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 39``-smp`` ("parameter=0" SMP configurations) (since 6.2) 40''''''''''''''''''''''''''''''''''''''''''''''''''''''' 41 42Specified CPU topology parameters must be greater than zero. 43 44In the SMP configuration, users should either provide a CPU topology 45parameter with a reasonable value (greater than zero) or just omit it 46and QEMU will compute the missing value. 47 48However, historically it was implicitly allowed for users to provide 49a parameter with zero value, which is meaningless and could also possibly 50cause unexpected results in the -smp parsing. So support for this kind of 51configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will 52be removed in the near future, users have to ensure that all the topology 53members described with -smp are greater than zero. 54 55Plugin argument passing through ``arg=<string>`` (since 6.1) 56'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 57 58Passing TCG plugins arguments through ``arg=`` is redundant is makes the 59command-line less readable, especially when the argument itself consist of a 60name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``. 61Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated 62as short-form boolean values, and passed to plugins as ``arg_name=on``. 63However, short-form booleans are deprecated and full explicit ``arg_name=on`` 64form is preferred. 65 66QEMU Machine Protocol (QMP) commands 67------------------------------------ 68 69``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 70''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 71 72Use argument ``id`` instead. 73 74``eject`` argument ``device`` (since 2.8) 75''''''''''''''''''''''''''''''''''''''''' 76 77Use argument ``id`` instead. 78 79``blockdev-change-medium`` argument ``device`` (since 2.8) 80'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 81 82Use argument ``id`` instead. 83 84``block_set_io_throttle`` argument ``device`` (since 2.8) 85''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 86 87Use argument ``id`` instead. 88 89``blockdev-add`` empty string argument ``backing`` (since 2.10) 90''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 91 92Use argument value ``null`` instead. 93 94``block-commit`` arguments ``base`` and ``top`` (since 3.1) 95''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 96 97Use arguments ``base-node`` and ``top-node`` instead. 98 99``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 100'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 101 102Use the more generic commands ``block-export-add`` and ``block-export-del`` 103instead. As part of this deprecation, where ``nbd-server-add`` used a 104single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 105 106``query-qmp-schema`` return value member ``values`` (since 6.2) 107''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 108 109Member ``values`` in return value elements with meta-type ``enum`` is 110deprecated. Use ``members`` instead. 111 112``drive-backup`` (since 6.2) 113'''''''''''''''''''''''''''' 114 115Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 116This change primarily separates the creation/opening process of the backup 117target with explicit, separate steps. ``blockdev-backup`` uses mostly the 118same arguments as ``drive-backup``, except the ``format`` and ``mode`` 119options are removed in favor of using explicit ``blockdev-create`` and 120``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 121details. 122 123Incorrectly typed ``device_add`` arguments (since 6.2) 124'''''''''''''''''''''''''''''''''''''''''''''''''''''' 125 126Due to shortcomings in the internal implementation of ``device_add``, QEMU 127incorrectly accepts certain invalid arguments: Any object or list arguments are 128silently ignored. Other argument types are not checked, but an implicit 129conversion happens, so that e.g. string values can be assigned to integer 130device properties or vice versa. 131 132This is a bug in QEMU that will be fixed in the future so that previously 133accepted incorrect commands will return an error. Users should make sure that 134all arguments passed to ``device_add`` are consistent with the documented 135property types. 136 137QEMU Machine Protocol (QMP) events 138---------------------------------- 139 140``MEM_UNPLUG_ERROR`` (since 6.2) 141'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 142 143Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead. 144 145``vcpu`` trace events (since 8.1) 146''''''''''''''''''''''''''''''''' 147 148The ability to instrument QEMU helper functions with vCPU-aware trace 149points was removed in 7.0. However QMP still exposed the vcpu 150parameter. This argument has now been deprecated and the remaining 151remaining trace points that used it are selected just by name. 152 153Host Architectures 154------------------ 155 156BE MIPS (since 7.2) 157''''''''''''''''''' 158 159As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 160MIPS moved out of support making it hard to maintain our 161cross-compilation CI tests of the architecture. As we no longer have 162CI coverage support may bitrot away before the deprecation process 163completes. The little endian variants of MIPS (both 32 and 64 bit) are 164still a supported host architecture. 