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 66``-no-hpet`` (since 8.0) 67'''''''''''''''''''''''' 68 69The HPET setting has been turned into a machine property. 70Use ``-machine hpet=off`` instead. 71 72``-no-acpi`` (since 8.0) 73'''''''''''''''''''''''' 74 75The ``-no-acpi`` setting has been turned into a machine property. 76Use ``-machine acpi=off`` instead. 77 78``-async-teardown`` (since 8.1) 79''''''''''''''''''''''''''''''' 80 81Use ``-run-with async-teardown=on`` instead. 82 83``-chroot`` (since 8.1) 84''''''''''''''''''''''' 85 86Use ``-run-with chroot=dir`` instead. 87 88``-singlestep`` (since 8.1) 89''''''''''''''''''''''''''' 90 91The ``-singlestep`` option has been turned into an accelerator property, 92and given a name that better reflects what it actually does. 93Use ``-accel tcg,one-insn-per-tb=on`` instead. 94 95User-mode emulator command line arguments 96----------------------------------------- 97 98``-singlestep`` (since 8.1) 99''''''''''''''''''''''''''' 100 101The ``-singlestep`` option has been given a name that better reflects 102what it actually does. For both linux-user and bsd-user, use the 103new ``-one-insn-per-tb`` option instead. 104 105QEMU Machine Protocol (QMP) commands 106------------------------------------ 107 108``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 109''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 110 111Use argument ``id`` instead. 112 113``eject`` argument ``device`` (since 2.8) 114''''''''''''''''''''''''''''''''''''''''' 115 116Use argument ``id`` instead. 117 118``blockdev-change-medium`` argument ``device`` (since 2.8) 119'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 120 121Use argument ``id`` instead. 122 123``block_set_io_throttle`` argument ``device`` (since 2.8) 124''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 125 126Use argument ``id`` instead. 127 128``blockdev-add`` empty string argument ``backing`` (since 2.10) 129''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 130 131Use argument value ``null`` instead. 132 133``block-commit`` arguments ``base`` and ``top`` (since 3.1) 134''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 135 136Use arguments ``base-node`` and ``top-node`` instead. 137 138``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 139'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 140 141Use the more generic commands ``block-export-add`` and ``block-export-del`` 142instead. As part of this deprecation, where ``nbd-server-add`` used a 143single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 144 145``query-qmp-schema`` return value member ``values`` (since 6.2) 146''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 147 148Member ``values`` in return value elements with meta-type ``enum`` is 149deprecated. Use ``members`` instead. 150 151``drive-backup`` (since 6.2) 152'''''''''''''''''''''''''''' 153 154Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 155This change primarily separates the creation/opening process of the backup 156target with explicit, separate steps. ``blockdev-backup`` uses mostly the 157same arguments as ``drive-backup``, except the ``format`` and ``mode`` 158options are removed in favor of using explicit ``blockdev-create`` and 159``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 160details. 161 162Incorrectly typed ``device_add`` arguments (since 6.2) 163'''''''''''''''''''''''''''''''''''''''''''''''''''''' 164 165Due to shortcomings in the internal implementation of ``device_add``, QEMU 166incorrectly accepts certain invalid arguments: Any object or list arguments are 167silently ignored. Other argument types are not checked, but an implicit 168conversion happens, so that e.g. string values can be assigned to integer 169device properties or vice versa. 170 171This is a bug in QEMU that will be fixed in the future so that previously 172accepted incorrect commands will return an error. Users should make sure that 173all arguments passed to ``device_add`` are consistent with the documented 174property types. 175 176``StatusInfo`` member ``singlestep`` (since 8.1) 177'''''''''''''''''''''''''''''''''''''''''''''''' 178 179The ``singlestep`` member of the ``StatusInfo`` returned from the 180``query-status`` command is deprecated. This member has a confusing 181name and it never did what the documentation claimed or what its name 182suggests. We do not believe that anybody is actually using the 183information provided in this member. 184 185The information it reports is whether the TCG JIT is in "one 186instruction per translated block" mode (which can be set on the 187command line or via the HMP, but not via QMP). The information remains 188available via the HMP 'info jit' command. 189 190QEMU Machine Protocol (QMP) events 191---------------------------------- 192 193``MEM_UNPLUG_ERROR`` (since 6.2) 194'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 195 196Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead. 197 198``vcpu`` trace events (since 8.1) 199''''''''''''''''''''''''''''''''' 200 201The ability to instrument QEMU helper functions with vCPU-aware trace 202points was removed in 7.0. However QMP still exposed the vcpu 203parameter. This argument has now been deprecated and the remaining 204remaining trace points that used it are selected just by name. 205 206Human Monitor Protocol (HMP) commands 207------------------------------------- 208 209``singlestep`` (since 8.1) 210'''''''''''''''''''''''''' 211 212The ``singlestep`` command has been replaced by the ``one-insn-per-tb`` 213command, which has the same behaviour but a less misleading name. 214 215Host Architectures 216------------------ 217 218BE MIPS (since 7.2) 219''''''''''''''''''' 220 221As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 222MIPS moved out of support making it hard to maintain our 223cross-compilation CI tests of the architecture. As we no longer have 224CI coverage support may bitrot away before the deprecation process 225completes. The little endian variants of MIPS (both 32 and 64 bit) are 226still a supported host architecture. 