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.
242 Nios II CPU (since 8.2)
243 '''''''''''''''''''''''
245 The Nios II architecture is orphan. The ``nios2`` guest CPU support is
246 deprecated and will be removed in a future version of QEMU.
249 System emulator machines
250 ------------------------
252 Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
253 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
255 The ``dtb-kaslr-seed`` property on the ``virt`` board has been
256 deprecated; use the new name ``dtb-randomness`` instead. The new name
257 better reflects the way this property affects all random data within
258 the device tree blob, not just the ``kaslr-seed`` node.
260 ``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2)
261 '''''''''''''''''''''''''''''''''''''''''''''''''''''
263 These old machine types are quite neglected nowadays and thus might have
264 various pitfalls with regards to live migration. Use a newer machine type
267 Nios II ``10m50-ghrd`` and ``nios2-generic-nommu`` machines (since 8.2)
268 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
270 The Nios II architecture is orphan.
275 The machine is no longer in existence and has been long unmaintained
276 in QEMU. This also holds for the TC51828 16MiB flash that it uses.
281 Using non-persistent backing file with pmem=on (since 6.1)
282 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
284 This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
285 device. However enabling ``memory-backend-file.pmem`` option, when backing file
286 is (a) not DAX capable or (b) not on a filesystem that support direct mapping
287 of persistent memory, is not safe and may lead to data loss or corruption in case
291 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
292 (without persistence guaranties) with backing file on non DAX storage
293 - move backing file to NVDIMM storage and keep ``pmem=on``
294 (to have NVDIMM with persistence guaranties).
299 Emulated device options
300 '''''''''''''''''''''''
302 ``-device virtio-blk,scsi=on|off`` (since 5.0)
303 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
305 The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0
306 and later do not support it because the virtio-scsi device was introduced for
307 full SCSI support. Use virtio-scsi instead when SCSI passthrough is required.
309 Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
312 ``-device nvme-ns,eui64-default=on|off`` (since 7.1)
313 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
315 In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
316 identifier that is not globally unique. If an EUI-64 identifier is required, the
317 user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``.
319 ``-device nvme,use-intel-id=on|off`` (since 7.1)
320 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
322 The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
323 from Intel that was not properly allocated. Since version 5.2, the controller
324 has used a properly allocated identifier. Deprecate the ``use-intel-id``
325 machine compatibility parameter.
327 ``-device cxl-type3,memdev=xxxx`` (since 8.0)
328 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
330 The ``cxl-type3`` device initially only used a single memory backend. With
331 the addition of volatile memory support, it is now necessary to distinguish
332 between persistent and volatile memory backends. As such, memdev is deprecated
333 in favor of persistent-memdev.
335 ``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1)
336 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
338 The 9p ``proxy`` filesystem backend driver has been deprecated and will be
339 removed (along with its proxy helper daemon) in a future version of QEMU. Please
340 use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem
341 backend, or alternatively consider deploying virtiofsd instead.
343 The 9p ``proxy`` backend was originally developed as an alternative to the 9p
344 ``local`` backend. The idea was to enhance security by dispatching actual low
345 level filesystem operations from 9p server (QEMU process) over to a separate
346 process (the virtfs-proxy-helper binary). However this alternative never gained
347 momentum. The proxy backend is much slower than the local backend, hasn't seen
348 any development in years, and showed to be less secure, especially due to the
349 fact that its helper daemon must be run as root, whereas with the local backend
350 QEMU is typically run as unprivileged user and allows to tighten behaviour by
351 mapping permissions et al by using its 'mapped' security model option.
353 Nowadays it would make sense to reimplement the ``proxy`` backend by using
354 QEMU's ``vhost`` feature, which would eliminate the high latency costs under
355 which the 9p ``proxy`` backend currently suffers. However as of to date nobody
356 has indicated plans for such kind of reimplementation unfortunately.
358 RISC-V 'any' CPU type ``-cpu any`` (since 8.2)
359 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
361 The 'any' CPU type was introduced back in 2018 and has been around since the
362 initial RISC-V QEMU port. Its usage has always been unclear: users don't know
363 what to expect from a CPU called 'any', and in fact the CPU does not do anything
364 special that isn't already done by the default CPUs rv32/rv64.
366 After the introduction of the 'max' CPU type, RISC-V now has a good coverage
367 of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete
368 CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any'
369 CPU type starting in 8.2.
371 RISC-V CPU properties which start with capital 'Z' (since 8.2)
372 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
374 All RISC-V CPU properties which start with capital 'Z' are being deprecated
375 starting in 8.2. The reason is that they were wrongly added with capital 'Z'
376 in the past. CPU properties were later added with lower-case names, which
377 is the format we want to use from now on.
