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``-chroot`` (since 8.1) 120''''''''''''''''''''''' 121 122Use ``-run-with chroot=dir`` instead. 123 124``-singlestep`` (since 8.1) 125''''''''''''''''''''''''''' 126 127The ``-singlestep`` option has been turned into an accelerator property, 128and given a name that better reflects what it actually does. 129Use ``-accel tcg,one-insn-per-tb=on`` instead. 130 131User-mode emulator command line arguments 132----------------------------------------- 133 134``-singlestep`` (since 8.1) 135''''''''''''''''''''''''''' 136 137The ``-singlestep`` option has been given a name that better reflects 138what it actually does. For both linux-user and bsd-user, use the 139new ``-one-insn-per-tb`` option instead. 140 141QEMU Machine Protocol (QMP) commands 142------------------------------------ 143 144``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 145''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 146 147Use argument ``id`` instead. 148 149``eject`` argument ``device`` (since 2.8) 150''''''''''''''''''''''''''''''''''''''''' 151 152Use argument ``id`` instead. 153 154``blockdev-change-medium`` argument ``device`` (since 2.8) 155'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 156 157Use argument ``id`` instead. 158 159``block_set_io_throttle`` argument ``device`` (since 2.8) 160''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 161 162Use argument ``id`` instead. 163 164``blockdev-add`` empty string argument ``backing`` (since 2.10) 165''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 166 167Use argument value ``null`` instead. 168 169``block-commit`` arguments ``base`` and ``top`` (since 3.1) 170''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 171 172Use arguments ``base-node`` and ``top-node`` instead. 173 174``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 175'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 176 177Use the more generic commands ``block-export-add`` and ``block-export-del`` 178instead. As part of this deprecation, where ``nbd-server-add`` used a 179single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 180 181``query-qmp-schema`` return value member ``values`` (since 6.2) 182''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 183 184Member ``values`` in return value elements with meta-type ``enum`` is 185deprecated. Use ``members`` instead. 186 187``drive-backup`` (since 6.2) 188'''''''''''''''''''''''''''' 189 190Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 191This change primarily separates the creation/opening process of the backup 192target with explicit, separate steps. ``blockdev-backup`` uses mostly the 193same arguments as ``drive-backup``, except the ``format`` and ``mode`` 194options are removed in favor of using explicit ``blockdev-create`` and 195``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 196details. 197 198Incorrectly typed ``device_add`` arguments (since 6.2) 199'''''''''''''''''''''''''''''''''''''''''''''''''''''' 200 201Due to shortcomings in the internal implementation of ``device_add``, QEMU 202incorrectly accepts certain invalid arguments: Any object or list arguments are 203silently ignored. Other argument types are not checked, but an implicit 204conversion happens, so that e.g. string values can be assigned to integer 205device properties or vice versa. 206 207This is a bug in QEMU that will be fixed in the future so that previously 208accepted incorrect commands will return an error. Users should make sure that 209all arguments passed to ``device_add`` are consistent with the documented 210property types. 211 212``StatusInfo`` member ``singlestep`` (since 8.1) 213'''''''''''''''''''''''''''''''''''''''''''''''' 214 215The ``singlestep`` member of the ``StatusInfo`` returned from the 216``query-status`` command is deprecated. This member has a confusing 217name and it never did what the documentation claimed or what its name 218suggests. We do not believe that anybody is actually using the 219information provided in this member. 220 221The information it reports is whether the TCG JIT is in "one 222instruction per translated block" mode (which can be set on the 223command line or via the HMP, but not via QMP). The information remains 224available via the HMP 'info jit' command. 225 226QEMU Machine Protocol (QMP) events 227---------------------------------- 228 229``MEM_UNPLUG_ERROR`` (since 6.2) 230'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 231 232Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead. 233 234``vcpu`` trace events (since 8.1) 235''''''''''''''''''''''''''''''''' 236 237The ability to instrument QEMU helper functions with vCPU-aware trace 238points was removed in 7.0. However QMP still exposed the vcpu 239parameter. This argument has now been deprecated and the remaining 240remaining trace points that used it are selected just by name. 241 242Human Monitor Protocol (HMP) commands 243------------------------------------- 244 245``singlestep`` (since 8.1) 246'''''''''''''''''''''''''' 247 248The ``singlestep`` command has been replaced by the ``one-insn-per-tb`` 249command, which has the same behaviour but a less misleading name. 250 251Host Architectures 252------------------ 253 254BE MIPS (since 7.2) 255''''''''''''''''''' 256 257As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 258MIPS moved out of support making it hard to maintain our 259cross-compilation CI tests of the architecture. As we no longer have 260CI coverage support may bitrot away before the deprecation process 261completes. The little endian variants of MIPS (both 32 and 64 bit) are 262still a supported host architecture. 263 264System emulation on 32-bit x86 hosts (since 8.0) 265'''''''''''''''''''''''''''''''''''''''''''''''' 266 267Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 268OS distributions given the widespread availability of 64-bit x86 hardware. 269The QEMU project no longer considers 32-bit x86 support for system emulation to 270be an effective use of its limited resources, and thus intends to discontinue 271it. Since all recent x86 hardware from the past >10 years is capable of the 27264-bit x86 extensions, a corresponding 64-bit OS should be used instead. 273 274 275System emulator machines 276------------------------ 277 278Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 279'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 280 281The ``dtb-kaslr-seed`` property on the ``virt`` board has been 282deprecated; use the new name ``dtb-randomness`` instead. The new name 283better reflects the way this property affects all random data within 284the device tree blob, not just the ``kaslr-seed`` node. 285 286``pc-i440fx-1.4`` up to ``pc-i440fx-1.7`` (since 7.0) 287''''''''''''''''''''''''''''''''''''''''''''''''''''' 288 289These old machine types are quite neglected nowadays and thus might have 290various pitfalls with regards to live migration. Use a newer machine type 291instead. 