227 228System emulation on 32-bit x86 hosts (since 8.0) 229'''''''''''''''''''''''''''''''''''''''''''''''' 230 231Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 232OS distributions given the widespread availability of 64-bit x86 hardware. 233The QEMU project no longer considers 32-bit x86 support for system emulation to 234be an effective use of its limited resources, and thus intends to discontinue 235it. Since all recent x86 hardware from the past >10 years is capable of the 23664-bit x86 extensions, a corresponding 64-bit OS should be used instead. 237 238 239System emulator machines 240------------------------ 241 242Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 243'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 244 245The ``dtb-kaslr-seed`` property on the ``virt`` board has been 246deprecated; use the new name ``dtb-randomness`` instead. The new name 247better reflects the way this property affects all random data within 248the device tree blob, not just the ``kaslr-seed`` node. 249 250``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2) 251''''''''''''''''''''''''''''''''''''''''''''''''''''' 252 253These old machine types are quite neglected nowadays and thus might have 254various pitfalls with regards to live migration. Use a newer machine type 255instead. 256 257 258Backend options 259--------------- 260 261Using non-persistent backing file with pmem=on (since 6.1) 262'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 263 264This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 265device. However enabling ``memory-backend-file.pmem`` option, when backing file 266is (a) not DAX capable or (b) not on a filesystem that support direct mapping 267of persistent memory, is not safe and may lead to data loss or corruption in case 268of host crash. 269Options are: 270 271 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 272 (without persistence guaranties) with backing file on non DAX storage 273 - move backing file to NVDIMM storage and keep ``pmem=on`` 274 (to have NVDIMM with persistence guaranties). 275 276Device options 277-------------- 278 279Emulated device options 280''''''''''''''''''''''' 281 282``-device virtio-blk,scsi=on|off`` (since 5.0) 283^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 284 285The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 286and later do not support it because the virtio-scsi device was introduced for 287full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 288 289Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 290alias. 291 292``-device nvme-ns,eui64-default=on|off`` (since 7.1) 293^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 294 295In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 296identifier that is not globally unique. If an EUI-64 identifier is required, the 297user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 298 299``-device nvme,use-intel-id=on|off`` (since 7.1) 300^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 301 302The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 303from Intel that was not properly allocated. Since version 5.2, the controller 304has used a properly allocated identifier. Deprecate the ``use-intel-id`` 305machine compatibility parameter. 306 307``-device cxl-type3,memdev=xxxx`` (since 8.0) 308^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 309 310The ``cxl-type3`` device initially only used a single memory backend. With 311the addition of volatile memory support, it is now necessary to distinguish 312between persistent and volatile memory backends. As such, memdev is deprecated 313in favor of persistent-memdev. 314 315``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 316^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 317 318The 9p ``proxy`` filesystem backend driver has been deprecated and will be 319removed (along with its proxy helper daemon) in a future version of QEMU. Please 320use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 321backend, or alternatively consider deploying virtiofsd instead. 322 323The 9p ``proxy`` backend was originally developed as an alternative to the 9p 324``local`` backend. The idea was to enhance security by dispatching actual low 325level filesystem operations from 9p server (QEMU process) over to a separate 326process (the virtfs-proxy-helper binary). However this alternative never gained 327momentum. The proxy backend is much slower than the local backend, hasn't seen 328any development in years, and showed to be less secure, especially due to the 329fact that its helper daemon must be run as root, whereas with the local backend 330QEMU is typically run as unprivileged user and allows to tighten behaviour by 331mapping permissions et al by using its 'mapped' security model option. 332 333Nowadays it would make sense to reimplement the ``proxy`` backend by using 334QEMU's ``vhost`` feature, which would eliminate the high latency costs under 335which the 9p ``proxy`` backend currently suffers. However as of to date nobody 336has indicated plans for such kind of reimplementation unfortunately. 337 338RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 339^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 340 341The 'any' CPU type was introduced back in 2018 and has been around since the 342initial RISC-V QEMU port. Its usage has always been unclear: users don't know 343what to expect from a CPU called 'any', and in fact the CPU does not do anything 344special that isn't already done by the default CPUs rv32/rv64. 345 346After the introduction of the 'max' CPU type, RISC-V now has a good coverage 347of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 348CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 349CPU type starting in 8.2. 