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