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 ``-singlestep`` (since 8.1)
67 '''''''''''''''''''''''''''
69 The ``-singlestep`` option has been turned into an accelerator property,
70 and given a name that better reflects what it actually does.
71 Use ``-accel tcg,one-insn-per-tb=on`` instead.
73 User-mode emulator command line arguments
74 -----------------------------------------
76 ``-singlestep`` (since 8.1)
77 '''''''''''''''''''''''''''
79 The ``-singlestep`` option has been given a name that better reflects
80 what it actually does. For both linux-user and bsd-user, use the
81 new ``-one-insn-per-tb`` option instead.
83 QEMU Machine Protocol (QMP) commands
84 ------------------------------------
86 ``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8)
87 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
89 Use argument ``id`` instead.
91 ``eject`` argument ``device`` (since 2.8)
92 '''''''''''''''''''''''''''''''''''''''''
94 Use argument ``id`` instead.
96 ``blockdev-change-medium`` argument ``device`` (since 2.8)
97 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
99 Use argument ``id`` instead.
101 ``block_set_io_throttle`` argument ``device`` (since 2.8)
102 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
104 Use argument ``id`` instead.
106 ``blockdev-add`` empty string argument ``backing`` (since 2.10)
107 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
109 Use argument value ``null`` instead.
111 ``block-commit`` arguments ``base`` and ``top`` (since 3.1)
112 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
114 Use arguments ``base-node`` and ``top-node`` instead.
116 ``nbd-server-add`` and ``nbd-server-remove`` (since 5.2)
117 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
119 Use the more generic commands ``block-export-add`` and ``block-export-del``
120 instead. As part of this deprecation, where ``nbd-server-add`` used a
121 single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
123 ``query-qmp-schema`` return value member ``values`` (since 6.2)
124 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
126 Member ``values`` in return value elements with meta-type ``enum`` is
127 deprecated. Use ``members`` instead.
129 ``drive-backup`` (since 6.2)
130 ''''''''''''''''''''''''''''
132 Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
133 This change primarily separates the creation/opening process of the backup
134 target with explicit, separate steps. ``blockdev-backup`` uses mostly the
135 same arguments as ``drive-backup``, except the ``format`` and ``mode``
136 options are removed in favor of using explicit ``blockdev-create`` and
137 ``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
140 Incorrectly typed ``device_add`` arguments (since 6.2)
141 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
143 Due to shortcomings in the internal implementation of ``device_add``, QEMU
144 incorrectly accepts certain invalid arguments: Any object or list arguments are
145 silently ignored. Other argument types are not checked, but an implicit
146 conversion happens, so that e.g. string values can be assigned to integer
147 device properties or vice versa.
149 This is a bug in QEMU that will be fixed in the future so that previously
150 accepted incorrect commands will return an error. Users should make sure that
151 all arguments passed to ``device_add`` are consistent with the documented
154 QEMU Machine Protocol (QMP) events
155 ----------------------------------
157 ``MEM_UNPLUG_ERROR`` (since 6.2)
158 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
160 Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.
162 ``vcpu`` trace events (since 8.1)
163 '''''''''''''''''''''''''''''''''
165 The ability to instrument QEMU helper functions with vCPU-aware trace
166 points was removed in 7.0. However QMP still exposed the vcpu
167 parameter. This argument has now been deprecated and the remaining
168 remaining trace points that used it are selected just by name.
176 As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
177 MIPS moved out of support making it hard to maintain our
178 cross-compilation CI tests of the architecture. As we no longer have
179 CI coverage support may bitrot away before the deprecation process
180 completes. The little endian variants of MIPS (both 32 and 64 bit) are
181 still a supported host architecture.
183 System emulation on 32-bit x86 hosts (since 8.0)
184 ''''''''''''''''''''''''''''''''''''''''''''''''
186 Support for 32-bit x86 host deployments is increasingly uncommon in mainstream
187 OS distributions given the widespread availability of 64-bit x86 hardware.
188 The QEMU project no longer considers 32-bit x86 support for system emulation to
189 be an effective use of its limited resources, and thus intends to discontinue
190 it. Since all recent x86 hardware from the past >10 years is capable of the
191 64-bit x86 extensions, a corresponding 64-bit OS should be used instead.
197 Nios II CPU (since 8.2)
198 '''''''''''''''''''''''
200 The Nios II architecture is orphan. The ``nios2`` guest CPU support is
201 deprecated and will be removed in a future version of QEMU.
204 System emulator machines
205 ------------------------
207 Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
208 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
210 The ``dtb-kaslr-seed`` property on the ``virt`` board has been
211 deprecated; use the new name ``dtb-randomness`` instead. The new name
212 better reflects the way this property affects all random data within
213 the device tree blob, not just the ``kaslr-seed`` node.
