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 64User-mode emulator command line arguments 65----------------------------------------- 66 67``-p`` (since 9.0) 68'''''''''''''''''' 69 70The ``-p`` option pretends to control the host page size. However, 71it is not possible to change the host page size, and using the 72option only causes failures. 73 74QEMU Machine Protocol (QMP) commands 75------------------------------------ 76 77``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 78''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 79 80Use argument ``id`` instead. 81 82``eject`` argument ``device`` (since 2.8) 83''''''''''''''''''''''''''''''''''''''''' 84 85Use argument ``id`` instead. 86 87``blockdev-change-medium`` argument ``device`` (since 2.8) 88'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 89 90Use argument ``id`` instead. 91 92``block_set_io_throttle`` argument ``device`` (since 2.8) 93''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 94 95Use argument ``id`` instead. 96 97``blockdev-add`` empty string argument ``backing`` (since 2.10) 98''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 99 100Use argument value ``null`` instead. 101 102``block-commit`` arguments ``base`` and ``top`` (since 3.1) 103''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 104 105Use arguments ``base-node`` and ``top-node`` instead. 106 107``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 108'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 109 110Use the more generic commands ``block-export-add`` and ``block-export-del`` 111instead. As part of this deprecation, where ``nbd-server-add`` used a 112single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 113 114``query-qmp-schema`` return value member ``values`` (since 6.2) 115''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 116 117Member ``values`` in return value elements with meta-type ``enum`` is 118deprecated. Use ``members`` instead. 119 120``drive-backup`` (since 6.2) 121'''''''''''''''''''''''''''' 122 123Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 124This change primarily separates the creation/opening process of the backup 125target with explicit, separate steps. ``blockdev-backup`` uses mostly the 126same arguments as ``drive-backup``, except the ``format`` and ``mode`` 127options are removed in favor of using explicit ``blockdev-create`` and 128``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 129details. 130 131Incorrectly typed ``device_add`` arguments (since 6.2) 132'''''''''''''''''''''''''''''''''''''''''''''''''''''' 133 134Due to shortcomings in the internal implementation of ``device_add``, QEMU 135incorrectly accepts certain invalid arguments: Any object or list arguments are 136silently ignored. Other argument types are not checked, but an implicit 137conversion happens, so that e.g. string values can be assigned to integer 138device properties or vice versa. 139 140This is a bug in QEMU that will be fixed in the future so that previously 141accepted incorrect commands will return an error. Users should make sure that 142all arguments passed to ``device_add`` are consistent with the documented 143property types. 144 145QEMU Machine Protocol (QMP) events 146---------------------------------- 147 148``MEM_UNPLUG_ERROR`` (since 6.2) 149'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 150 151Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead. 152 153``vcpu`` trace events (since 8.1) 154''''''''''''''''''''''''''''''''' 155 156The ability to instrument QEMU helper functions with vCPU-aware trace 157points was removed in 7.0. However QMP still exposed the vcpu 158parameter. This argument has now been deprecated and the remaining 159remaining trace points that used it are selected just by name. 160 161Host Architectures 162------------------ 163 164BE MIPS (since 7.2) 165''''''''''''''''''' 166 167As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 168MIPS moved out of support making it hard to maintain our 169cross-compilation CI tests of the architecture. As we no longer have 170CI coverage support may bitrot away before the deprecation process 171completes. The little endian variants of MIPS (both 32 and 64 bit) are 172still a supported host architecture. 173 174System emulation on 32-bit x86 hosts (since 8.0) 175'''''''''''''''''''''''''''''''''''''''''''''''' 176 177Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 178OS distributions given the widespread availability of 64-bit x86 hardware. 179The QEMU project no longer considers 32-bit x86 support for system emulation to 180be an effective use of its limited resources, and thus intends to discontinue 181it. Since all recent x86 hardware from the past >10 years is capable of the 18264-bit x86 extensions, a corresponding 64-bit OS should be used instead. 