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 Creating sound card devices without ``audiodev=`` property (since 4.2)
27 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
29 When not using the deprecated legacy audio config, each sound card
30 should specify an ``audiodev=`` property.
32 Short-form boolean options (since 6.0)
33 ''''''''''''''''''''''''''''''''''''''
35 Boolean options such as ``share=on``/``share=off`` could be written
36 in short form as ``share`` and ``noshare``. This is now deprecated
37 and will cause a warning.
39 ``delay`` option for socket character devices (since 6.0)
40 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
42 The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on``
43 rather than ``delay=off``.
45 ``-smp`` ("parameter=0" SMP configurations) (since 6.2)
46 '''''''''''''''''''''''''''''''''''''''''''''''''''''''
48 Specified CPU topology parameters must be greater than zero.
50 In the SMP configuration, users should either provide a CPU topology
51 parameter with a reasonable value (greater than zero) or just omit it
52 and QEMU will compute the missing value.
54 However, historically it was implicitly allowed for users to provide
55 a parameter with zero value, which is meaningless and could also possibly
56 cause unexpected results in the -smp parsing. So support for this kind of
57 configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will
58 be removed in the near future, users have to ensure that all the topology
59 members described with -smp are greater than zero.
61 Plugin argument passing through ``arg=<string>`` (since 6.1)
62 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
64 Passing TCG plugins arguments through ``arg=`` is redundant is makes the
65 command-line less readable, especially when the argument itself consist of a
66 name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``.
67 Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated
68 as short-form boolean values, and passed to plugins as ``arg_name=on``.
69 However, short-form booleans are deprecated and full explicit ``arg_name=on``
72 ``-no-hpet`` (since 8.0)
73 ''''''''''''''''''''''''
75 The HPET setting has been turned into a machine property.
76 Use ``-machine hpet=off`` instead.
78 ``-no-acpi`` (since 8.0)
79 ''''''''''''''''''''''''
81 The ``-no-acpi`` setting has been turned into a machine property.
82 Use ``-machine acpi=off`` instead.
84 ``-async-teardown`` (since 8.1)
85 '''''''''''''''''''''''''''''''
87 Use ``-run-with async-teardown=on`` instead.
89 ``-chroot`` (since 8.1)
90 '''''''''''''''''''''''
92 Use ``-run-with chroot=dir`` instead.
94 ``-singlestep`` (since 8.1)
95 '''''''''''''''''''''''''''
97 The ``-singlestep`` option has been turned into an accelerator property,
98 and given a name that better reflects what it actually does.
99 Use ``-accel tcg,one-insn-per-tb=on`` instead.
101 User-mode emulator command line arguments
102 -----------------------------------------
104 ``-singlestep`` (since 8.1)
105 '''''''''''''''''''''''''''
107 The ``-singlestep`` option has been given a name that better reflects
108 what it actually does. For both linux-user and bsd-user, use the
109 new ``-one-insn-per-tb`` option instead.
111 QEMU Machine Protocol (QMP) commands
112 ------------------------------------
114 ``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8)
115 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
117 Use argument ``id`` instead.
119 ``eject`` argument ``device`` (since 2.8)
120 '''''''''''''''''''''''''''''''''''''''''
122 Use argument ``id`` instead.
124 ``blockdev-change-medium`` argument ``device`` (since 2.8)
125 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
127 Use argument ``id`` instead.
129 ``block_set_io_throttle`` argument ``device`` (since 2.8)
130 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
132 Use argument ``id`` instead.
134 ``blockdev-add`` empty string argument ``backing`` (since 2.10)
135 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
137 Use argument value ``null`` instead.
139 ``block-commit`` arguments ``base`` and ``top`` (since 3.1)
140 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
142 Use arguments ``base-node`` and ``top-node`` instead.
144 ``nbd-server-add`` and ``nbd-server-remove`` (since 5.2)
145 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
147 Use the more generic commands ``block-export-add`` and ``block-export-del``
148 instead. As part of this deprecation, where ``nbd-server-add`` used a
149 single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
151 ``query-qmp-schema`` return value member ``values`` (since 6.2)
152 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
154 Member ``values`` in return value elements with meta-type ``enum`` is
155 deprecated. Use ``members`` instead.
