xref: /openbmc/qemu/docs/about/deprecated.rst (revision 6c1e3906)
1.. _Deprecated features:
2
3Deprecated features
4===================
5
6In general features are intended to be supported indefinitely once
7introduced into QEMU. In the event that a feature needs to be removed,
8it will be listed in this section. The feature will remain functional for the
9release in which it was deprecated and one further release. After these two
10releases, the feature is liable to be removed. Deprecated features may also
11generate warnings on the console when QEMU starts up, or if activated via a
12monitor command, however, this is not a mandatory requirement.
13
14Prior to the 2.10.0 release there was no official policy on how
15long features would be deprecated prior to their removal, nor
16any documented list of which features were deprecated. Thus
17any features deprecated prior to 2.10.0 will be treated as if
18they were first deprecated in the 2.10.0 release.
19
20What follows is a list of all features currently marked as
21deprecated.
22
23Build options
24-------------
25
26``gprof`` builds (since 8.0)
27''''''''''''''''''''''''''''
28
29The ``--enable-gprof`` configure setting relies on compiler
30instrumentation to gather its data which can distort the generated
31profile. As other non-instrumenting tools are available that give a
32more holistic view of the system with non-instrumented binaries we are
33deprecating the build option and no longer defend it in CI. The
34``--enable-gcov`` build option remains for analysis test case
35coverage.
36
37System emulator command line arguments
38--------------------------------------
39
40``QEMU_AUDIO_`` environment variables and ``-audio-help`` (since 4.0)
41'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
42
43The ``-audiodev`` argument is now the preferred way to specify audio
44backend settings instead of environment variables.  To ease migration to
45the new format, the ``-audiodev-help`` option can be used to convert
46the current values of the environment variables to ``-audiodev`` options.
47
48Creating sound card devices and vnc without ``audiodev=`` property (since 4.2)
49''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
50
51When not using the deprecated legacy audio config, each sound card
52should specify an ``audiodev=`` property.  Additionally, when using
53vnc, you should specify an ``audiodev=`` property if you plan to
54transmit audio through the VNC protocol.
55
56Short-form boolean options (since 6.0)
57''''''''''''''''''''''''''''''''''''''
58
59Boolean options such as ``share=on``/``share=off`` could be written
60in short form as ``share`` and ``noshare``.  This is now deprecated
61and will cause a warning.
62
63``delay`` option for socket character devices (since 6.0)
64'''''''''''''''''''''''''''''''''''''''''''''''''''''''''
65
66The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on``
67rather than ``delay=off``.
68
69``-smp`` ("parameter=0" SMP configurations) (since 6.2)
70'''''''''''''''''''''''''''''''''''''''''''''''''''''''
71
72Specified CPU topology parameters must be greater than zero.
73
74In the SMP configuration, users should either provide a CPU topology
75parameter with a reasonable value (greater than zero) or just omit it
76and QEMU will compute the missing value.
77
78However, historically it was implicitly allowed for users to provide
79a parameter with zero value, which is meaningless and could also possibly
80cause unexpected results in the -smp parsing. So support for this kind of
81configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will
82be removed in the near future, users have to ensure that all the topology
83members described with -smp are greater than zero.
84
85Plugin argument passing through ``arg=<string>`` (since 6.1)
86''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
87
88Passing TCG plugins arguments through ``arg=`` is redundant is makes the
89command-line less readable, especially when the argument itself consist of a
90name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``.
91Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated
92as short-form boolean values, and passed to plugins as ``arg_name=on``.
93However, short-form booleans are deprecated and full explicit ``arg_name=on``
94form is preferred.
95
96``-no-hpet`` (since 8.0)
97''''''''''''''''''''''''
98
99The HPET setting has been turned into a machine property.
100Use ``-machine hpet=off`` instead.
101
102``-no-acpi`` (since 8.0)
103''''''''''''''''''''''''
104
105The ``-no-acpi`` setting has been turned into a machine property.
106Use ``-machine acpi=off`` instead.
107
108``-accel hax`` (since 8.0)
109''''''''''''''''''''''''''
110
111The HAXM project has been retired (see https://github.com/intel/haxm#status).
112Use "whpx" (on Windows) or "hvf" (on macOS) instead.
113
114``-async-teardown`` (since 8.1)
115'''''''''''''''''''''''''''''''
116
117Use ``-run-with async-teardown=on`` instead.
118
119``-singlestep`` (since 8.1)
120'''''''''''''''''''''''''''
121
122The ``-singlestep`` option has been turned into an accelerator property,
123and given a name that better reflects what it actually does.
124Use ``-accel tcg,one-insn-per-tb=on`` instead.