183 184 185System emulator CPUs 186-------------------- 187 188``power5+`` and ``power7+`` CPU names (since 9.0) 189''''''''''''''''''''''''''''''''''''''''''''''''' 190 191The character "+" in device (and thus also CPU) names is not allowed 192in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``, 193``power7+`` and ``power7+_v2.1`` are currently still supported via 194an alias, but for consistency these will get removed in a future 195release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead. 196 197``Sun-UltraSparc-IIIi+`` and ``Sun-UltraSparc-IV+`` CPU names (since 9.1) 198''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 199 200The character "+" in device (and thus also CPU) names is not allowed 201in the QEMU object model anymore. ``Sun-UltraSparc-IIIi+`` and 202``Sun-UltraSparc-IV+`` are currently still supported via a workaround, 203but for consistency these will get removed in a future release, too. 204Use ``Sun-UltraSparc-IIIi-plus`` and ``Sun-UltraSparc-IV-plus`` instead. 205 206CRIS CPU architecture (since 9.0) 207''''''''''''''''''''''''''''''''' 208 209The CRIS architecture was pulled from Linux in 4.17 and the compiler 210is no longer packaged in any distro making it harder to run the 211``check-tcg`` tests. Unless we can improve the testing situation there 212is a chance the code will bitrot without anyone noticing. 213 214System emulator machines 215------------------------ 216 217Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 218'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 219 220The ``dtb-kaslr-seed`` property on the ``virt`` board has been 221deprecated; use the new name ``dtb-randomness`` instead. The new name 222better reflects the way this property affects all random data within 223the device tree blob, not just the ``kaslr-seed`` node. 224 225``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2) 226''''''''''''''''''''''''''''''''''''''''''''''''''''' 227 228These old machine types are quite neglected nowadays and thus might have 229various pitfalls with regards to live migration. Use a newer machine type 230instead. 231 232``shix`` (since 9.0) 233'''''''''''''''''''' 234 235The machine is no longer in existence and has been long unmaintained 236in QEMU. This also holds for the TC51828 16MiB flash that it uses. 237 238``pseries-2.1`` up to ``pseries-2.12`` (since 9.0) 239'''''''''''''''''''''''''''''''''''''''''''''''''' 240 241Older pseries machines before version 3.0 have undergone many changes 242to correct issues, mostly regarding migration compatibility. These are 243no longer maintained and removing them will make the code easier to 244read and maintain. Use versions 3.0 and above as a replacement. 245 246Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0) 247'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 248 249QEMU includes models of some machine types where the QEMU code that 250emulates their SoCs is very old and unmaintained. This code is now 251blocking our ability to move forward with various changes across 252the codebase, and over many years nobody has been interested in 253trying to modernise it. We don't expect any of these machines to have 254a large number of users, because they're all modelling hardware that 255has now passed away into history. We are therefore dropping support 256for all machine types using the PXA2xx and OMAP2 SoCs. We are also 257dropping the ``cheetah`` OMAP1 board, because we don't have any 258test images for it and don't know of anybody who does; the ``sx1`` 259and ``sx1-v1`` OMAP1 machines remain supported for now. 260 261PPC 405 ``ref405ep`` machine (since 9.1) 262'''''''''''''''''''''''''''''''''''''''' 263 264The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware 265images are not available, OpenWRT dropped support in 2019, U-Boot in 2662017, Linux also is dropping support in 2024. It is time to let go of 267this ancient hardware and focus on newer CPUs and platforms. 268 269Backend options 270--------------- 271 272Using non-persistent backing file with pmem=on (since 6.1) 273'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 274 275This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 276device. However enabling ``memory-backend-file.pmem`` option, when backing file 277is (a) not DAX capable or (b) not on a filesystem that support direct mapping 278of persistent memory, is not safe and may lead to data loss or corruption in case 279of host crash. 280Options are: 281 282 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 283 (without persistence guaranties) with backing file on non DAX storage 284 - move backing file to NVDIMM storage and keep ``pmem=on`` 285 (to have NVDIMM with persistence guaranties). 286 287Device options 288-------------- 289 290Emulated device options 291''''''''''''''''''''''' 292 293``-device virtio-blk,scsi=on|off`` (since 5.0) 294^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 295 296The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 297and later do not support it because the virtio-scsi device was introduced for 298full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 299 300Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 301alias. 