165 166System emulation on 32-bit x86 hosts (since 8.0) 167'''''''''''''''''''''''''''''''''''''''''''''''' 168 169Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 170OS distributions given the widespread availability of 64-bit x86 hardware. 171The QEMU project no longer considers 32-bit x86 support for system emulation to 172be an effective use of its limited resources, and thus intends to discontinue 173it. Since all recent x86 hardware from the past >10 years is capable of the 17464-bit x86 extensions, a corresponding 64-bit OS should be used instead. 175 176 177System emulator CPUs 178-------------------- 179 180Nios II CPU (since 8.2) 181''''''''''''''''''''''' 182 183The Nios II architecture is orphan. The ``nios2`` guest CPU support is 184deprecated and will be removed in a future version of QEMU. 185 186``power5+`` and ``power7+`` CPU names (since 9.0) 187''''''''''''''''''''''''''''''''''''''''''''''''' 188 189The character "+" in device (and thus also CPU) names is not allowed 190in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``, 191``power7+`` and ``power7+_v2.1`` are currently still supported via 192an alias, but for consistency these will get removed in a future 193release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead. 194 195CRIS CPU architecture (since 9.0) 196''''''''''''''''''''''''''''''''' 197 198The CRIS architecture was pulled from Linux in 4.17 and the compiler 199is no longer packaged in any distro making it harder to run the 200``check-tcg`` tests. Unless we can improve the testing situation there 201is a chance the code will bitrot without anyone noticing. 202 203System emulator machines 204------------------------ 205 206Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 207'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 208 209The ``dtb-kaslr-seed`` property on the ``virt`` board has been 210deprecated; use the new name ``dtb-randomness`` instead. The new name 211better reflects the way this property affects all random data within 212the device tree blob, not just the ``kaslr-seed`` node. 213 214``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2) 215''''''''''''''''''''''''''''''''''''''''''''''''''''' 216 217These old machine types are quite neglected nowadays and thus might have 218various pitfalls with regards to live migration. Use a newer machine type 219instead. 220 221Nios II ``10m50-ghrd`` and ``nios2-generic-nommu`` machines (since 8.2) 222''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 223 224The Nios II architecture is orphan. 225 226``shix`` (since 9.0) 227'''''''''''''''''''' 228 229The machine is no longer in existence and has been long unmaintained 230in QEMU. This also holds for the TC51828 16MiB flash that it uses. 231 232``pseries-2.1`` up to ``pseries-2.11`` (since 9.0) 233'''''''''''''''''''''''''''''''''''''''''''''''''' 234 235Older pseries machines before version 2.12 have undergone many changes 236to correct issues, mostly regarding migration compatibility. These are 237no longer maintained and removing them will make the code easier to 238read and maintain. Use versions 2.12 and above as a replacement. 239 240Backend options 241--------------- 242 243Using non-persistent backing file with pmem=on (since 6.1) 244'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 245 246This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 247device. However enabling ``memory-backend-file.pmem`` option, when backing file 248is (a) not DAX capable or (b) not on a filesystem that support direct mapping 249of persistent memory, is not safe and may lead to data loss or corruption in case 250of host crash. 251Options are: 252 253 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 254 (without persistence guaranties) with backing file on non DAX storage 255 - move backing file to NVDIMM storage and keep ``pmem=on`` 256 (to have NVDIMM with persistence guaranties). 257 258Device options 259-------------- 260 261Emulated device options 262''''''''''''''''''''''' 263 264``-device virtio-blk,scsi=on|off`` (since 5.0) 265^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 266 267The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 268and later do not support it because the virtio-scsi device was introduced for 269full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 270 271Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 272alias. 