125
126User-mode emulator command line arguments
127-----------------------------------------
128
129``-singlestep`` (since 8.1)
130'''''''''''''''''''''''''''
131
132The ``-singlestep`` option has been given a name that better reflects
133what it actually does. For both linux-user and bsd-user, use the
134new ``-one-insn-per-tb`` option instead.
135
136QEMU Machine Protocol (QMP) commands
137------------------------------------
138
139``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8)
140'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
141
142Use argument ``id`` instead.
143
144``eject`` argument ``device`` (since 2.8)
145'''''''''''''''''''''''''''''''''''''''''
146
147Use argument ``id`` instead.
148
149``blockdev-change-medium`` argument ``device`` (since 2.8)
150''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
151
152Use argument ``id`` instead.
153
154``block_set_io_throttle`` argument ``device`` (since 2.8)
155'''''''''''''''''''''''''''''''''''''''''''''''''''''''''
156
157Use argument ``id`` instead.
158
159``blockdev-add`` empty string argument ``backing`` (since 2.10)
160'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
161
162Use argument value ``null`` instead.
163
164``block-commit`` arguments ``base`` and ``top`` (since 3.1)
165'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
166
167Use arguments ``base-node`` and ``top-node`` instead.
168
169``nbd-server-add`` and ``nbd-server-remove`` (since 5.2)
170''''''''''''''''''''''''''''''''''''''''''''''''''''''''
171
172Use the more generic commands ``block-export-add`` and ``block-export-del``
173instead.  As part of this deprecation, where ``nbd-server-add`` used a
174single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
175
176``query-qmp-schema`` return value member ``values`` (since 6.2)
177'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
178
179Member ``values`` in return value elements with meta-type ``enum`` is
180deprecated.  Use ``members`` instead.
181
182``drive-backup`` (since 6.2)
183''''''''''''''''''''''''''''
184
185Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
186This change primarily separates the creation/opening process of the backup
187target with explicit, separate steps. ``blockdev-backup`` uses mostly the
188same arguments as ``drive-backup``, except the ``format`` and ``mode``
189options are removed in favor of using explicit ``blockdev-create`` and
190``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
191details.
192
193Incorrectly typed ``device_add`` arguments (since 6.2)
194''''''''''''''''''''''''''''''''''''''''''''''''''''''
195
196Due to shortcomings in the internal implementation of ``device_add``, QEMU
197incorrectly accepts certain invalid arguments: Any object or list arguments are
198silently ignored. Other argument types are not checked, but an implicit
199conversion happens, so that e.g. string values can be assigned to integer
200device properties or vice versa.
201
202This is a bug in QEMU that will be fixed in the future so that previously
203accepted incorrect commands will return an error. Users should make sure that
204all arguments passed to ``device_add`` are consistent with the documented
205property types.
206
207``StatusInfo`` member ``singlestep`` (since 8.1)
208''''''''''''''''''''''''''''''''''''''''''''''''
209
210The ``singlestep`` member of the ``StatusInfo`` returned from the
211``query-status`` command is deprecated. This member has a confusing
212name and it never did what the documentation claimed or what its name
213suggests. We do not believe that anybody is actually using the
214information provided in this member.
215
216The information it reports is whether the TCG JIT is in "one
217instruction per translated block" mode (which can be set on the
218command line or via the HMP, but not via QMP). The information remains
219available via the HMP 'info jit' command.
220
221Human Monitor Protocol (HMP) commands
222-------------------------------------
223
224``singlestep`` (since 8.1)
225''''''''''''''''''''''''''
226
227The ``singlestep`` command has been replaced by the ``one-insn-per-tb``
228command, which has the same behaviour but a less misleading name.
229
230Host Architectures
231------------------
232
233BE MIPS (since 7.2)
234'''''''''''''''''''
235
236As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
237MIPS moved out of support making it hard to maintain our
238cross-compilation CI tests of the architecture. As we no longer have
239CI coverage support may bitrot away before the deprecation process
240completes. The little endian variants of MIPS (both 32 and 64 bit) are
241still a supported host architecture.
242
243System emulation on 32-bit x86 hosts (since 8.0)
244''''''''''''''''''''''''''''''''''''''''''''''''
245
246Support for 32-bit x86 host deployments is increasingly uncommon in mainstream
247OS distributions given the widespread availability of 64-bit x86 hardware.
248The QEMU project no longer considers 32-bit x86 support for system emulation to
249be an effective use of its limited resources, and thus intends to discontinue
250it. Since all recent x86 hardware from the past >10 years is capable of the
25164-bit x86 extensions, a corresponding 64-bit OS should be used instead.
252
253
254QEMU API (QAPI) events
255----------------------
256
257``MEM_UNPLUG_ERROR`` (since 6.2)
258''''''''''''''''''''''''''''''''''''''''''''''''''''''''
259
260Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.