350 351RISC-V CPU properties which start with capital 'Z' (since 8.2) 352^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 353 354All RISC-V CPU properties which start with capital 'Z' are being deprecated 355starting in 8.2. The reason is that they were wrongly added with capital 'Z' 356in the past. CPU properties were later added with lower-case names, which 357is the format we want to use from now on. 358 359Users which try to use these deprecated properties will receive a warning 360recommending to switch to their stable counterparts: 361 362- "Zifencei" should be replaced with "zifencei" 363- "Zicsr" should be replaced with "zicsr" 364- "Zihintntl" should be replaced with "zihintntl" 365- "Zihintpause" should be replaced with "zihintpause" 366- "Zawrs" should be replaced with "zawrs" 367- "Zfa" should be replaced with "zfa" 368- "Zfh" should be replaced with "zfh" 369- "Zfhmin" should be replaced with "zfhmin" 370- "Zve32f" should be replaced with "zve32f" 371- "Zve64f" should be replaced with "zve64f" 372- "Zve64d" should be replaced with "zve64d" 373 374``-device pvrdma`` and the rdma subsystem (since 8.2) 375^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 376 377The pvrdma device and the whole rdma subsystem are in a bad shape and 378without active maintenance. The QEMU project intends to remove this 379device and subsystem from the code base in a future release without 380replacement unless somebody steps up and improves the situation. 381 382 383Block device options 384'''''''''''''''''''' 385 386``"backing": ""`` (since 2.12) 387^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 388 389In order to prevent QEMU from automatically opening an image's backing 390chain, use ``"backing": null`` instead. 391 392``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 393^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 394 395Options for ``rbd`` should be specified according to its runtime options, 396like other block drivers. Legacy parsing of keyvalue pair encoded 397filenames is useful to open images with the old format for backing files; 398These image files should be updated to use the current format. 399 400Example of legacy encoding:: 401 402 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 403 404The above, converted to the current supported format:: 405 406 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 407 408``iscsi,password=xxx`` (since 8.0) 409^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 410 411Specifying the iSCSI password in plain text on the command line using the 412``password`` option is insecure. The ``password-secret`` option should be 413used instead, to refer to a ``--object secret...`` instance that provides 414a password via a file, or encrypted. 415 416CPU device properties 417''''''''''''''''''''' 418 419``pmu-num=n`` on RISC-V CPUs (since 8.2) 420^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 421 422In order to support more flexible counter configurations this has been replaced 423by a ``pmu-mask`` property. If set of counters is continuous then the mask can 424be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 425must be left clear. 426 427 428Backwards compatibility 429----------------------- 430 431Runnability guarantee of CPU models (since 4.1) 432''''''''''''''''''''''''''''''''''''''''''''''' 433 434Previous versions of QEMU never changed existing CPU models in 435ways that introduced additional host software or hardware 436requirements to the VM. This allowed management software to 437safely change the machine type of an existing VM without 438introducing new requirements ("runnability guarantee"). This 439prevented CPU models from being updated to include CPU 440vulnerability mitigations, leaving guests vulnerable in the 441default configuration. 442 443The CPU model runnability guarantee won't apply anymore to 444existing CPU models. Management software that needs runnability 445guarantees must resolve the CPU model aliases using the 446``alias-of`` field returned by the ``query-cpu-definitions`` QMP 447command. 448 449While those guarantees are kept, the return value of 450``query-cpu-definitions`` will have existing CPU model aliases 451point to a version that doesn't break runnability guarantees 452(specifically, version 1 of those CPU models). In future QEMU 453versions, aliases will point to newer CPU model versions 454depending on the machine type, so management software must 455resolve CPU model aliases before starting a virtual machine. 456 457QEMU guest agent 458---------------- 459 460``--blacklist`` command line option (since 7.2) 461''''''''''''''''''''''''''''''''''''''''''''''' 462 463``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 464wording for what this option does). The short form ``-b`` still stays 465the same and thus is the preferred way for scripts that should run with 466both, older and future versions of QEMU. 467 468``blacklist`` config file option (since 7.2) 469'''''''''''''''''''''''''''''''''''''''''''' 470 471The ``blacklist`` config file option has been renamed to ``block-rpcs`` 472(to be in sync with the renaming of the corresponding command line 473option). 474 475Migration 476--------- 477 478``skipped`` MigrationStats field (since 8.1) 479'''''''''''''''''''''''''''''''''''''''''''' 480 481``skipped`` field in Migration stats has been deprecated. It hasn't 482been used for more than 10 years. 483 484``inc`` migrate command option (since 8.2) 485'''''''''''''''''''''''''''''''''''''''''' 486 487Use blockdev-mirror with NBD instead. 488 489As an intermediate step the ``inc`` functionality can be achieved by 490setting the ``block-incremental`` migration parameter to ``true``. 491But this parameter is also deprecated. 492 493``blk`` migrate command option (since 8.2) 494'''''''''''''''''''''''''''''''''''''''''' 495 496Use blockdev-mirror with NBD instead. 497 498As an intermediate step the ``blk`` functionality can be achieved by 499setting the ``block`` migration capability to ``true``. But this 500capability is also deprecated. 501 502block migration (since 8.2) 503''''''''''''''''''''''''''' 504 505Block migration is too inflexible. It needs to migrate all block 506devices or none. 507 508Please see "QMP invocation for live storage migration with 509``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst 510for a detailed explanation. 511 512old compression method (since 8.2) 513'''''''''''''''''''''''''''''''''' 514 515Compression method fails too much. Too many races. We are going to 516remove it if nobody fixes it. For starters, migration-test 517compression tests are disabled becase they fail randomly. If you need 518compression, use multifd compression methods. 519