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 188Nios II CPU (since 8.2) 189''''''''''''''''''''''' 190 191The Nios II architecture is orphan. The ``nios2`` guest CPU support is 192deprecated and will be removed in a future version of QEMU. 193 194``power5+`` and ``power7+`` CPU names (since 9.0) 195''''''''''''''''''''''''''''''''''''''''''''''''' 196 197The character "+" in device (and thus also CPU) names is not allowed 198in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``, 199``power7+`` and ``power7+_v2.1`` are currently still supported via 200an alias, but for consistency these will get removed in a future 201release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead. 202 203CRIS CPU architecture (since 9.0) 204''''''''''''''''''''''''''''''''' 205 206The CRIS architecture was pulled from Linux in 4.17 and the compiler 207is no longer packaged in any distro making it harder to run the 208``check-tcg`` tests. Unless we can improve the testing situation there 209is a chance the code will bitrot without anyone noticing. 210 211System emulator machines 212------------------------ 213 214Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 215'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 216 217The ``dtb-kaslr-seed`` property on the ``virt`` board has been 218deprecated; use the new name ``dtb-randomness`` instead. The new name 219better reflects the way this property affects all random data within 220the device tree blob, not just the ``kaslr-seed`` node. 221 222``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2) 223''''''''''''''''''''''''''''''''''''''''''''''''''''' 224 225These old machine types are quite neglected nowadays and thus might have 226various pitfalls with regards to live migration. Use a newer machine type 227instead. 228 229Nios II ``10m50-ghrd`` and ``nios2-generic-nommu`` machines (since 8.2) 230''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 231 232The Nios II architecture is orphan. 233 234``shix`` (since 9.0) 235'''''''''''''''''''' 236 237The machine is no longer in existence and has been long unmaintained 238in QEMU. This also holds for the TC51828 16MiB flash that it uses. 239 240``pseries-2.1`` up to ``pseries-2.12`` (since 9.0) 241'''''''''''''''''''''''''''''''''''''''''''''''''' 242 243Older pseries machines before version 3.0 have undergone many changes 244to correct issues, mostly regarding migration compatibility. These are 245no longer maintained and removing them will make the code easier to 246read and maintain. Use versions 3.0 and above as a replacement. 247 248Arm machines ``akita``, ``borzoi``, ``cheetah``, ``connex``, ``mainstone``, ``n800``, ``n810``, ``spitz``, ``terrier``, ``tosa``, ``verdex``, ``z2`` (since 9.0) 249'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 250 251QEMU includes models of some machine types where the QEMU code that 252emulates their SoCs is very old and unmaintained. This code is now 253blocking our ability to move forward with various changes across 254the codebase, and over many years nobody has been interested in 255trying to modernise it. We don't expect any of these machines to have 256a large number of users, because they're all modelling hardware that 257has now passed away into history. We are therefore dropping support 258for all machine types using the PXA2xx and OMAP2 SoCs. We are also 259dropping the ``cheetah`` OMAP1 board, because we don't have any 260test images for it and don't know of anybody who does; the ``sx1`` 261and ``sx1-v1`` OMAP1 machines remain supported for now. 262 263Backend options 264--------------- 265 266Using non-persistent backing file with pmem=on (since 6.1) 267'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 268 269This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 270device. However enabling ``memory-backend-file.pmem`` option, when backing file 271is (a) not DAX capable or (b) not on a filesystem that support direct mapping 272of persistent memory, is not safe and may lead to data loss or corruption in case 273of host crash. 274Options are: 275 276 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 277 (without persistence guaranties) with backing file on non DAX storage 278 - move backing file to NVDIMM storage and keep ``pmem=on`` 279 (to have NVDIMM with persistence guaranties). 280 281Device options 282-------------- 283 284Emulated device options 285''''''''''''''''''''''' 286 287``-device virtio-blk,scsi=on|off`` (since 5.0) 288^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 289 290The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 291and later do not support it because the virtio-scsi device was introduced for 292full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 293 294Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 295alias. 