302 303``-device nvme-ns,eui64-default=on|off`` (since 7.1) 304^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 305 306In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 307identifier that is not globally unique. If an EUI-64 identifier is required, the 308user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 309 310``-device nvme,use-intel-id=on|off`` (since 7.1) 311^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 312 313The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 314from Intel that was not properly allocated. Since version 5.2, the controller 315has used a properly allocated identifier. Deprecate the ``use-intel-id`` 316machine compatibility parameter. 317 318``-device cxl-type3,memdev=xxxx`` (since 8.0) 319^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 320 321The ``cxl-type3`` device initially only used a single memory backend. With 322the addition of volatile memory support, it is now necessary to distinguish 323between persistent and volatile memory backends. As such, memdev is deprecated 324in favor of persistent-memdev. 325 326``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 327^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 328 329The 9p ``proxy`` filesystem backend driver has been deprecated and will be 330removed (along with its proxy helper daemon) in a future version of QEMU. Please 331use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 332backend, or alternatively consider deploying virtiofsd instead. 333 334The 9p ``proxy`` backend was originally developed as an alternative to the 9p 335``local`` backend. The idea was to enhance security by dispatching actual low 336level filesystem operations from 9p server (QEMU process) over to a separate 337process (the virtfs-proxy-helper binary). However this alternative never gained 338momentum. The proxy backend is much slower than the local backend, hasn't seen 339any development in years, and showed to be less secure, especially due to the 340fact that its helper daemon must be run as root, whereas with the local backend 341QEMU is typically run as unprivileged user and allows to tighten behaviour by 342mapping permissions et al by using its 'mapped' security model option. 343 344Nowadays it would make sense to reimplement the ``proxy`` backend by using 345QEMU's ``vhost`` feature, which would eliminate the high latency costs under 346which the 9p ``proxy`` backend currently suffers. However as of to date nobody 347has indicated plans for such kind of reimplementation unfortunately. 348 349RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 350^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 351 352The 'any' CPU type was introduced back in 2018 and has been around since the 353initial RISC-V QEMU port. Its usage has always been unclear: users don't know 354what to expect from a CPU called 'any', and in fact the CPU does not do anything 355special that isn't already done by the default CPUs rv32/rv64. 356 357After the introduction of the 'max' CPU type, RISC-V now has a good coverage 358of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 359CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 360CPU type starting in 8.2. 361 362RISC-V CPU properties which start with capital 'Z' (since 8.2) 363^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 364 365All RISC-V CPU properties which start with capital 'Z' are being deprecated 366starting in 8.2. The reason is that they were wrongly added with capital 'Z' 367in the past. CPU properties were later added with lower-case names, which 368is the format we want to use from now on. 369 370Users which try to use these deprecated properties will receive a warning 371recommending to switch to their stable counterparts: 372 373- "Zifencei" should be replaced with "zifencei" 374- "Zicsr" should be replaced with "zicsr" 375- "Zihintntl" should be replaced with "zihintntl" 376- "Zihintpause" should be replaced with "zihintpause" 377- "Zawrs" should be replaced with "zawrs" 378- "Zfa" should be replaced with "zfa" 379- "Zfh" should be replaced with "zfh" 380- "Zfhmin" should be replaced with "zfhmin" 381- "Zve32f" should be replaced with "zve32f" 382- "Zve64f" should be replaced with "zve64f" 383- "Zve64d" should be replaced with "zve64d" 384 385Block device options 386'''''''''''''''''''' 387 388``"backing": ""`` (since 2.12) 389^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 390 391In order to prevent QEMU from automatically opening an image's backing 392chain, use ``"backing": null`` instead. 393 394``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 395^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 396 397Options for ``rbd`` should be specified according to its runtime options, 398like other block drivers. Legacy parsing of keyvalue pair encoded 399filenames is useful to open images with the old format for backing files; 400These image files should be updated to use the current format. 