261
262
263System emulator machines
264------------------------
265
266Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
267''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
268
269The ``dtb-kaslr-seed`` property on the ``virt`` board has been
270deprecated; use the new name ``dtb-randomness`` instead. The new name
271better reflects the way this property affects all random data within
272the device tree blob, not just the ``kaslr-seed`` node.
273
274``pc-i440fx-1.4`` up to ``pc-i440fx-1.7`` (since 7.0)
275'''''''''''''''''''''''''''''''''''''''''''''''''''''
276
277These old machine types are quite neglected nowadays and thus might have
278various pitfalls with regards to live migration. Use a newer machine type
279instead.
280
281
282Backend options
283---------------
284
285Using non-persistent backing file with pmem=on (since 6.1)
286''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
287
288This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
289device. However enabling ``memory-backend-file.pmem`` option, when backing file
290is (a) not DAX capable or (b) not on a filesystem that support direct mapping
291of persistent memory, is not safe and may lead to data loss or corruption in case
292of host crash.
293Options are:
294
295    - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
296      (without persistence guaranties) with backing file on non DAX storage
297    - move backing file to NVDIMM storage and keep ``pmem=on``
298      (to have NVDIMM with persistence guaranties).
299
300Device options
301--------------
302
303Emulated device options
304'''''''''''''''''''''''
305
306``-device virtio-blk,scsi=on|off`` (since 5.0)
307^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
308
309The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature.  VIRTIO 1.0
310and later do not support it because the virtio-scsi device was introduced for
311full SCSI support.  Use virtio-scsi instead when SCSI passthrough is required.
312
313Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
314alias.
315
316``-device nvme-ns,eui64-default=on|off`` (since 7.1)
317^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
318
319In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
320identifier that is not globally unique. If an EUI-64 identifier is required, the
321user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``.
322
323``-device nvme,use-intel-id=on|off`` (since 7.1)
324^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
325
326The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
327from Intel that was not properly allocated. Since version 5.2, the controller
328has used a properly allocated identifier. Deprecate the ``use-intel-id``
329machine compatibility parameter.
330
331
332Block device options
333''''''''''''''''''''
334
335``"backing": ""`` (since 2.12)
336^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
337
338In order to prevent QEMU from automatically opening an image's backing
339chain, use ``"backing": null`` instead.
340
341``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1)
342^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
343
344Options for ``rbd`` should be specified according to its runtime options,
345like other block drivers.  Legacy parsing of keyvalue pair encoded
346filenames is useful to open images with the old format for backing files;
347These image files should be updated to use the current format.
348
349Example of legacy encoding::
350
351  json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}
352
353The above, converted to the current supported format::
354
355  json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
356
357``iscsi,password=xxx`` (since 8.0)
358^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
359
360Specifying the iSCSI password in plain text on the command line using the
361``password`` option is insecure. The ``password-secret`` option should be
362used instead, to refer to a ``--object secret...`` instance that provides
363a password via a file, or encrypted.
364
365Backwards compatibility
366-----------------------
367
368Runnability guarantee of CPU models (since 4.1)
369'''''''''''''''''''''''''''''''''''''''''''''''
370
371Previous versions of QEMU never changed existing CPU models in
372ways that introduced additional host software or hardware
373requirements to the VM.  This allowed management software to
374safely change the machine type of an existing VM without
375introducing new requirements ("runnability guarantee").  This
376prevented CPU models from being updated to include CPU
377vulnerability mitigations, leaving guests vulnerable in the
378default configuration.
379
380The CPU model runnability guarantee won't apply anymore to
381existing CPU models.  Management software that needs runnability
382guarantees must resolve the CPU model aliases using the
383``alias-of`` field returned by the ``query-cpu-definitions`` QMP
384command.
385
386While those guarantees are kept, the return value of
387``query-cpu-definitions`` will have existing CPU model aliases
388point to a version that doesn't break runnability guarantees
389(specifically, version 1 of those CPU models).  In future QEMU
390versions, aliases will point to newer CPU model versions
391depending on the machine type, so management software must
392resolve CPU model aliases before starting a virtual machine.
393
394QEMU guest agent
395----------------
396
397``--blacklist`` command line option (since 7.2)
398'''''''''''''''''''''''''''''''''''''''''''''''
399
400``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
401wording for what this option does). The short form ``-b`` still stays
402the same and thus is the preferred way for scripts that should run with
403both, older and future versions of QEMU.
404
405``blacklist`` config file option (since 7.2)
406''''''''''''''''''''''''''''''''''''''''''''
407
408The ``blacklist`` config file option has been renamed to ``block-rpcs``
409(to be in sync with the renaming of the corresponding command line
410option).
411