215 ``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2)
216 '''''''''''''''''''''''''''''''''''''''''''''''''''''
218 These old machine types are quite neglected nowadays and thus might have
219 various pitfalls with regards to live migration. Use a newer machine type
222 Nios II ``10m50-ghrd`` and ``nios2-generic-nommu`` machines (since 8.2)
223 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
225 The Nios II architecture is orphan.
231 Using non-persistent backing file with pmem=on (since 6.1)
232 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
234 This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
235 device. However enabling ``memory-backend-file.pmem`` option, when backing file
236 is (a) not DAX capable or (b) not on a filesystem that support direct mapping
237 of persistent memory, is not safe and may lead to data loss or corruption in case
241 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
242 (without persistence guaranties) with backing file on non DAX storage
243 - move backing file to NVDIMM storage and keep ``pmem=on``
244 (to have NVDIMM with persistence guaranties).
249 Emulated device options
250 '''''''''''''''''''''''
252 ``-device virtio-blk,scsi=on|off`` (since 5.0)
253 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
255 The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0
256 and later do not support it because the virtio-scsi device was introduced for
257 full SCSI support. Use virtio-scsi instead when SCSI passthrough is required.
259 Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
262 ``-device nvme-ns,eui64-default=on|off`` (since 7.1)
263 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
265 In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
266 identifier that is not globally unique. If an EUI-64 identifier is required, the
267 user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``.
269 ``-device nvme,use-intel-id=on|off`` (since 7.1)
270 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
272 The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
273 from Intel that was not properly allocated. Since version 5.2, the controller
274 has used a properly allocated identifier. Deprecate the ``use-intel-id``
275 machine compatibility parameter.
277 ``-device cxl-type3,memdev=xxxx`` (since 8.0)
278 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
280 The ``cxl-type3`` device initially only used a single memory backend. With
281 the addition of volatile memory support, it is now necessary to distinguish
282 between persistent and volatile memory backends. As such, memdev is deprecated
283 in favor of persistent-memdev.
285 ``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1)
286 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
288 The 9p ``proxy`` filesystem backend driver has been deprecated and will be
289 removed (along with its proxy helper daemon) in a future version of QEMU. Please
290 use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem
291 backend, or alternatively consider deploying virtiofsd instead.
293 The 9p ``proxy`` backend was originally developed as an alternative to the 9p
294 ``local`` backend. The idea was to enhance security by dispatching actual low
295 level filesystem operations from 9p server (QEMU process) over to a separate
296 process (the virtfs-proxy-helper binary). However this alternative never gained
297 momentum. The proxy backend is much slower than the local backend, hasn't seen
298 any development in years, and showed to be less secure, especially due to the
299 fact that its helper daemon must be run as root, whereas with the local backend
300 QEMU is typically run as unprivileged user and allows to tighten behaviour by
301 mapping permissions et al by using its 'mapped' security model option.
303 Nowadays it would make sense to reimplement the ``proxy`` backend by using
304 QEMU's ``vhost`` feature, which would eliminate the high latency costs under
305 which the 9p ``proxy`` backend currently suffers. However as of to date nobody
306 has indicated plans for such kind of reimplementation unfortunately.
308 RISC-V 'any' CPU type ``-cpu any`` (since 8.2)
309 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
311 The 'any' CPU type was introduced back in 2018 and has been around since the
312 initial RISC-V QEMU port. Its usage has always been unclear: users don't know
313 what to expect from a CPU called 'any', and in fact the CPU does not do anything
314 special that isn't already done by the default CPUs rv32/rv64.
316 After the introduction of the 'max' CPU type, RISC-V now has a good coverage
317 of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete
318 CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any'
319 CPU type starting in 8.2.
321 RISC-V CPU properties which start with capital 'Z' (since 8.2)
322 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
324 All RISC-V CPU properties which start with capital 'Z' are being deprecated
325 starting in 8.2. The reason is that they were wrongly added with capital 'Z'
326 in the past. CPU properties were later added with lower-case names, which
327 is the format we want to use from now on.
329 Users which try to use these deprecated properties will receive a warning
330 recommending to switch to their stable counterparts:
332 - "Zifencei" should be replaced with "zifencei"
333 - "Zicsr" should be replaced with "zicsr"
334 - "Zihintntl" should be replaced with "zihintntl"
335 - "Zihintpause" should be replaced with "zihintpause"
336 - "Zawrs" should be replaced with "zawrs"
337 - "Zfa" should be replaced with "zfa"
338 - "Zfh" should be replaced with "zfh"
339 - "Zfhmin" should be replaced with "zfhmin"
340 - "Zve32f" should be replaced with "zve32f"
341 - "Zve64f" should be replaced with "zve64f"
342 - "Zve64d" should be replaced with "zve64d"
344 ``-device pvrdma`` and the rdma subsystem (since 8.2)
345 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
347 The pvrdma device and the whole rdma subsystem are in a bad shape and
348 without active maintenance. The QEMU project intends to remove this
349 device and subsystem from the code base in a future release without
350 replacement unless somebody steps up and improves the situation.