379 Users which try to use these deprecated properties will receive a warning
380 recommending to switch to their stable counterparts:
382 - "Zifencei" should be replaced with "zifencei"
383 - "Zicsr" should be replaced with "zicsr"
384 - "Zihintntl" should be replaced with "zihintntl"
385 - "Zihintpause" should be replaced with "zihintpause"
386 - "Zawrs" should be replaced with "zawrs"
387 - "Zfa" should be replaced with "zfa"
388 - "Zfh" should be replaced with "zfh"
389 - "Zfhmin" should be replaced with "zfhmin"
390 - "Zve32f" should be replaced with "zve32f"
391 - "Zve64f" should be replaced with "zve64f"
392 - "Zve64d" should be replaced with "zve64d"
394 ``-device pvrdma`` and the rdma subsystem (since 8.2)
395 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
397 The pvrdma device and the whole rdma subsystem are in a bad shape and
398 without active maintenance. The QEMU project intends to remove this
399 device and subsystem from the code base in a future release without
400 replacement unless somebody steps up and improves the situation.
406 ``"backing": ""`` (since 2.12)
407 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
409 In order to prevent QEMU from automatically opening an image's backing
410 chain, use ``"backing": null`` instead.
412 ``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1)
413 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
415 Options for ``rbd`` should be specified according to its runtime options,
416 like other block drivers. Legacy parsing of keyvalue pair encoded
417 filenames is useful to open images with the old format for backing files;
418 These image files should be updated to use the current format.
420 Example of legacy encoding::
422 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}
424 The above, converted to the current supported format::
426 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
428 ``iscsi,password=xxx`` (since 8.0)
429 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
431 Specifying the iSCSI password in plain text on the command line using the
432 ``password`` option is insecure. The ``password-secret`` option should be
433 used instead, to refer to a ``--object secret...`` instance that provides
434 a password via a file, or encrypted.
436 CPU device properties
437 '''''''''''''''''''''
439 ``pmu-num=n`` on RISC-V CPUs (since 8.2)
440 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
442 In order to support more flexible counter configurations this has been replaced
443 by a ``pmu-mask`` property. If set of counters is continuous then the mask can
444 be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits
448 Backwards compatibility
449 -----------------------
451 Runnability guarantee of CPU models (since 4.1)
452 '''''''''''''''''''''''''''''''''''''''''''''''
454 Previous versions of QEMU never changed existing CPU models in
455 ways that introduced additional host software or hardware
456 requirements to the VM. This allowed management software to
457 safely change the machine type of an existing VM without
458 introducing new requirements ("runnability guarantee"). This
459 prevented CPU models from being updated to include CPU
460 vulnerability mitigations, leaving guests vulnerable in the
461 default configuration.
463 The CPU model runnability guarantee won't apply anymore to
464 existing CPU models. Management software that needs runnability
465 guarantees must resolve the CPU model aliases using the
466 ``alias-of`` field returned by the ``query-cpu-definitions`` QMP
469 While those guarantees are kept, the return value of
470 ``query-cpu-definitions`` will have existing CPU model aliases
471 point to a version that doesn't break runnability guarantees
472 (specifically, version 1 of those CPU models). In future QEMU
473 versions, aliases will point to newer CPU model versions
474 depending on the machine type, so management software must
475 resolve CPU model aliases before starting a virtual machine.
480 ``--blacklist`` command line option (since 7.2)
481 '''''''''''''''''''''''''''''''''''''''''''''''
483 ``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
484 wording for what this option does). The short form ``-b`` still stays
485 the same and thus is the preferred way for scripts that should run with
486 both, older and future versions of QEMU.
488 ``blacklist`` config file option (since 7.2)
489 ''''''''''''''''''''''''''''''''''''''''''''
491 The ``blacklist`` config file option has been renamed to ``block-rpcs``
492 (to be in sync with the renaming of the corresponding command line
498 ``skipped`` MigrationStats field (since 8.1)
499 ''''''''''''''''''''''''''''''''''''''''''''
501 ``skipped`` field in Migration stats has been deprecated. It hasn't
502 been used for more than 10 years.
504 ``inc`` migrate command option (since 8.2)
505 ''''''''''''''''''''''''''''''''''''''''''
507 Use blockdev-mirror with NBD instead.
509 As an intermediate step the ``inc`` functionality can be achieved by
510 setting the ``block-incremental`` migration parameter to ``true``.
511 But this parameter is also deprecated.
513 ``blk`` migrate command option (since 8.2)
514 ''''''''''''''''''''''''''''''''''''''''''
516 Use blockdev-mirror with NBD instead.
518 As an intermediate step the ``blk`` functionality can be achieved by
519 setting the ``block`` migration capability to ``true``. But this
520 capability is also deprecated.
522 block migration (since 8.2)
523 '''''''''''''''''''''''''''
525 Block migration is too inflexible. It needs to migrate all block
528 Please see "QMP invocation for live storage migration with
529 ``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst
530 for a detailed explanation.
532 old compression method (since 8.2)
533 ''''''''''''''''''''''''''''''''''
535 Compression method fails too much. Too many races. We are going to
536 remove it if nobody fixes it. For starters, migration-test
537 compression tests are disabled because they fail randomly. If you need
538 compression, use multifd compression methods.