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 23System emulator command line arguments 24-------------------------------------- 25 26Short-form boolean options (since 6.0) 27'''''''''''''''''''''''''''''''''''''' 28 29Boolean options such as ``share=on``/``share=off`` could be written 30in short form as ``share`` and ``noshare``. This is now deprecated 31and will cause a warning. 32 33``delay`` option for socket character devices (since 6.0) 34''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 35 36The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on`` 37rather than ``delay=off``. 38 39Plugin argument passing through ``arg=<string>`` (since 6.1) 40'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 41 42Passing TCG plugins arguments through ``arg=`` is redundant is makes the 43command-line less readable, especially when the argument itself consist of a 44name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``. 45Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated 46as short-form boolean values, and passed to plugins as ``arg_name=on``. 47However, short-form booleans are deprecated and full explicit ``arg_name=on`` 48form is preferred. 49 50``-smp`` (Unsupported "parameter=1" SMP configurations) (since 9.0) 51''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 52 53Specified CPU topology parameters must be supported by the machine. 54 55In the SMP configuration, users should provide the CPU topology parameters that 56are supported by the target machine. 57 58However, historically it was allowed for users to specify the unsupported 59topology parameter as "1", which is meaningless. So support for this kind of 60configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is 61marked deprecated since 9.0, users have to ensure that all the topology members 62described with -smp are supported by the target machine. 63 64``-runas`` (since 9.1) 65---------------------- 66 67Use ``-run-with user=..`` instead. 68 69 70User-mode emulator command line arguments 71----------------------------------------- 72 73``-p`` (since 9.0) 74'''''''''''''''''' 75 76The ``-p`` option pretends to control the host page size. However, 77it is not possible to change the host page size, and using the 78option only causes failures. 79 80QEMU Machine Protocol (QMP) commands 81------------------------------------ 82 83``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 84''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 85 86Use argument ``id`` instead. 87 88``eject`` argument ``device`` (since 2.8) 89''''''''''''''''''''''''''''''''''''''''' 90 91Use argument ``id`` instead. 92 93``blockdev-change-medium`` argument ``device`` (since 2.8) 94'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 95 96Use argument ``id`` instead. 97 98``block_set_io_throttle`` argument ``device`` (since 2.8) 99''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 100 101Use argument ``id`` instead. 102 103``blockdev-add`` empty string argument ``backing`` (since 2.10) 104''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 105 106Use argument value ``null`` instead. 107 108``block-commit`` arguments ``base`` and ``top`` (since 3.1) 109''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 110 111Use arguments ``base-node`` and ``top-node`` instead. 112 113``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 114'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 115 116Use the more generic commands ``block-export-add`` and ``block-export-del`` 117instead. As part of this deprecation, where ``nbd-server-add`` used a 118single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 119 120``query-qmp-schema`` return value member ``values`` (since 6.2) 121''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 122 123Member ``values`` in return value elements with meta-type ``enum`` is 124deprecated. Use ``members`` instead. 125 126``drive-backup`` (since 6.2) 127'''''''''''''''''''''''''''' 128 129Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 130This change primarily separates the creation/opening process of the backup 131target with explicit, separate steps. ``blockdev-backup`` uses mostly the 132same arguments as ``drive-backup``, except the ``format`` and ``mode`` 133options are removed in favor of using explicit ``blockdev-create`` and 134``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 135details. 136 137Incorrectly typed ``device_add`` arguments (since 6.2) 138'''''''''''''''''''''''''''''''''''''''''''''''''''''' 139 140Due to shortcomings in the internal implementation of ``device_add``, QEMU 141incorrectly accepts certain invalid arguments: Any object or list arguments are 142silently ignored. Other argument types are not checked, but an implicit 143conversion happens, so that e.g. string values can be assigned to integer 144device properties or vice versa. 145 146This is a bug in QEMU that will be fixed in the future so that previously 147accepted incorrect commands will return an error. Users should make sure that 148all arguments passed to ``device_add`` are consistent with the documented 149property types. 