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 50User-mode emulator command line arguments 51----------------------------------------- 52 53``-p`` (since 9.0) 54'''''''''''''''''' 55 56The ``-p`` option pretends to control the host page size. However, 57it is not possible to change the host page size, and using the 58option only causes failures. 59 60``-smp`` (Unsupported "parameter=1" SMP configurations) (since 9.0) 61''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 62 63Specified CPU topology parameters must be supported by the machine. 64 65In the SMP configuration, users should provide the CPU topology parameters that 66are supported by the target machine. 67 68However, historically it was allowed for users to specify the unsupported 69topology parameter as "1", which is meaningless. So support for this kind of 70configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is 71marked deprecated since 9.0, users have to ensure that all the topology members 72described with -smp are supported by the target machine. 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-2.11`` (since 9.0) 241'''''''''''''''''''''''''''''''''''''''''''''''''' 242 243Older pseries machines before version 2.12 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 2.12 and above as a replacement. 247 248Backend options 249--------------- 250 251Using non-persistent backing file with pmem=on (since 6.1) 252'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 253 254This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 255device. However enabling ``memory-backend-file.pmem`` option, when backing file 256is (a) not DAX capable or (b) not on a filesystem that support direct mapping 257of persistent memory, is not safe and may lead to data loss or corruption in case 258of host crash. 259Options are: 260 261 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 262 (without persistence guaranties) with backing file on non DAX storage 263 - move backing file to NVDIMM storage and keep ``pmem=on`` 264 (to have NVDIMM with persistence guaranties). 265 266Device options 267-------------- 268 269Emulated device options 270''''''''''''''''''''''' 271 272``-device virtio-blk,scsi=on|off`` (since 5.0) 273^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 274 275The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 276and later do not support it because the virtio-scsi device was introduced for 277full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 278 279Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 280alias. 281 282``-device nvme-ns,eui64-default=on|off`` (since 7.1) 283^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 284 285In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 286identifier that is not globally unique. If an EUI-64 identifier is required, the 287user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 288 289``-device nvme,use-intel-id=on|off`` (since 7.1) 290^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 291 292The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 293from Intel that was not properly allocated. Since version 5.2, the controller 294has used a properly allocated identifier. Deprecate the ``use-intel-id`` 295machine compatibility parameter. 296 297``-device cxl-type3,memdev=xxxx`` (since 8.0) 298^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 299 300The ``cxl-type3`` device initially only used a single memory backend. With 301the addition of volatile memory support, it is now necessary to distinguish 302between persistent and volatile memory backends. As such, memdev is deprecated 303in favor of persistent-memdev. 304 305``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 306^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 307 308The 9p ``proxy`` filesystem backend driver has been deprecated and will be 309removed (along with its proxy helper daemon) in a future version of QEMU. Please 310use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 311backend, or alternatively consider deploying virtiofsd instead. 312 313The 9p ``proxy`` backend was originally developed as an alternative to the 9p 314``local`` backend. The idea was to enhance security by dispatching actual low 315level filesystem operations from 9p server (QEMU process) over to a separate 316process (the virtfs-proxy-helper binary). However this alternative never gained 317momentum. The proxy backend is much slower than the local backend, hasn't seen 318any development in years, and showed to be less secure, especially due to the 319fact that its helper daemon must be run as root, whereas with the local backend 320QEMU is typically run as unprivileged user and allows to tighten behaviour by 321mapping permissions et al by using its 'mapped' security model option. 322 323Nowadays it would make sense to reimplement the ``proxy`` backend by using 324QEMU's ``vhost`` feature, which would eliminate the high latency costs under 325which the 9p ``proxy`` backend currently suffers. However as of to date nobody 326has indicated plans for such kind of reimplementation unfortunately. 327 328RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 329^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 330 331The 'any' CPU type was introduced back in 2018 and has been around since the 332initial RISC-V QEMU port. Its usage has always been unclear: users don't know 333what to expect from a CPU called 'any', and in fact the CPU does not do anything 334special that isn't already done by the default CPUs rv32/rv64. 335 336After the introduction of the 'max' CPU type, RISC-V now has a good coverage 337of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 338CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 339CPU type starting in 8.2. 