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 151Host Architectures 152------------------ 153 154BE MIPS (since 7.2) 155''''''''''''''''''' 156 157As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 158MIPS moved out of support making it hard to maintain our 159cross-compilation CI tests of the architecture. As we no longer have 160CI coverage support may bitrot away before the deprecation process 161completes. The little endian variants of MIPS (both 32 and 64 bit) are 162still a supported host architecture. 163 164System emulation on 32-bit x86 hosts (since 8.0) 165'''''''''''''''''''''''''''''''''''''''''''''''' 166 167Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 168OS distributions given the widespread availability of 64-bit x86 hardware. 169The QEMU project no longer considers 32-bit x86 support for system emulation to 170be an effective use of its limited resources, and thus intends to discontinue 171it. Since all recent x86 hardware from the past >10 years is capable of the 17264-bit x86 extensions, a corresponding 64-bit OS should be used instead. 173 174 175System emulator CPUs 176-------------------- 177 178``power5+`` and ``power7+`` CPU names (since 9.0) 179''''''''''''''''''''''''''''''''''''''''''''''''' 180 181The character "+" in device (and thus also CPU) names is not allowed 182in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``, 183``power7+`` and ``power7+_v2.1`` are currently still supported via 184an alias, but for consistency these will get removed in a future 185release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead. 186 187``Sun-UltraSparc-IIIi+`` and ``Sun-UltraSparc-IV+`` CPU names (since 9.1) 188''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 189 190The character "+" in device (and thus also CPU) names is not allowed 191in the QEMU object model anymore. ``Sun-UltraSparc-IIIi+`` and 192``Sun-UltraSparc-IV+`` are currently still supported via a workaround, 193but for consistency these will get removed in a future release, too. 194Use ``Sun-UltraSparc-IIIi-plus`` and ``Sun-UltraSparc-IV-plus`` instead. 195 196CRIS CPU architecture (since 9.0) 197''''''''''''''''''''''''''''''''' 198 199The CRIS architecture was pulled from Linux in 4.17 and the compiler 200is no longer packaged in any distro making it harder to run the 201``check-tcg`` tests. Unless we can improve the testing situation there 202is a chance the code will bitrot without anyone noticing. 203 204System emulator machines 205------------------------ 206 207Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 208'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 209 210The ``dtb-kaslr-seed`` property on the ``virt`` board has been 211deprecated; use the new name ``dtb-randomness`` instead. The new name 212better reflects the way this property affects all random data within 213the device tree blob, not just the ``kaslr-seed`` node. 214 215``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2) 216''''''''''''''''''''''''''''''''''''''''''''''''''''' 217 218These old machine types are quite neglected nowadays and thus might have 219various pitfalls with regards to live migration. Use a newer machine type 220instead. 221 222``shix`` (since 9.0) 223'''''''''''''''''''' 224 225The machine is no longer in existence and has been long unmaintained 226in QEMU. This also holds for the TC51828 16MiB flash that it uses. 227 228``pseries-2.1`` up to ``pseries-2.12`` (since 9.0) 229'''''''''''''''''''''''''''''''''''''''''''''''''' 230 231Older pseries machines before version 3.0 have undergone many changes 232to correct issues, mostly regarding migration compatibility. These are 233no longer maintained and removing them will make the code easier to 234read and maintain. Use versions 3.0 and above as a replacement. 235 236Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0) 237'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 238 239QEMU includes models of some machine types where the QEMU code that 240emulates their SoCs is very old and unmaintained. This code is now 241blocking our ability to move forward with various changes across 242the codebase, and over many years nobody has been interested in 243trying to modernise it. We don't expect any of these machines to have 244a large number of users, because they're all modelling hardware that 245has now passed away into history. We are therefore dropping support 246for all machine types using the PXA2xx and OMAP2 SoCs. We are also 247dropping the ``cheetah`` OMAP1 board, because we don't have any 248test images for it and don't know of anybody who does; the ``sx1`` 249and ``sx1-v1`` OMAP1 machines remain supported for now. 250 251PPC 405 ``ref405ep`` machine (since 9.1) 252'''''''''''''''''''''''''''''''''''''''' 253 254The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware 255images are not available, OpenWRT dropped support in 2019, U-Boot in 2562017, Linux also is dropping support in 2024. It is time to let go of 257this ancient hardware and focus on newer CPUs and platforms. 