157 ``drive-backup`` (since 6.2)
158 ''''''''''''''''''''''''''''
160 Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
161 This change primarily separates the creation/opening process of the backup
162 target with explicit, separate steps. ``blockdev-backup`` uses mostly the
163 same arguments as ``drive-backup``, except the ``format`` and ``mode``
164 options are removed in favor of using explicit ``blockdev-create`` and
165 ``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
168 Incorrectly typed ``device_add`` arguments (since 6.2)
169 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
171 Due to shortcomings in the internal implementation of ``device_add``, QEMU
172 incorrectly accepts certain invalid arguments: Any object or list arguments are
173 silently ignored. Other argument types are not checked, but an implicit
174 conversion happens, so that e.g. string values can be assigned to integer
175 device properties or vice versa.
177 This is a bug in QEMU that will be fixed in the future so that previously
178 accepted incorrect commands will return an error. Users should make sure that
179 all arguments passed to ``device_add`` are consistent with the documented
182 ``StatusInfo`` member ``singlestep`` (since 8.1)
183 ''''''''''''''''''''''''''''''''''''''''''''''''
185 The ``singlestep`` member of the ``StatusInfo`` returned from the
186 ``query-status`` command is deprecated. This member has a confusing
187 name and it never did what the documentation claimed or what its name
188 suggests. We do not believe that anybody is actually using the
189 information provided in this member.
191 The information it reports is whether the TCG JIT is in "one
192 instruction per translated block" mode (which can be set on the
193 command line or via the HMP, but not via QMP). The information remains
194 available via the HMP 'info jit' command.
196 QEMU Machine Protocol (QMP) events
197 ----------------------------------
199 ``MEM_UNPLUG_ERROR`` (since 6.2)
200 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
202 Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.
204 ``vcpu`` trace events (since 8.1)
205 '''''''''''''''''''''''''''''''''
207 The ability to instrument QEMU helper functions with vCPU-aware trace
208 points was removed in 7.0. However QMP still exposed the vcpu
209 parameter. This argument has now been deprecated and the remaining
210 remaining trace points that used it are selected just by name.
212 Human Monitor Protocol (HMP) commands
213 -------------------------------------
215 ``singlestep`` (since 8.1)
216 ''''''''''''''''''''''''''
218 The ``singlestep`` command has been replaced by the ``one-insn-per-tb``
219 command, which has the same behaviour but a less misleading name.
227 As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
228 MIPS moved out of support making it hard to maintain our
229 cross-compilation CI tests of the architecture. As we no longer have
230 CI coverage support may bitrot away before the deprecation process
231 completes. The little endian variants of MIPS (both 32 and 64 bit) are
232 still a supported host architecture.
234 System emulation on 32-bit x86 hosts (since 8.0)
235 ''''''''''''''''''''''''''''''''''''''''''''''''
237 Support for 32-bit x86 host deployments is increasingly uncommon in mainstream
238 OS distributions given the widespread availability of 64-bit x86 hardware.
239 The QEMU project no longer considers 32-bit x86 support for system emulation to
240 be an effective use of its limited resources, and thus intends to discontinue
241 it. Since all recent x86 hardware from the past >10 years is capable of the
242 64-bit x86 extensions, a corresponding 64-bit OS should be used instead.
245 System emulator machines
246 ------------------------
248 Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
249 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
251 The ``dtb-kaslr-seed`` property on the ``virt`` board has been
252 deprecated; use the new name ``dtb-randomness`` instead. The new name
253 better reflects the way this property affects all random data within
254 the device tree blob, not just the ``kaslr-seed`` node.
259 Using non-persistent backing file with pmem=on (since 6.1)
260 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
262 This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
263 device. However enabling ``memory-backend-file.pmem`` option, when backing file
264 is (a) not DAX capable or (b) not on a filesystem that support direct mapping
265 of persistent memory, is not safe and may lead to data loss or corruption in case
269 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
270 (without persistence guaranties) with backing file on non DAX storage
271 - move backing file to NVDIMM storage and keep ``pmem=on``
272 (to have NVDIMM with persistence guaranties).
277 Emulated device options
278 '''''''''''''''''''''''
280 ``-device virtio-blk,scsi=on|off`` (since 5.0)
281 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
283 The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0
284 and later do not support it because the virtio-scsi device was introduced for
285 full SCSI support. Use virtio-scsi instead when SCSI passthrough is required.
287 Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
290 ``-device nvme-ns,eui64-default=on|off`` (since 7.1)
291 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
293 In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
294 identifier that is not globally unique. If an EUI-64 identifier is required, the
295 user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``.
