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