258 259Backend options 260--------------- 261 262Using non-persistent backing file with pmem=on (since 6.1) 263'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 264 265This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 266device. However enabling ``memory-backend-file.pmem`` option, when backing file 267is (a) not DAX capable or (b) not on a filesystem that support direct mapping 268of persistent memory, is not safe and may lead to data loss or corruption in case 269of host crash. 270Options are: 271 272 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 273 (without persistence guaranties) with backing file on non DAX storage 274 - move backing file to NVDIMM storage and keep ``pmem=on`` 275 (to have NVDIMM with persistence guaranties). 276 277Device options 278-------------- 279 280Emulated device options 281''''''''''''''''''''''' 282 283``-device virtio-blk,scsi=on|off`` (since 5.0) 284^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 285 286The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 287and later do not support it because the virtio-scsi device was introduced for 288full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 289 290Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 291alias. 292 293``-device nvme-ns,eui64-default=on|off`` (since 7.1) 294^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 295 296In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 297identifier that is not globally unique. If an EUI-64 identifier is required, the 298user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 299 300``-device nvme,use-intel-id=on|off`` (since 7.1) 301^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 302 303The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 304from Intel that was not properly allocated. Since version 5.2, the controller 305has used a properly allocated identifier. Deprecate the ``use-intel-id`` 306machine compatibility parameter. 307 308``-device cxl-type3,memdev=xxxx`` (since 8.0) 309^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 310 311The ``cxl-type3`` device initially only used a single memory backend. With 312the addition of volatile memory support, it is now necessary to distinguish 313between persistent and volatile memory backends. As such, memdev is deprecated 314in favor of persistent-memdev. 315 316``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 317^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 318 319The 9p ``proxy`` filesystem backend driver has been deprecated and will be 320removed (along with its proxy helper daemon) in a future version of QEMU. Please 321use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 322backend, or alternatively consider deploying virtiofsd instead. 323 324The 9p ``proxy`` backend was originally developed as an alternative to the 9p 325``local`` backend. The idea was to enhance security by dispatching actual low 326level filesystem operations from 9p server (QEMU process) over to a separate 327process (the virtfs-proxy-helper binary). However this alternative never gained 328momentum. The proxy backend is much slower than the local backend, hasn't seen 329any development in years, and showed to be less secure, especially due to the 330fact that its helper daemon must be run as root, whereas with the local backend 331QEMU is typically run as unprivileged user and allows to tighten behaviour by 332mapping permissions et al by using its 'mapped' security model option. 333 334Nowadays it would make sense to reimplement the ``proxy`` backend by using 335QEMU's ``vhost`` feature, which would eliminate the high latency costs under 336which the 9p ``proxy`` backend currently suffers. However as of to date nobody 337has indicated plans for such kind of reimplementation unfortunately. 338 339RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 340^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 341 342The 'any' CPU type was introduced back in 2018 and has been around since the 343initial RISC-V QEMU port. Its usage has always been unclear: users don't know 344what to expect from a CPU called 'any', and in fact the CPU does not do anything 345special that isn't already done by the default CPUs rv32/rv64. 346 347After the introduction of the 'max' CPU type, RISC-V now has a good coverage 348of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 349CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 350CPU type starting in 8.2. 