401 402Example of legacy encoding:: 403 404 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 405 406The above, converted to the current supported format:: 407 408 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 409 410``iscsi,password=xxx`` (since 8.0) 411^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 412 413Specifying the iSCSI password in plain text on the command line using the 414``password`` option is insecure. The ``password-secret`` option should be 415used instead, to refer to a ``--object secret...`` instance that provides 416a password via a file, or encrypted. 417 418Character device options 419'''''''''''''''''''''''' 420 421Backend ``memory`` (since 9.0) 422^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 423 424``memory`` is a deprecated synonym for ``ringbuf``. 425 426CPU device properties 427''''''''''''''''''''' 428 429``pmu-num=n`` on RISC-V CPUs (since 8.2) 430^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 431 432In order to support more flexible counter configurations this has been replaced 433by a ``pmu-mask`` property. If set of counters is continuous then the mask can 434be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 435must be left clear. 436 437 438Backwards compatibility 439----------------------- 440 441Runnability guarantee of CPU models (since 4.1) 442''''''''''''''''''''''''''''''''''''''''''''''' 443 444Previous versions of QEMU never changed existing CPU models in 445ways that introduced additional host software or hardware 446requirements to the VM. This allowed management software to 447safely change the machine type of an existing VM without 448introducing new requirements ("runnability guarantee"). This 449prevented CPU models from being updated to include CPU 450vulnerability mitigations, leaving guests vulnerable in the 451default configuration. 452 453The CPU model runnability guarantee won't apply anymore to 454existing CPU models. Management software that needs runnability 455guarantees must resolve the CPU model aliases using the 456``alias-of`` field returned by the ``query-cpu-definitions`` QMP 457command. 458 459While those guarantees are kept, the return value of 460``query-cpu-definitions`` will have existing CPU model aliases 461point to a version that doesn't break runnability guarantees 462(specifically, version 1 of those CPU models). In future QEMU 463versions, aliases will point to newer CPU model versions 464depending on the machine type, so management software must 465resolve CPU model aliases before starting a virtual machine. 466 467QEMU guest agent 468---------------- 469 470``--blacklist`` command line option (since 7.2) 471''''''''''''''''''''''''''''''''''''''''''''''' 472 473``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 474wording for what this option does). The short form ``-b`` still stays 475the same and thus is the preferred way for scripts that should run with 476both, older and future versions of QEMU. 477 478``blacklist`` config file option (since 7.2) 479'''''''''''''''''''''''''''''''''''''''''''' 480 481The ``blacklist`` config file option has been renamed to ``block-rpcs`` 482(to be in sync with the renaming of the corresponding command line 483option). 484 485Migration 486--------- 487 488``skipped`` MigrationStats field (since 8.1) 489'''''''''''''''''''''''''''''''''''''''''''' 490 491``skipped`` field in Migration stats has been deprecated. It hasn't 492been used for more than 10 years. 493 494``inc`` migrate command option (since 8.2) 495'''''''''''''''''''''''''''''''''''''''''' 496 497Use blockdev-mirror with NBD instead. 498 499As an intermediate step the ``inc`` functionality can be achieved by 500setting the ``block-incremental`` migration parameter to ``true``. 501But this parameter is also deprecated. 502 503``blk`` migrate command option (since 8.2) 504'''''''''''''''''''''''''''''''''''''''''' 505 506Use blockdev-mirror with NBD instead. 507 508As an intermediate step the ``blk`` functionality can be achieved by 509setting the ``block`` migration capability to ``true``. But this 510capability is also deprecated. 511 512block migration (since 8.2) 513''''''''''''''''''''''''''' 514 515Block migration is too inflexible. It needs to migrate all block 516devices or none. 517 518Please see "QMP invocation for live storage migration with 519``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst 520for a detailed explanation. 521 522old compression method (since 8.2) 523'''''''''''''''''''''''''''''''''' 524 525Compression method fails too much. Too many races. We are going to 526remove it if nobody fixes it. For starters, migration-test 527compression tests are disabled because they fail randomly. If you need 528compression, use multifd compression methods. 529