297 ``-device nvme,use-intel-id=on|off`` (since 7.1)
298 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
300 The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
301 from Intel that was not properly allocated. Since version 5.2, the controller
302 has used a properly allocated identifier. Deprecate the ``use-intel-id``
303 machine compatibility parameter.
305 ``-device cxl-type3,memdev=xxxx`` (since 8.0)
306 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
308 The ``cxl-type3`` device initially only used a single memory backend. With
309 the addition of volatile memory support, it is now necessary to distinguish
310 between persistent and volatile memory backends. As such, memdev is deprecated
311 in favor of persistent-memdev.
313 ``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1)
314 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
316 The 9p ``proxy`` filesystem backend driver has been deprecated and will be
317 removed (along with its proxy helper daemon) in a future version of QEMU. Please
318 use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem
319 backend, or alternatively consider deploying virtiofsd instead.
321 The 9p ``proxy`` backend was originally developed as an alternative to the 9p
322 ``local`` backend. The idea was to enhance security by dispatching actual low
323 level filesystem operations from 9p server (QEMU process) over to a separate
324 process (the virtfs-proxy-helper binary). However this alternative never gained
325 momentum. The proxy backend is much slower than the local backend, hasn't seen
326 any development in years, and showed to be less secure, especially due to the
327 fact that its helper daemon must be run as root, whereas with the local backend
328 QEMU is typically run as unprivileged user and allows to tighten behaviour by
329 mapping permissions et al by using its 'mapped' security model option.
331 Nowadays it would make sense to reimplement the ``proxy`` backend by using
332 QEMU's ``vhost`` feature, which would eliminate the high latency costs under
333 which the 9p ``proxy`` backend currently suffers. However as of to date nobody
334 has indicated plans for such kind of reimplementation unfortunately.
340 ``"backing": ""`` (since 2.12)
341 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
343 In order to prevent QEMU from automatically opening an image's backing
344 chain, use ``"backing": null`` instead.
346 ``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1)
347 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
349 Options for ``rbd`` should be specified according to its runtime options,
350 like other block drivers. Legacy parsing of keyvalue pair encoded
351 filenames is useful to open images with the old format for backing files;
352 These image files should be updated to use the current format.
354 Example of legacy encoding::
356 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}
358 The above, converted to the current supported format::
360 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
362 ``iscsi,password=xxx`` (since 8.0)
363 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
365 Specifying the iSCSI password in plain text on the command line using the
366 ``password`` option is insecure. The ``password-secret`` option should be
367 used instead, to refer to a ``--object secret...`` instance that provides
368 a password via a file, or encrypted.
370 Backwards compatibility
371 -----------------------
373 Runnability guarantee of CPU models (since 4.1)
374 '''''''''''''''''''''''''''''''''''''''''''''''
376 Previous versions of QEMU never changed existing CPU models in
377 ways that introduced additional host software or hardware
378 requirements to the VM. This allowed management software to
379 safely change the machine type of an existing VM without
380 introducing new requirements ("runnability guarantee"). This
381 prevented CPU models from being updated to include CPU
382 vulnerability mitigations, leaving guests vulnerable in the
383 default configuration.
385 The CPU model runnability guarantee won't apply anymore to
386 existing CPU models. Management software that needs runnability
387 guarantees must resolve the CPU model aliases using the
388 ``alias-of`` field returned by the ``query-cpu-definitions`` QMP
391 While those guarantees are kept, the return value of
392 ``query-cpu-definitions`` will have existing CPU model aliases
393 point to a version that doesn't break runnability guarantees
394 (specifically, version 1 of those CPU models). In future QEMU
395 versions, aliases will point to newer CPU model versions
396 depending on the machine type, so management software must
397 resolve CPU model aliases before starting a virtual machine.
402 ``--blacklist`` command line option (since 7.2)
403 '''''''''''''''''''''''''''''''''''''''''''''''
405 ``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
406 wording for what this option does). The short form ``-b`` still stays
407 the same and thus is the preferred way for scripts that should run with
408 both, older and future versions of QEMU.
410 ``blacklist`` config file option (since 7.2)
411 ''''''''''''''''''''''''''''''''''''''''''''
413 The ``blacklist`` config file option has been renamed to ``block-rpcs``
414 (to be in sync with the renaming of the corresponding command line
420 ``skipped`` MigrationStats field (since 8.1)
421 ''''''''''''''''''''''''''''''''''''''''''''
423 ``skipped`` field in Migration stats has been deprecated. It hasn't
424 been used for more than 10 years.