351 352RISC-V CPU properties which start with capital 'Z' (since 8.2) 353^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 354 355All RISC-V CPU properties which start with capital 'Z' are being deprecated 356starting in 8.2. The reason is that they were wrongly added with capital 'Z' 357in the past. CPU properties were later added with lower-case names, which 358is the format we want to use from now on. 359 360Users which try to use these deprecated properties will receive a warning 361recommending to switch to their stable counterparts: 362 363- "Zifencei" should be replaced with "zifencei" 364- "Zicsr" should be replaced with "zicsr" 365- "Zihintntl" should be replaced with "zihintntl" 366- "Zihintpause" should be replaced with "zihintpause" 367- "Zawrs" should be replaced with "zawrs" 368- "Zfa" should be replaced with "zfa" 369- "Zfh" should be replaced with "zfh" 370- "Zfhmin" should be replaced with "zfhmin" 371- "Zve32f" should be replaced with "zve32f" 372- "Zve64f" should be replaced with "zve64f" 373- "Zve64d" should be replaced with "zve64d" 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 408Character device options 409'''''''''''''''''''''''' 410 411Backend ``memory`` (since 9.0) 412^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 413 414``memory`` is a deprecated synonym for ``ringbuf``. 415 416CPU device properties 417''''''''''''''''''''' 418 419``pcommit`` on x86 (since 9.1) 420^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 421 422The PCOMMIT instruction was never included in any physical processor. 423It was implemented as a no-op instruction in TCG up to QEMU 9.0, but 424only with ``-cpu max`` (which does not guarantee migration compatibility 425across versions). 426 427``pmu-num=n`` on RISC-V CPUs (since 8.2) 428^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 429 430In order to support more flexible counter configurations this has been replaced 431by a ``pmu-mask`` property. If set of counters is continuous then the mask can 432be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 433must be left clear. 434 435 436Backwards compatibility 437----------------------- 438 439Runnability guarantee of CPU models (since 4.1) 440''''''''''''''''''''''''''''''''''''''''''''''' 441 442Previous versions of QEMU never changed existing CPU models in 443ways that introduced additional host software or hardware 444requirements to the VM. This allowed management software to 445safely change the machine type of an existing VM without 446introducing new requirements ("runnability guarantee"). This 447prevented CPU models from being updated to include CPU 448vulnerability mitigations, leaving guests vulnerable in the 449default configuration. 450 451The CPU model runnability guarantee won't apply anymore to 452existing CPU models. Management software that needs runnability 453guarantees must resolve the CPU model aliases using the 454``alias-of`` field returned by the ``query-cpu-definitions`` QMP 455command. 456 457While those guarantees are kept, the return value of 458``query-cpu-definitions`` will have existing CPU model aliases 459point to a version that doesn't break runnability guarantees 460(specifically, version 1 of those CPU models). In future QEMU 461versions, aliases will point to newer CPU model versions 462depending on the machine type, so management software must 463resolve CPU model aliases before starting a virtual machine. 464 465QEMU guest agent 466---------------- 467 468``--blacklist`` command line option (since 7.2) 469''''''''''''''''''''''''''''''''''''''''''''''' 470 471``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 472wording for what this option does). The short form ``-b`` still stays 473the same and thus is the preferred way for scripts that should run with 474both, older and future versions of QEMU. 475 476``blacklist`` config file option (since 7.2) 477'''''''''''''''''''''''''''''''''''''''''''' 478 479The ``blacklist`` config file option has been renamed to ``block-rpcs`` 480(to be in sync with the renaming of the corresponding command line 481option). 482 483Migration 484--------- 485 486``fd:`` URI when used for file migration (since 9.1) 487'''''''''''''''''''''''''''''''''''''''''''''''''''' 488 489The ``fd:`` URI can currently provide a file descriptor that 490references either a socket or a plain file. These are two different 491types of migration. In order to reduce ambiguity, the ``fd:`` URI 492usage of providing a file descriptor to a plain file has been 493deprecated in favor of explicitly using the ``file:`` URI with the 494file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` 495command documentation for details on the ``fdset`` usage. 496