150 151QEMU Machine Protocol (QMP) events 152---------------------------------- 153 154``vcpu`` trace events (since 8.1) 155''''''''''''''''''''''''''''''''' 156 157The ability to instrument QEMU helper functions with vCPU-aware trace 158points was removed in 7.0. However QMP still exposed the vcpu 159parameter. This argument has now been deprecated and the remaining 160remaining trace points that used it are selected just by name. 161 162Host Architectures 163------------------ 164 165BE MIPS (since 7.2) 166''''''''''''''''''' 167 168As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 169MIPS moved out of support making it hard to maintain our 170cross-compilation CI tests of the architecture. As we no longer have 171CI coverage support may bitrot away before the deprecation process 172completes. The little endian variants of MIPS (both 32 and 64 bit) are 173still a supported host architecture. 174 175System emulation on 32-bit x86 hosts (since 8.0) 176'''''''''''''''''''''''''''''''''''''''''''''''' 177 178Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 179OS distributions given the widespread availability of 64-bit x86 hardware. 180The QEMU project no longer considers 32-bit x86 support for system emulation to 181be an effective use of its limited resources, and thus intends to discontinue 182it. Since all recent x86 hardware from the past >10 years is capable of the 18364-bit x86 extensions, a corresponding 64-bit OS should be used instead. 184 185 186System emulator CPUs 187-------------------- 188 189``power5+`` and ``power7+`` CPU names (since 9.0) 190''''''''''''''''''''''''''''''''''''''''''''''''' 191 192The character "+" in device (and thus also CPU) names is not allowed 193in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``, 194``power7+`` and ``power7+_v2.1`` are currently still supported via 195an alias, but for consistency these will get removed in a future 196release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead. 197 198``Sun-UltraSparc-IIIi+`` and ``Sun-UltraSparc-IV+`` CPU names (since 9.1) 199''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 200 201The character "+" in device (and thus also CPU) names is not allowed 202in the QEMU object model anymore. ``Sun-UltraSparc-IIIi+`` and 203``Sun-UltraSparc-IV+`` are currently still supported via a workaround, 204but for consistency these will get removed in a future release, too. 205Use ``Sun-UltraSparc-IIIi-plus`` and ``Sun-UltraSparc-IV-plus`` instead. 206 207CRIS CPU architecture (since 9.0) 208''''''''''''''''''''''''''''''''' 209 210The CRIS architecture was pulled from Linux in 4.17 and the compiler 211is no longer packaged in any distro making it harder to run the 212``check-tcg`` tests. Unless we can improve the testing situation there 213is a chance the code will bitrot without anyone noticing. 214 215System emulator machines 216------------------------ 217 218Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 219'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 220 221The ``dtb-kaslr-seed`` property on the ``virt`` board has been 222deprecated; use the new name ``dtb-randomness`` instead. The new name 223better reflects the way this property affects all random data within 224the device tree blob, not just the ``kaslr-seed`` node. 225 226``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2) 227''''''''''''''''''''''''''''''''''''''''''''''''''''' 228 229These old machine types are quite neglected nowadays and thus might have 230various pitfalls with regards to live migration. Use a newer machine type 231instead. 232 233``shix`` (since 9.0) 234'''''''''''''''''''' 235 236The machine is no longer in existence and has been long unmaintained 237in QEMU. This also holds for the TC51828 16MiB flash that it uses. 238 239``pseries-2.1`` up to ``pseries-2.12`` (since 9.0) 240'''''''''''''''''''''''''''''''''''''''''''''''''' 241 242Older pseries machines before version 3.0 have undergone many changes 243to correct issues, mostly regarding migration compatibility. These are 244no longer maintained and removing them will make the code easier to 245read and maintain. Use versions 3.0 and above as a replacement. 246 247Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0) 248'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 249 250QEMU includes models of some machine types where the QEMU code that 251emulates their SoCs is very old and unmaintained. This code is now 252blocking our ability to move forward with various changes across 253the codebase, and over many years nobody has been interested in 254trying to modernise it. We don't expect any of these machines to have 255a large number of users, because they're all modelling hardware that 256has now passed away into history. We are therefore dropping support 257for all machine types using the PXA2xx and OMAP2 SoCs. We are also 258dropping the ``cheetah`` OMAP1 board, because we don't have any 259test images for it and don't know of anybody who does; the ``sx1`` 260and ``sx1-v1`` OMAP1 machines remain supported for now. 261 262PPC 405 ``ref405ep`` machine (since 9.1) 263'''''''''''''''''''''''''''''''''''''''' 264 265The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware 266images are not available, OpenWRT dropped support in 2019, U-Boot in 2672017, Linux also is dropping support in 2024. It is time to let go of 268this ancient hardware and focus on newer CPUs and platforms. 