296 297``-device nvme-ns,eui64-default=on|off`` (since 7.1) 298^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 299 300In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 301identifier that is not globally unique. If an EUI-64 identifier is required, the 302user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 303 304``-device nvme,use-intel-id=on|off`` (since 7.1) 305^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 306 307The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 308from Intel that was not properly allocated. Since version 5.2, the controller 309has used a properly allocated identifier. Deprecate the ``use-intel-id`` 310machine compatibility parameter. 311 312``-device cxl-type3,memdev=xxxx`` (since 8.0) 313^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 314 315The ``cxl-type3`` device initially only used a single memory backend. With 316the addition of volatile memory support, it is now necessary to distinguish 317between persistent and volatile memory backends. As such, memdev is deprecated 318in favor of persistent-memdev. 319 320``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 321^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 322 323The 9p ``proxy`` filesystem backend driver has been deprecated and will be 324removed (along with its proxy helper daemon) in a future version of QEMU. Please 325use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 326backend, or alternatively consider deploying virtiofsd instead. 327 328The 9p ``proxy`` backend was originally developed as an alternative to the 9p 329``local`` backend. The idea was to enhance security by dispatching actual low 330level filesystem operations from 9p server (QEMU process) over to a separate 331process (the virtfs-proxy-helper binary). However this alternative never gained 332momentum. The proxy backend is much slower than the local backend, hasn't seen 333any development in years, and showed to be less secure, especially due to the 334fact that its helper daemon must be run as root, whereas with the local backend 335QEMU is typically run as unprivileged user and allows to tighten behaviour by 336mapping permissions et al by using its 'mapped' security model option. 337 338Nowadays it would make sense to reimplement the ``proxy`` backend by using 339QEMU's ``vhost`` feature, which would eliminate the high latency costs under 340which the 9p ``proxy`` backend currently suffers. However as of to date nobody 341has indicated plans for such kind of reimplementation unfortunately. 342 343RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 344^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 345 346The 'any' CPU type was introduced back in 2018 and has been around since the 347initial RISC-V QEMU port. Its usage has always been unclear: users don't know 348what to expect from a CPU called 'any', and in fact the CPU does not do anything 349special that isn't already done by the default CPUs rv32/rv64. 350 351After the introduction of the 'max' CPU type, RISC-V now has a good coverage 352of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 353CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 354CPU type starting in 8.2. 355 356RISC-V CPU properties which start with capital 'Z' (since 8.2) 357^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 358 359All RISC-V CPU properties which start with capital 'Z' are being deprecated 360starting in 8.2. The reason is that they were wrongly added with capital 'Z' 361in the past. CPU properties were later added with lower-case names, which 362is the format we want to use from now on. 363 364Users which try to use these deprecated properties will receive a warning 365recommending to switch to their stable counterparts: 366 367- "Zifencei" should be replaced with "zifencei" 368- "Zicsr" should be replaced with "zicsr" 369- "Zihintntl" should be replaced with "zihintntl" 370- "Zihintpause" should be replaced with "zihintpause" 371- "Zawrs" should be replaced with "zawrs" 372- "Zfa" should be replaced with "zfa" 373- "Zfh" should be replaced with "zfh" 374- "Zfhmin" should be replaced with "zfhmin" 375- "Zve32f" should be replaced with "zve32f" 376- "Zve64f" should be replaced with "zve64f" 377- "Zve64d" should be replaced with "zve64d" 378 379``-device pvrdma`` and the rdma subsystem (since 8.2) 380^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 381 382The pvrdma device and the whole rdma subsystem are in a bad shape and 383without active maintenance. The QEMU project intends to remove this 384device and subsystem from the code base in a future release without 385replacement unless somebody steps up and improves the situation. 386 387 388Block device options 389'''''''''''''''''''' 390 391``"backing": ""`` (since 2.12) 392^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 393 394In order to prevent QEMU from automatically opening an image's backing 395chain, use ``"backing": null`` instead. 