 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
72 Use argument ``id`` instead.
74 ``eject`` argument ``device`` (since 2.8)
75 '''''''''''''''''''''''''''''''''''''''''
77 Use argument ``id`` instead.
79 ``blockdev-change-medium`` argument ``device`` (since 2.8)
80 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
82 Use argument ``id`` instead.
84 ``block_set_io_throttle`` argument ``device`` (since 2.8)
85 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
87 Use argument ``id`` instead.
89 ``blockdev-add`` empty string argument ``backing`` (since 2.10)
90 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
92 Use argument value ``null`` instead.
94 ``block-commit`` arguments ``base`` and ``top`` (since 3.1)
95 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
97 Use arguments ``base-node`` and ``top-node`` instead.
99 ``nbd-server-add`` and ``nbd-server-remove`` (since 5.2)
100 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
102 Use the more generic commands ``block-export-add`` and ``block-export-del``
103 instead. As part of this deprecation, where ``nbd-server-add`` used a
104 single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
106 ``query-qmp-schema`` return value member ``values`` (since 6.2)
107 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
109 Member ``values`` in return value elements with meta-type ``enum`` is
110 deprecated. Use ``members`` instead.
112 ``drive-backup`` (since 6.2)
113 ''''''''''''''''''''''''''''
115 Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
116 This change primarily separates the creation/opening process of the backup
117 target with explicit, separate steps. ``blockdev-backup`` uses mostly the
118 same arguments as ``drive-backup``, except the ``format`` and ``mode``
119 options are removed in favor of using explicit ``blockdev-create`` and
120 ``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
123 Incorrectly typed ``device_add`` arguments (since 6.2)
124 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
126 Due to shortcomings in the internal implementation of ``device_add``, QEMU
127 incorrectly accepts certain invalid arguments: Any object or list arguments are
128 silently ignored. Other argument types are not checked, but an implicit
129 conversion happens, so that e.g. string values can be assigned to integer
130 device properties or vice versa.
132 This is a bug in QEMU that will be fixed in the future so that previously
133 accepted incorrect commands will return an error. Users should make sure that
134 all arguments passed to ``device_add`` are consistent with the documented
137 QEMU Machine Protocol (QMP) events
138 ----------------------------------
140 ``MEM_UNPLUG_ERROR`` (since 6.2)
141 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
143 Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.
145 ``vcpu`` trace events (since 8.1)
146 '''''''''''''''''''''''''''''''''
148 The ability to instrument QEMU helper functions with vCPU-aware trace
149 points was removed in 7.0. However QMP still exposed the vcpu
150 parameter. This argument has now been deprecated and the remaining
151 remaining trace points that used it are selected just by name.
159 As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
160 MIPS moved out of support making it hard to maintain our
161 cross-compilation CI tests of the architecture. As we no longer have
162 CI coverage support may bitrot away before the deprecation process
163 completes. The little endian variants of MIPS (both 32 and 64 bit) are
164 still a supported host architecture.
166 System emulation on 32-bit x86 hosts (since 8.0)
167 ''''''''''''''''''''''''''''''''''''''''''''''''
169 Support for 32-bit x86 host deployments is increasingly uncommon in mainstream
170 OS distributions given the widespread availability of 64-bit x86 hardware.
171 The QEMU project no longer considers 32-bit x86 support for system emulation to
172 be an effective use of its limited resources, and thus intends to discontinue
173 it. Since all recent x86 hardware from the past >10 years is capable of the
174 64-bit x86 extensions, a corresponding 64-bit OS should be used instead.
180 Nios II CPU (since 8.2)
181 '''''''''''''''''''''''
183 The Nios II architecture is orphan. The ``nios2`` guest CPU support is
184 deprecated and will be removed in a future version of QEMU.
187 System emulator machines
188 ------------------------
190 Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
191 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
193 The ``dtb-kaslr-seed`` property on the ``virt`` board has been
194 deprecated; use the new name ``dtb-randomness`` instead. The new name
195 better reflects the way this property affects all random data within
196 the device tree blob, not just the ``kaslr-seed`` node.
198 ``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2)
199 '''''''''''''''''''''''''''''''''''''''''''''''''''''
201 These old machine types are quite neglected nowadays and thus might have
202 various pitfalls with regards to live migration. Use a newer machine type
205 Nios II ``10m50-ghrd`` and ``nios2-generic-nommu`` machines (since 8.2)
206 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
208 The Nios II architecture is orphan.
213 The machine is no longer in existence and has been long unmaintained
214 in QEMU. This also holds for the TC51828 16MiB flash that it uses.