269 270Backend options 271--------------- 272 273Using non-persistent backing file with pmem=on (since 6.1) 274'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 275 276This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 277device. However enabling ``memory-backend-file.pmem`` option, when backing file 278is (a) not DAX capable or (b) not on a filesystem that support direct mapping 279of persistent memory, is not safe and may lead to data loss or corruption in case 280of host crash. 281Options are: 282 283 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 284 (without persistence guaranties) with backing file on non DAX storage 285 - move backing file to NVDIMM storage and keep ``pmem=on`` 286 (to have NVDIMM with persistence guaranties). 287 288Device options 289-------------- 290 291Emulated device options 292''''''''''''''''''''''' 293 294``-device virtio-blk,scsi=on|off`` (since 5.0) 295^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 296 297The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 298and later do not support it because the virtio-scsi device was introduced for 299full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 300 301Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 302alias. 303 304``-device nvme-ns,eui64-default=on|off`` (since 7.1) 305^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 306 307In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 308identifier that is not globally unique. If an EUI-64 identifier is required, the 309user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 310 311``-device nvme,use-intel-id=on|off`` (since 7.1) 312^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 313 314The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 315from Intel that was not properly allocated. Since version 5.2, the controller 316has used a properly allocated identifier. Deprecate the ``use-intel-id`` 317machine compatibility parameter. 318 319``-device cxl-type3,memdev=xxxx`` (since 8.0) 320^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 321 322The ``cxl-type3`` device initially only used a single memory backend. With 323the addition of volatile memory support, it is now necessary to distinguish 324between persistent and volatile memory backends. As such, memdev is deprecated 325in favor of persistent-memdev. 326 327``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 328^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 329 330The 9p ``proxy`` filesystem backend driver has been deprecated and will be 331removed (along with its proxy helper daemon) in a future version of QEMU. Please 332use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 333backend, or alternatively consider deploying virtiofsd instead. 334 335The 9p ``proxy`` backend was originally developed as an alternative to the 9p 336``local`` backend. The idea was to enhance security by dispatching actual low 337level filesystem operations from 9p server (QEMU process) over to a separate 338process (the virtfs-proxy-helper binary). However this alternative never gained 339momentum. The proxy backend is much slower than the local backend, hasn't seen 340any development in years, and showed to be less secure, especially due to the 341fact that its helper daemon must be run as root, whereas with the local backend 342QEMU is typically run as unprivileged user and allows to tighten behaviour by 343mapping permissions et al by using its 'mapped' security model option. 344 345Nowadays it would make sense to reimplement the ``proxy`` backend by using 346QEMU's ``vhost`` feature, which would eliminate the high latency costs under 347which the 9p ``proxy`` backend currently suffers. However as of to date nobody 348has indicated plans for such kind of reimplementation unfortunately. 349 350RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 351^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 352 353The 'any' CPU type was introduced back in 2018 and has been around since the 354initial RISC-V QEMU port. Its usage has always been unclear: users don't know 355what to expect from a CPU called 'any', and in fact the CPU does not do anything 356special that isn't already done by the default CPUs rv32/rv64. 357 358After the introduction of the 'max' CPU type, RISC-V now has a good coverage 359of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 360CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 361CPU type starting in 8.2. 362 363RISC-V CPU properties which start with capital 'Z' (since 8.2) 364^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 365 366All RISC-V CPU properties which start with capital 'Z' are being deprecated 367starting in 8.2. The reason is that they were wrongly added with capital 'Z' 368in the past. CPU properties were later added with lower-case names, which 369is the format we want to use from now on. 370 371Users which try to use these deprecated properties will receive a warning 372recommending to switch to their stable counterparts: 373 374- "Zifencei" should be replaced with "zifencei" 375- "Zicsr" should be replaced with "zicsr" 376- "Zihintntl" should be replaced with "zihintntl" 377- "Zihintpause" should be replaced with "zihintpause" 378- "Zawrs" should be replaced with "zawrs" 379- "Zfa" should be replaced with "zfa" 380- "Zfh" should be replaced with "zfh" 381- "Zfhmin" should be replaced with "zfhmin" 382- "Zve32f" should be replaced with "zve32f" 383- "Zve64f" should be replaced with "zve64f" 384- "Zve64d" should be replaced with "zve64d" 385 386Block device options 387'''''''''''''''''''' 388 389``"backing": ""`` (since 2.12) 390^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 391 392In order to prevent QEMU from automatically opening an image's backing 393chain, use ``"backing": null`` instead. 