396 397``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 398^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 399 400Options for ``rbd`` should be specified according to its runtime options, 401like other block drivers. Legacy parsing of keyvalue pair encoded 402filenames is useful to open images with the old format for backing files; 403These image files should be updated to use the current format. 404 405Example of legacy encoding:: 406 407 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 408 409The above, converted to the current supported format:: 410 411 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 412 413``iscsi,password=xxx`` (since 8.0) 414^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 415 416Specifying the iSCSI password in plain text on the command line using the 417``password`` option is insecure. The ``password-secret`` option should be 418used instead, to refer to a ``--object secret...`` instance that provides 419a password via a file, or encrypted. 420 421Character device options 422'''''''''''''''''''''''' 423 424Backend ``memory`` (since 9.0) 425^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 426 427``memory`` is a deprecated synonym for ``ringbuf``. 428 429CPU device properties 430''''''''''''''''''''' 431 432``pmu-num=n`` on RISC-V CPUs (since 8.2) 433^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 434 435In order to support more flexible counter configurations this has been replaced 436by a ``pmu-mask`` property. If set of counters is continuous then the mask can 437be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 438must be left clear. 439 440 441Backwards compatibility 442----------------------- 443 444Runnability guarantee of CPU models (since 4.1) 445''''''''''''''''''''''''''''''''''''''''''''''' 446 447Previous versions of QEMU never changed existing CPU models in 448ways that introduced additional host software or hardware 449requirements to the VM. This allowed management software to 450safely change the machine type of an existing VM without 451introducing new requirements ("runnability guarantee"). This 452prevented CPU models from being updated to include CPU 453vulnerability mitigations, leaving guests vulnerable in the 454default configuration. 455 456The CPU model runnability guarantee won't apply anymore to 457existing CPU models. Management software that needs runnability 458guarantees must resolve the CPU model aliases using the 459``alias-of`` field returned by the ``query-cpu-definitions`` QMP 460command. 461 462While those guarantees are kept, the return value of 463``query-cpu-definitions`` will have existing CPU model aliases 464point to a version that doesn't break runnability guarantees 465(specifically, version 1 of those CPU models). In future QEMU 466versions, aliases will point to newer CPU model versions 467depending on the machine type, so management software must 468resolve CPU model aliases before starting a virtual machine. 469 470QEMU guest agent 471---------------- 472 473``--blacklist`` command line option (since 7.2) 474''''''''''''''''''''''''''''''''''''''''''''''' 475 476``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 477wording for what this option does). The short form ``-b`` still stays 478the same and thus is the preferred way for scripts that should run with 479both, older and future versions of QEMU. 480 481``blacklist`` config file option (since 7.2) 482'''''''''''''''''''''''''''''''''''''''''''' 483 484The ``blacklist`` config file option has been renamed to ``block-rpcs`` 485(to be in sync with the renaming of the corresponding command line 486option). 487 488Migration 489--------- 490 491``skipped`` MigrationStats field (since 8.1) 492'''''''''''''''''''''''''''''''''''''''''''' 493 494``skipped`` field in Migration stats has been deprecated. It hasn't 495been used for more than 10 years. 496 497``inc`` migrate command option (since 8.2) 498'''''''''''''''''''''''''''''''''''''''''' 499 500Use blockdev-mirror with NBD instead. 501 502As an intermediate step the ``inc`` functionality can be achieved by 503setting the ``block-incremental`` migration parameter to ``true``. 504But this parameter is also deprecated. 505 506``blk`` migrate command option (since 8.2) 507'''''''''''''''''''''''''''''''''''''''''' 508 509Use blockdev-mirror with NBD instead. 510 511As an intermediate step the ``blk`` functionality can be achieved by 512setting the ``block`` migration capability to ``true``. But this 513capability is also deprecated. 514 515block migration (since 8.2) 516''''''''''''''''''''''''''' 517 518Block migration is too inflexible. It needs to migrate all block 519devices or none. 520 521Please see "QMP invocation for live storage migration with 522``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst 523for a detailed explanation. 524 525old compression method (since 8.2) 526'''''''''''''''''''''''''''''''''' 527 528Compression method fails too much. Too many races. We are going to 529remove it if nobody fixes it. For starters, migration-test 530compression tests are disabled because they fail randomly. If you need 531compression, use multifd compression methods. 532