356 ``"backing": ""`` (since 2.12)
357 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
359 In order to prevent QEMU from automatically opening an image's backing
360 chain, use ``"backing": null`` instead.
362 ``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1)
363 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
365 Options for ``rbd`` should be specified according to its runtime options,
366 like other block drivers. Legacy parsing of keyvalue pair encoded
367 filenames is useful to open images with the old format for backing files;
368 These image files should be updated to use the current format.
370 Example of legacy encoding::
372 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}
374 The above, converted to the current supported format::
376 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
378 ``iscsi,password=xxx`` (since 8.0)
379 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
381 Specifying the iSCSI password in plain text on the command line using the
382 ``password`` option is insecure. The ``password-secret`` option should be
383 used instead, to refer to a ``--object secret...`` instance that provides
384 a password via a file, or encrypted.
386 CPU device properties
387 '''''''''''''''''''''
389 ``pmu-num=n`` on RISC-V CPUs (since 8.2)
390 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
392 In order to support more flexible counter configurations this has been replaced
393 by a ``pmu-mask`` property. If set of counters is continuous then the mask can
394 be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits
398 Backwards compatibility
399 -----------------------
401 Runnability guarantee of CPU models (since 4.1)
402 '''''''''''''''''''''''''''''''''''''''''''''''
404 Previous versions of QEMU never changed existing CPU models in
405 ways that introduced additional host software or hardware
406 requirements to the VM. This allowed management software to
407 safely change the machine type of an existing VM without
408 introducing new requirements ("runnability guarantee"). This
409 prevented CPU models from being updated to include CPU
410 vulnerability mitigations, leaving guests vulnerable in the
411 default configuration.
413 The CPU model runnability guarantee won't apply anymore to
414 existing CPU models. Management software that needs runnability
415 guarantees must resolve the CPU model aliases using the
416 ``alias-of`` field returned by the ``query-cpu-definitions`` QMP
419 While those guarantees are kept, the return value of
420 ``query-cpu-definitions`` will have existing CPU model aliases
421 point to a version that doesn't break runnability guarantees
422 (specifically, version 1 of those CPU models). In future QEMU
423 versions, aliases will point to newer CPU model versions
424 depending on the machine type, so management software must
425 resolve CPU model aliases before starting a virtual machine.
430 ``--blacklist`` command line option (since 7.2)
431 '''''''''''''''''''''''''''''''''''''''''''''''
433 ``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
434 wording for what this option does). The short form ``-b`` still stays
435 the same and thus is the preferred way for scripts that should run with
436 both, older and future versions of QEMU.
438 ``blacklist`` config file option (since 7.2)
439 ''''''''''''''''''''''''''''''''''''''''''''
441 The ``blacklist`` config file option has been renamed to ``block-rpcs``
442 (to be in sync with the renaming of the corresponding command line
448 ``skipped`` MigrationStats field (since 8.1)
449 ''''''''''''''''''''''''''''''''''''''''''''
451 ``skipped`` field in Migration stats has been deprecated. It hasn't
452 been used for more than 10 years.
454 ``inc`` migrate command option (since 8.2)
455 ''''''''''''''''''''''''''''''''''''''''''
457 Use blockdev-mirror with NBD instead.
459 As an intermediate step the ``inc`` functionality can be achieved by
460 setting the ``block-incremental`` migration parameter to ``true``.
461 But this parameter is also deprecated.
463 ``blk`` migrate command option (since 8.2)
464 ''''''''''''''''''''''''''''''''''''''''''
466 Use blockdev-mirror with NBD instead.
468 As an intermediate step the ``blk`` functionality can be achieved by
469 setting the ``block`` migration capability to ``true``. But this
470 capability is also deprecated.
472 block migration (since 8.2)
473 '''''''''''''''''''''''''''
475 Block migration is too inflexible. It needs to migrate all block
478 Please see "QMP invocation for live storage migration with
479 ``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst
480 for a detailed explanation.
482 old compression method (since 8.2)
483 ''''''''''''''''''''''''''''''''''
485 Compression method fails too much. Too many races. We are going to
486 remove it if nobody fixes it. For starters, migration-test
487 compression tests are disabled because they fail randomly. If you need
488 compression, use multifd compression methods.