219 Using non-persistent backing file with pmem=on (since 6.1)
220 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
222 This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
223 device. However enabling ``memory-backend-file.pmem`` option, when backing file
224 is (a) not DAX capable or (b) not on a filesystem that support direct mapping
225 of persistent memory, is not safe and may lead to data loss or corruption in case
229 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
230 (without persistence guaranties) with backing file on non DAX storage
231 - move backing file to NVDIMM storage and keep ``pmem=on``
232 (to have NVDIMM with persistence guaranties).
237 Emulated device options
238 '''''''''''''''''''''''
240 ``-device virtio-blk,scsi=on|off`` (since 5.0)
241 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
243 The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0
244 and later do not support it because the virtio-scsi device was introduced for
245 full SCSI support. Use virtio-scsi instead when SCSI passthrough is required.
247 Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
250 ``-device nvme-ns,eui64-default=on|off`` (since 7.1)
251 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
253 In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
254 identifier that is not globally unique. If an EUI-64 identifier is required, the
255 user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``.
257 ``-device nvme,use-intel-id=on|off`` (since 7.1)
258 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
260 The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
261 from Intel that was not properly allocated. Since version 5.2, the controller
262 has used a properly allocated identifier. Deprecate the ``use-intel-id``
263 machine compatibility parameter.
265 ``-device cxl-type3,memdev=xxxx`` (since 8.0)
266 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
268 The ``cxl-type3`` device initially only used a single memory backend. With
269 the addition of volatile memory support, it is now necessary to distinguish
270 between persistent and volatile memory backends. As such, memdev is deprecated
271 in favor of persistent-memdev.
273 ``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1)
274 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
276 The 9p ``proxy`` filesystem backend driver has been deprecated and will be
277 removed (along with its proxy helper daemon) in a future version of QEMU. Please
278 use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem
279 backend, or alternatively consider deploying virtiofsd instead.
281 The 9p ``proxy`` backend was originally developed as an alternative to the 9p
282 ``local`` backend. The idea was to enhance security by dispatching actual low
283 level filesystem operations from 9p server (QEMU process) over to a separate
284 process (the virtfs-proxy-helper binary). However this alternative never gained
285 momentum. The proxy backend is much slower than the local backend, hasn't seen
286 any development in years, and showed to be less secure, especially due to the
287 fact that its helper daemon must be run as root, whereas with the local backend
288 QEMU is typically run as unprivileged user and allows to tighten behaviour by
289 mapping permissions et al by using its 'mapped' security model option.
291 Nowadays it would make sense to reimplement the ``proxy`` backend by using
292 QEMU's ``vhost`` feature, which would eliminate the high latency costs under
293 which the 9p ``proxy`` backend currently suffers. However as of to date nobody
294 has indicated plans for such kind of reimplementation unfortunately.
296 RISC-V 'any' CPU type ``-cpu any`` (since 8.2)
297 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
299 The 'any' CPU type was introduced back in 2018 and has been around since the
300 initial RISC-V QEMU port. Its usage has always been unclear: users don't know
301 what to expect from a CPU called 'any', and in fact the CPU does not do anything
302 special that isn't already done by the default CPUs rv32/rv64.
304 After the introduction of the 'max' CPU type, RISC-V now has a good coverage
305 of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete
306 CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any'
307 CPU type starting in 8.2.
309 RISC-V CPU properties which start with capital 'Z' (since 8.2)
310 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
312 All RISC-V CPU properties which start with capital 'Z' are being deprecated
313 starting in 8.2. The reason is that they were wrongly added with capital 'Z'
314 in the past. CPU properties were later added with lower-case names, which
315 is the format we want to use from now on.
317 Users which try to use these deprecated properties will receive a warning
318 recommending to switch to their stable counterparts:
320 - "Zifencei" should be replaced with "zifencei"
321 - "Zicsr" should be replaced with "zicsr"
322 - "Zihintntl" should be replaced with "zihintntl"
323 - "Zihintpause" should be replaced with "zihintpause"
324 - "Zawrs" should be replaced with "zawrs"
325 - "Zfa" should be replaced with "zfa"
326 - "Zfh" should be replaced with "zfh"
327 - "Zfhmin" should be replaced with "zfhmin"
328 - "Zve32f" should be replaced with "zve32f"
329 - "Zve64f" should be replaced with "zve64f"
330 - "Zve64d" should be replaced with "zve64d"
332 ``-device pvrdma`` and the rdma subsystem (since 8.2)
333 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
335 The pvrdma device and the whole rdma subsystem are in a bad shape and
336 without active maintenance. The QEMU project intends to remove this
337 device and subsystem from the code base in a future release without
338 replacement unless somebody steps up and improves the situation.