273 274``-device nvme-ns,eui64-default=on|off`` (since 7.1) 275^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 276 277In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 278identifier that is not globally unique. If an EUI-64 identifier is required, the 279user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 280 281``-device nvme,use-intel-id=on|off`` (since 7.1) 282^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 283 284The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 285from Intel that was not properly allocated. Since version 5.2, the controller 286has used a properly allocated identifier. Deprecate the ``use-intel-id`` 287machine compatibility parameter. 288 289``-device cxl-type3,memdev=xxxx`` (since 8.0) 290^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 291 292The ``cxl-type3`` device initially only used a single memory backend. With 293the addition of volatile memory support, it is now necessary to distinguish 294between persistent and volatile memory backends. As such, memdev is deprecated 295in favor of persistent-memdev. 296 297``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 298^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 299 300The 9p ``proxy`` filesystem backend driver has been deprecated and will be 301removed (along with its proxy helper daemon) in a future version of QEMU. Please 302use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 303backend, or alternatively consider deploying virtiofsd instead. 304 305The 9p ``proxy`` backend was originally developed as an alternative to the 9p 306``local`` backend. The idea was to enhance security by dispatching actual low 307level filesystem operations from 9p server (QEMU process) over to a separate 308process (the virtfs-proxy-helper binary). However this alternative never gained 309momentum. The proxy backend is much slower than the local backend, hasn't seen 310any development in years, and showed to be less secure, especially due to the 311fact that its helper daemon must be run as root, whereas with the local backend 312QEMU is typically run as unprivileged user and allows to tighten behaviour by 313mapping permissions et al by using its 'mapped' security model option. 314 315Nowadays it would make sense to reimplement the ``proxy`` backend by using 316QEMU's ``vhost`` feature, which would eliminate the high latency costs under 317which the 9p ``proxy`` backend currently suffers. However as of to date nobody 318has indicated plans for such kind of reimplementation unfortunately. 319 320RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 321^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 322 323The 'any' CPU type was introduced back in 2018 and has been around since the 324initial RISC-V QEMU port. Its usage has always been unclear: users don't know 325what to expect from a CPU called 'any', and in fact the CPU does not do anything 326special that isn't already done by the default CPUs rv32/rv64. 327 328After the introduction of the 'max' CPU type, RISC-V now has a good coverage 329of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 330CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 331CPU type starting in 8.2. 332 333RISC-V CPU properties which start with capital 'Z' (since 8.2) 334^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 335 336All RISC-V CPU properties which start with capital 'Z' are being deprecated 337starting in 8.2. The reason is that they were wrongly added with capital 'Z' 338in the past. CPU properties were later added with lower-case names, which 339is the format we want to use from now on. 340 341Users which try to use these deprecated properties will receive a warning 342recommending to switch to their stable counterparts: 343 344- "Zifencei" should be replaced with "zifencei" 345- "Zicsr" should be replaced with "zicsr" 346- "Zihintntl" should be replaced with "zihintntl" 347- "Zihintpause" should be replaced with "zihintpause" 348- "Zawrs" should be replaced with "zawrs" 349- "Zfa" should be replaced with "zfa" 350- "Zfh" should be replaced with "zfh" 351- "Zfhmin" should be replaced with "zfhmin" 352- "Zve32f" should be replaced with "zve32f" 353- "Zve64f" should be replaced with "zve64f" 354- "Zve64d" should be replaced with "zve64d" 355 356``-device pvrdma`` and the rdma subsystem (since 8.2) 357^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 358 359The pvrdma device and the whole rdma subsystem are in a bad shape and 360without active maintenance. The QEMU project intends to remove this 361device and subsystem from the code base in a future release without 362replacement unless somebody steps up and improves the situation. 363 364 365Block device options 366'''''''''''''''''''' 367 368``"backing": ""`` (since 2.12) 369^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 370 371In order to prevent QEMU from automatically opening an image's backing 372chain, use ``"backing": null`` instead. 373 374``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 375^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 376 377Options for ``rbd`` should be specified according to its runtime options, 378like other block drivers. Legacy parsing of keyvalue pair encoded 379filenames is useful to open images with the old format for backing files; 380These image files should be updated to use the current format. 