394 395``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 396^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 397 398Options for ``rbd`` should be specified according to its runtime options, 399like other block drivers. Legacy parsing of keyvalue pair encoded 400filenames is useful to open images with the old format for backing files; 401These image files should be updated to use the current format. 402 403Example of legacy encoding:: 404 405 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 406 407The above, converted to the current supported format:: 408 409 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 410 411``iscsi,password=xxx`` (since 8.0) 412^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 413 414Specifying the iSCSI password in plain text on the command line using the 415``password`` option is insecure. The ``password-secret`` option should be 416used instead, to refer to a ``--object secret...`` instance that provides 417a password via a file, or encrypted. 418 419Character device options 420'''''''''''''''''''''''' 421 422Backend ``memory`` (since 9.0) 423^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 424 425``memory`` is a deprecated synonym for ``ringbuf``. 426 427CPU device properties 428''''''''''''''''''''' 429 430``pcommit`` on x86 (since 9.1) 431^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 432 433The PCOMMIT instruction was never included in any physical processor. 434It was implemented as a no-op instruction in TCG up to QEMU 9.0, but 435only with ``-cpu max`` (which does not guarantee migration compatibility 436across versions). 437 438``pmu-num=n`` on RISC-V CPUs (since 8.2) 439^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 440 441In order to support more flexible counter configurations this has been replaced 442by a ``pmu-mask`` property. If set of counters is continuous then the mask can 443be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 444must be left clear. 445 446 447Backwards compatibility 448----------------------- 449 450Runnability guarantee of CPU models (since 4.1) 451''''''''''''''''''''''''''''''''''''''''''''''' 452 453Previous versions of QEMU never changed existing CPU models in 454ways that introduced additional host software or hardware 455requirements to the VM. This allowed management software to 456safely change the machine type of an existing VM without 457introducing new requirements ("runnability guarantee"). This 458prevented CPU models from being updated to include CPU 459vulnerability mitigations, leaving guests vulnerable in the 460default configuration. 461 462The CPU model runnability guarantee won't apply anymore to 463existing CPU models. Management software that needs runnability 464guarantees must resolve the CPU model aliases using the 465``alias-of`` field returned by the ``query-cpu-definitions`` QMP 466command. 467 468While those guarantees are kept, the return value of 469``query-cpu-definitions`` will have existing CPU model aliases 470point to a version that doesn't break runnability guarantees 471(specifically, version 1 of those CPU models). In future QEMU 472versions, aliases will point to newer CPU model versions 473depending on the machine type, so management software must 474resolve CPU model aliases before starting a virtual machine. 475 476QEMU guest agent 477---------------- 478 479``--blacklist`` command line option (since 7.2) 480''''''''''''''''''''''''''''''''''''''''''''''' 481 482``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 483wording for what this option does). The short form ``-b`` still stays 484the same and thus is the preferred way for scripts that should run with 485both, older and future versions of QEMU. 486 487``blacklist`` config file option (since 7.2) 488'''''''''''''''''''''''''''''''''''''''''''' 489 490The ``blacklist`` config file option has been renamed to ``block-rpcs`` 491(to be in sync with the renaming of the corresponding command line 492option). 493 494Migration 495--------- 496 497``fd:`` URI when used for file migration (since 9.1) 498'''''''''''''''''''''''''''''''''''''''''''''''''''' 499 500The ``fd:`` URI can currently provide a file descriptor that 501references either a socket or a plain file. These are two different 502types of migration. In order to reduce ambiguity, the ``fd:`` URI 503usage of providing a file descriptor to a plain file has been 504deprecated in favor of explicitly using the ``file:`` URI with the 505file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` 506command documentation for details on the ``fdset`` usage. 507