344 ``"backing": ""`` (since 2.12)
345 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
347 In order to prevent QEMU from automatically opening an image's backing
348 chain, use ``"backing": null`` instead.
350 ``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1)
351 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
353 Options for ``rbd`` should be specified according to its runtime options,
354 like other block drivers. Legacy parsing of keyvalue pair encoded
355 filenames is useful to open images with the old format for backing files;
356 These image files should be updated to use the current format.
358 Example of legacy encoding::
360 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}
362 The above, converted to the current supported format::
364 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
366 ``iscsi,password=xxx`` (since 8.0)
367 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
369 Specifying the iSCSI password in plain text on the command line using the
370 ``password`` option is insecure. The ``password-secret`` option should be
371 used instead, to refer to a ``--object secret...`` instance that provides
372 a password via a file, or encrypted.
374 CPU device properties
375 '''''''''''''''''''''
377 ``pmu-num=n`` on RISC-V CPUs (since 8.2)
378 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
380 In order to support more flexible counter configurations this has been replaced
381 by a ``pmu-mask`` property. If set of counters is continuous then the mask can
382 be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits
386 Backwards compatibility
387 -----------------------
389 Runnability guarantee of CPU models (since 4.1)
390 '''''''''''''''''''''''''''''''''''''''''''''''
392 Previous versions of QEMU never changed existing CPU models in
393 ways that introduced additional host software or hardware
394 requirements to the VM. This allowed management software to
395 safely change the machine type of an existing VM without
396 introducing new requirements ("runnability guarantee"). This
397 prevented CPU models from being updated to include CPU
398 vulnerability mitigations, leaving guests vulnerable in the
399 default configuration.
401 The CPU model runnability guarantee won't apply anymore to
402 existing CPU models. Management software that needs runnability
403 guarantees must resolve the CPU model aliases using the
404 ``alias-of`` field returned by the ``query-cpu-definitions`` QMP
407 While those guarantees are kept, the return value of
408 ``query-cpu-definitions`` will have existing CPU model aliases
409 point to a version that doesn't break runnability guarantees
410 (specifically, version 1 of those CPU models). In future QEMU
411 versions, aliases will point to newer CPU model versions
412 depending on the machine type, so management software must
413 resolve CPU model aliases before starting a virtual machine.
418 ``--blacklist`` command line option (since 7.2)
419 '''''''''''''''''''''''''''''''''''''''''''''''
421 ``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
422 wording for what this option does). The short form ``-b`` still stays
423 the same and thus is the preferred way for scripts that should run with
424 both, older and future versions of QEMU.
426 ``blacklist`` config file option (since 7.2)
427 ''''''''''''''''''''''''''''''''''''''''''''
429 The ``blacklist`` config file option has been renamed to ``block-rpcs``
430 (to be in sync with the renaming of the corresponding command line
436 ``skipped`` MigrationStats field (since 8.1)
437 ''''''''''''''''''''''''''''''''''''''''''''
439 ``skipped`` field in Migration stats has been deprecated. It hasn't
440 been used for more than 10 years.
442 ``inc`` migrate command option (since 8.2)
443 ''''''''''''''''''''''''''''''''''''''''''
445 Use blockdev-mirror with NBD instead.
447 As an intermediate step the ``inc`` functionality can be achieved by
448 setting the ``block-incremental`` migration parameter to ``true``.
449 But this parameter is also deprecated.
451 ``blk`` migrate command option (since 8.2)
452 ''''''''''''''''''''''''''''''''''''''''''
454 Use blockdev-mirror with NBD instead.
456 As an intermediate step the ``blk`` functionality can be achieved by
457 setting the ``block`` migration capability to ``true``. But this
458 capability is also deprecated.
460 block migration (since 8.2)
461 '''''''''''''''''''''''''''
463 Block migration is too inflexible. It needs to migrate all block
466 Please see "QMP invocation for live storage migration with
467 ``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst
468 for a detailed explanation.
470 old compression method (since 8.2)
471 ''''''''''''''''''''''''''''''''''
473 Compression method fails too much. Too many races. We are going to
474 remove it if nobody fixes it. For starters, migration-test
475 compression tests are disabled because they fail randomly. If you need
476 compression, use multifd compression methods.