340 341RISC-V CPU properties which start with capital 'Z' (since 8.2) 342^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 343 344All RISC-V CPU properties which start with capital 'Z' are being deprecated 345starting in 8.2. The reason is that they were wrongly added with capital 'Z' 346in the past. CPU properties were later added with lower-case names, which 347is the format we want to use from now on. 348 349Users which try to use these deprecated properties will receive a warning 350recommending to switch to their stable counterparts: 351 352- "Zifencei" should be replaced with "zifencei" 353- "Zicsr" should be replaced with "zicsr" 354- "Zihintntl" should be replaced with "zihintntl" 355- "Zihintpause" should be replaced with "zihintpause" 356- "Zawrs" should be replaced with "zawrs" 357- "Zfa" should be replaced with "zfa" 358- "Zfh" should be replaced with "zfh" 359- "Zfhmin" should be replaced with "zfhmin" 360- "Zve32f" should be replaced with "zve32f" 361- "Zve64f" should be replaced with "zve64f" 362- "Zve64d" should be replaced with "zve64d" 363 364``-device pvrdma`` and the rdma subsystem (since 8.2) 365^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 366 367The pvrdma device and the whole rdma subsystem are in a bad shape and 368without active maintenance. The QEMU project intends to remove this 369device and subsystem from the code base in a future release without 370replacement unless somebody steps up and improves the situation. 371 372 373Block device options 374'''''''''''''''''''' 375 376``"backing": ""`` (since 2.12) 377^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 378 379In order to prevent QEMU from automatically opening an image's backing 380chain, use ``"backing": null`` instead. 381 382``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 383^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 384 385Options for ``rbd`` should be specified according to its runtime options, 386like other block drivers. Legacy parsing of keyvalue pair encoded 387filenames is useful to open images with the old format for backing files; 388These image files should be updated to use the current format. 389 390Example of legacy encoding:: 391 392 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 393 394The above, converted to the current supported format:: 395 396 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 397 398``iscsi,password=xxx`` (since 8.0) 399^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 400 401Specifying the iSCSI password in plain text on the command line using the 402``password`` option is insecure. The ``password-secret`` option should be 403used instead, to refer to a ``--object secret...`` instance that provides 404a password via a file, or encrypted. 405 406Character device options 407'''''''''''''''''''''''' 408 409Backend ``memory`` (since 9.0) 410^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 411 412``memory`` is a deprecated synonym for ``ringbuf``. 413 414CPU device properties 415''''''''''''''''''''' 416 417``pmu-num=n`` on RISC-V CPUs (since 8.2) 418^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 419 420In order to support more flexible counter configurations this has been replaced 421by a ``pmu-mask`` property. If set of counters is continuous then the mask can 422be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 423must be left clear. 424 425 426Backwards compatibility 427----------------------- 428 429Runnability guarantee of CPU models (since 4.1) 430''''''''''''''''''''''''''''''''''''''''''''''' 431 432Previous versions of QEMU never changed existing CPU models in 433ways that introduced additional host software or hardware 434requirements to the VM. This allowed management software to 435safely change the machine type of an existing VM without 436introducing new requirements ("runnability guarantee"). This 437prevented CPU models from being updated to include CPU 438vulnerability mitigations, leaving guests vulnerable in the 439default configuration. 440 441The CPU model runnability guarantee won't apply anymore to 442existing CPU models. Management software that needs runnability 443guarantees must resolve the CPU model aliases using the 444``alias-of`` field returned by the ``query-cpu-definitions`` QMP 445command. 446 447While those guarantees are kept, the return value of 448``query-cpu-definitions`` will have existing CPU model aliases 449point to a version that doesn't break runnability guarantees 450(specifically, version 1 of those CPU models). In future QEMU 451versions, aliases will point to newer CPU model versions 452depending on the machine type, so management software must 453resolve CPU model aliases before starting a virtual machine. 454 455QEMU guest agent 456---------------- 457 458``--blacklist`` command line option (since 7.2) 459''''''''''''''''''''''''''''''''''''''''''''''' 460 461``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 462wording for what this option does). The short form ``-b`` still stays 463the same and thus is the preferred way for scripts that should run with 464both, older and future versions of QEMU. 465 466``blacklist`` config file option (since 7.2) 467'''''''''''''''''''''''''''''''''''''''''''' 468 469The ``blacklist`` config file option has been renamed to ``block-rpcs`` 470(to be in sync with the renaming of the corresponding command line 471option). 472 473Migration 474--------- 475 476``skipped`` MigrationStats field (since 8.1) 477'''''''''''''''''''''''''''''''''''''''''''' 478 479``skipped`` field in Migration stats has been deprecated. It hasn't 480been used for more than 10 years. 481 482``inc`` migrate command option (since 8.2) 483'''''''''''''''''''''''''''''''''''''''''' 484 485Use blockdev-mirror with NBD instead. 486 487As an intermediate step the ``inc`` functionality can be achieved by 488setting the ``block-incremental`` migration parameter to ``true``. 489But this parameter is also deprecated. 490 491``blk`` migrate command option (since 8.2) 492'''''''''''''''''''''''''''''''''''''''''' 493 494Use blockdev-mirror with NBD instead. 495 496As an intermediate step the ``blk`` functionality can be achieved by 497setting the ``block`` migration capability to ``true``. But this 498capability is also deprecated. 499 500block migration (since 8.2) 501''''''''''''''''''''''''''' 502 503Block migration is too inflexible. It needs to migrate all block 504devices or none. 505 506Please see "QMP invocation for live storage migration with 507``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst 508for a detailed explanation. 509 510old compression method (since 8.2) 511'''''''''''''''''''''''''''''''''' 512 513Compression method fails too much. Too many races. We are going to 514remove it if nobody fixes it. For starters, migration-test 515compression tests are disabled because they fail randomly. If you need 516compression, use multifd compression methods. 517