381 382Example of legacy encoding:: 383 384 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 385 386The above, converted to the current supported format:: 387 388 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 389 390``iscsi,password=xxx`` (since 8.0) 391^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 392 393Specifying the iSCSI password in plain text on the command line using the 394``password`` option is insecure. The ``password-secret`` option should be 395used instead, to refer to a ``--object secret...`` instance that provides 396a password via a file, or encrypted. 397 398Character device options 399'''''''''''''''''''''''' 400 401Backend ``memory`` (since 9.0) 402^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 403 404``memory`` is a deprecated synonym for ``ringbuf``. 405 406CPU device properties 407''''''''''''''''''''' 408 409``pmu-num=n`` on RISC-V CPUs (since 8.2) 410^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 411 412In order to support more flexible counter configurations this has been replaced 413by a ``pmu-mask`` property. If set of counters is continuous then the mask can 414be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 415must be left clear. 416 417 418Backwards compatibility 419----------------------- 420 421Runnability guarantee of CPU models (since 4.1) 422''''''''''''''''''''''''''''''''''''''''''''''' 423 424Previous versions of QEMU never changed existing CPU models in 425ways that introduced additional host software or hardware 426requirements to the VM. This allowed management software to 427safely change the machine type of an existing VM without 428introducing new requirements ("runnability guarantee"). This 429prevented CPU models from being updated to include CPU 430vulnerability mitigations, leaving guests vulnerable in the 431default configuration. 432 433The CPU model runnability guarantee won't apply anymore to 434existing CPU models. Management software that needs runnability 435guarantees must resolve the CPU model aliases using the 436``alias-of`` field returned by the ``query-cpu-definitions`` QMP 437command. 438 439While those guarantees are kept, the return value of 440``query-cpu-definitions`` will have existing CPU model aliases 441point to a version that doesn't break runnability guarantees 442(specifically, version 1 of those CPU models). In future QEMU 443versions, aliases will point to newer CPU model versions 444depending on the machine type, so management software must 445resolve CPU model aliases before starting a virtual machine. 446 447QEMU guest agent 448---------------- 449 450``--blacklist`` command line option (since 7.2) 451''''''''''''''''''''''''''''''''''''''''''''''' 452 453``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 454wording for what this option does). The short form ``-b`` still stays 455the same and thus is the preferred way for scripts that should run with 456both, older and future versions of QEMU. 457 458``blacklist`` config file option (since 7.2) 459'''''''''''''''''''''''''''''''''''''''''''' 460 461The ``blacklist`` config file option has been renamed to ``block-rpcs`` 462(to be in sync with the renaming of the corresponding command line 463option). 464 465Migration 466--------- 467 468``skipped`` MigrationStats field (since 8.1) 469'''''''''''''''''''''''''''''''''''''''''''' 470 471``skipped`` field in Migration stats has been deprecated. It hasn't 472been used for more than 10 years. 473 474``inc`` migrate command option (since 8.2) 475'''''''''''''''''''''''''''''''''''''''''' 476 477Use blockdev-mirror with NBD instead. 478 479As an intermediate step the ``inc`` functionality can be achieved by 480setting the ``block-incremental`` migration parameter to ``true``. 481But this parameter is also deprecated. 482 483``blk`` migrate command option (since 8.2) 484'''''''''''''''''''''''''''''''''''''''''' 485 486Use blockdev-mirror with NBD instead. 487 488As an intermediate step the ``blk`` functionality can be achieved by 489setting the ``block`` migration capability to ``true``. But this 490capability is also deprecated. 491 492block migration (since 8.2) 493''''''''''''''''''''''''''' 494 495Block migration is too inflexible. It needs to migrate all block 496devices or none. 497 498Please see "QMP invocation for live storage migration with 499``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst 500for a detailed explanation. 501 502old compression method (since 8.2) 503'''''''''''''''''''''''''''''''''' 504 505Compression method fails too much. Too many races. We are going to 506remove it if nobody fixes it. For starters, migration-test 507compression tests are disabled because they fail randomly. If you need 508compression, use multifd compression methods. 509