292 293 294Backend options 295--------------- 296 297Using non-persistent backing file with pmem=on (since 6.1) 298'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 299 300This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 301device. However enabling ``memory-backend-file.pmem`` option, when backing file 302is (a) not DAX capable or (b) not on a filesystem that support direct mapping 303of persistent memory, is not safe and may lead to data loss or corruption in case 304of host crash. 305Options are: 306 307 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 308 (without persistence guaranties) with backing file on non DAX storage 309 - move backing file to NVDIMM storage and keep ``pmem=on`` 310 (to have NVDIMM with persistence guaranties). 311 312Device options 313-------------- 314 315Emulated device options 316''''''''''''''''''''''' 317 318``-device virtio-blk,scsi=on|off`` (since 5.0) 319^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 320 321The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 322and later do not support it because the virtio-scsi device was introduced for 323full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 324 325Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 326alias. 327 328``-device nvme-ns,eui64-default=on|off`` (since 7.1) 329^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 330 331In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 332identifier that is not globally unique. If an EUI-64 identifier is required, the 333user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 334 335``-device nvme,use-intel-id=on|off`` (since 7.1) 336^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 337 338The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 339from Intel that was not properly allocated. Since version 5.2, the controller 340has used a properly allocated identifier. Deprecate the ``use-intel-id`` 341machine compatibility parameter. 342 343``-device cxl-type3,memdev=xxxx`` (since 8.0) 344^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 345 346The ``cxl-type3`` device initially only used a single memory backend. With 347the addition of volatile memory support, it is now necessary to distinguish 348between persistent and volatile memory backends. As such, memdev is deprecated 349in favor of persistent-memdev. 350 351``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 352^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 353 354The 9p ``proxy`` filesystem backend driver has been deprecated and will be 355removed (along with its proxy helper daemon) in a future version of QEMU. Please 356use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 357backend, or alternatively consider deploying virtiofsd instead. 358 359The 9p ``proxy`` backend was originally developed as an alternative to the 9p 360``local`` backend. The idea was to enhance security by dispatching actual low 361level filesystem operations from 9p server (QEMU process) over to a separate 362process (the virtfs-proxy-helper binary). However this alternative never gained 363momentum. The proxy backend is much slower than the local backend, hasn't seen 364any development in years, and showed to be less secure, especially due to the 365fact that its helper daemon must be run as root, whereas with the local backend 366QEMU is typically run as unprivileged user and allows to tighten behaviour by 367mapping permissions et al by using its 'mapped' security model option. 368 369Nowadays it would make sense to reimplement the ``proxy`` backend by using 370QEMU's ``vhost`` feature, which would eliminate the high latency costs under 371which the 9p ``proxy`` backend currently suffers. However as of to date nobody 372has indicated plans for such kind of reimplementation unfortunately. 373 374 375Block device options 376'''''''''''''''''''' 377 378``"backing": ""`` (since 2.12) 379^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 380 381In order to prevent QEMU from automatically opening an image's backing 382chain, use ``"backing": null`` instead. 383 384``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 385^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 386 387Options for ``rbd`` should be specified according to its runtime options, 388like other block drivers. Legacy parsing of keyvalue pair encoded 389filenames is useful to open images with the old format for backing files; 390These image files should be updated to use the current format. 391 392Example of legacy encoding:: 393 394 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 395 396The above, converted to the current supported format:: 397 398 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 399 400``iscsi,password=xxx`` (since 8.0) 401^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 402 403Specifying the iSCSI password in plain text on the command line using the 404``password`` option is insecure. The ``password-secret`` option should be 405used instead, to refer to a ``--object secret...`` instance that provides 406a password via a file, or encrypted. 407 408Backwards compatibility 409----------------------- 410 411Runnability guarantee of CPU models (since 4.1) 412''''''''''''''''''''''''''''''''''''''''''''''' 413 414Previous versions of QEMU never changed existing CPU models in 415ways that introduced additional host software or hardware 416requirements to the VM. This allowed management software to 417safely change the machine type of an existing VM without 418introducing new requirements ("runnability guarantee"). This 419prevented CPU models from being updated to include CPU 420vulnerability mitigations, leaving guests vulnerable in the 421default configuration. 422 423The CPU model runnability guarantee won't apply anymore to 424existing CPU models. Management software that needs runnability 425guarantees must resolve the CPU model aliases using the 426``alias-of`` field returned by the ``query-cpu-definitions`` QMP 427command. 428 429While those guarantees are kept, the return value of 430``query-cpu-definitions`` will have existing CPU model aliases 431point to a version that doesn't break runnability guarantees 432(specifically, version 1 of those CPU models). In future QEMU 433versions, aliases will point to newer CPU model versions 434depending on the machine type, so management software must 435resolve CPU model aliases before starting a virtual machine. 436 437QEMU guest agent 438---------------- 439 440``--blacklist`` command line option (since 7.2) 441''''''''''''''''''''''''''''''''''''''''''''''' 442 443``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 444wording for what this option does). The short form ``-b`` still stays 445the same and thus is the preferred way for scripts that should run with 446both, older and future versions of QEMU. 447 448``blacklist`` config file option (since 7.2) 449'''''''''''''''''''''''''''''''''''''''''''' 450 451The ``blacklist`` config file option has been renamed to ``block-rpcs`` 452(to be in sync with the renaming of the corresponding command line 453option). 454 455Migration 456--------- 457 458``skipped`` MigrationStats field (since 8.1) 459'''''''''''''''''''''''''''''''''''''''''''' 460 461``skipped`` field in Migration stats has been deprecated. It hasn't 462been used for more than 10 years. 463 464