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``-singlestep`` (since 8.1) 67''''''''''''''''''''''''''' 68 69The ``-singlestep`` option has been turned into an accelerator property, 70and given a name that better reflects what it actually does. 71Use ``-accel tcg,one-insn-per-tb=on`` instead. 72 73User-mode emulator command line arguments 74----------------------------------------- 75 76``-singlestep`` (since 8.1) 77''''''''''''''''''''''''''' 78 79The ``-singlestep`` option has been given a name that better reflects 80what it actually does. For both linux-user and bsd-user, use the 81new ``-one-insn-per-tb`` option instead. 82 83QEMU Machine Protocol (QMP) commands 84------------------------------------ 85 86``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 87''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 88 89Use argument ``id`` instead. 90 91``eject`` argument ``device`` (since 2.8) 92''''''''''''''''''''''''''''''''''''''''' 93 94Use argument ``id`` instead. 95 96``blockdev-change-medium`` argument ``device`` (since 2.8) 97'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 98 99Use argument ``id`` instead. 100 101``block_set_io_throttle`` argument ``device`` (since 2.8) 102''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 103 104Use argument ``id`` instead. 105 106``blockdev-add`` empty string argument ``backing`` (since 2.10) 107''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 108 109Use argument value ``null`` instead. 110 111``block-commit`` arguments ``base`` and ``top`` (since 3.1) 112''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 113 114Use arguments ``base-node`` and ``top-node`` instead. 115 116``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 117'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 118 119Use the more generic commands ``block-export-add`` and ``block-export-del`` 120instead. As part of this deprecation, where ``nbd-server-add`` used a 121single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 122 123``query-qmp-schema`` return value member ``values`` (since 6.2) 124''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 125 126Member ``values`` in return value elements with meta-type ``enum`` is 127deprecated. Use ``members`` instead. 128 129``drive-backup`` (since 6.2) 130'''''''''''''''''''''''''''' 131 132Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 133This change primarily separates the creation/opening process of the backup 134target with explicit, separate steps. ``blockdev-backup`` uses mostly the 135same arguments as ``drive-backup``, except the ``format`` and ``mode`` 136options are removed in favor of using explicit ``blockdev-create`` and 137``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 138details. 139 140Incorrectly typed ``device_add`` arguments (since 6.2) 141'''''''''''''''''''''''''''''''''''''''''''''''''''''' 142 143Due to shortcomings in the internal implementation of ``device_add``, QEMU 144incorrectly accepts certain invalid arguments: Any object or list arguments are 145silently ignored. Other argument types are not checked, but an implicit 146conversion happens, so that e.g. string values can be assigned to integer 147device properties or vice versa. 148 149This is a bug in QEMU that will be fixed in the future so that previously 150accepted incorrect commands will return an error. Users should make sure that 151all arguments passed to ``device_add`` are consistent with the documented 152property types. 153 154QEMU Machine Protocol (QMP) events 155---------------------------------- 156 157``MEM_UNPLUG_ERROR`` (since 6.2) 158'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 159 160Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead. 161 162``vcpu`` trace events (since 8.1) 163''''''''''''''''''''''''''''''''' 164 165The ability to instrument QEMU helper functions with vCPU-aware trace 166points was removed in 7.0. However QMP still exposed the vcpu 167parameter. This argument has now been deprecated and the remaining 168remaining trace points that used it are selected just by name. 169 170Human Monitor Protocol (HMP) commands 171------------------------------------- 172 173``singlestep`` (since 8.1) 174'''''''''''''''''''''''''' 175 176The ``singlestep`` command has been replaced by the ``one-insn-per-tb`` 177command, which has the same behaviour but a less misleading name. 178 179Host Architectures 180------------------ 181 182BE MIPS (since 7.2) 183''''''''''''''''''' 184 185As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 186MIPS moved out of support making it hard to maintain our 187cross-compilation CI tests of the architecture. As we no longer have 188CI coverage support may bitrot away before the deprecation process 189completes. The little endian variants of MIPS (both 32 and 64 bit) are 190still a supported host architecture. 191 192System emulation on 32-bit x86 hosts (since 8.0) 193'''''''''''''''''''''''''''''''''''''''''''''''' 194 195Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 196OS distributions given the widespread availability of 64-bit x86 hardware. 197The QEMU project no longer considers 32-bit x86 support for system emulation to 198be an effective use of its limited resources, and thus intends to discontinue 199it. Since all recent x86 hardware from the past >10 years is capable of the 20064-bit x86 extensions, a corresponding 64-bit OS should be used instead. 201 202 203System emulator CPUs 204-------------------- 205 206Nios II CPU (since 8.2) 207''''''''''''''''''''''' 208 209The Nios II architecture is orphan. The ``nios2`` guest CPU support is 210deprecated and will be removed in a future version of QEMU. 211 212 213System emulator machines 214------------------------ 215 216Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 217'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 218 219The ``dtb-kaslr-seed`` property on the ``virt`` board has been 220deprecated; use the new name ``dtb-randomness`` instead. The new name 221better reflects the way this property affects all random data within 222the device tree blob, not just the ``kaslr-seed`` node. 223 224``pc-i440fx-2.0`` up to ``pc-i440fx-2.3`` (since 8.2) 225''''''''''''''''''''''''''''''''''''''''''''''''''''' 226 227These old machine types are quite neglected nowadays and thus might have 228various pitfalls with regards to live migration. Use a newer machine type 229instead. 230 231Nios II ``10m50-ghrd`` and ``nios2-generic-nommu`` machines (since 8.2) 232''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 233 234The Nios II architecture is orphan. 235 236 237Backend options 238--------------- 239 240Using non-persistent backing file with pmem=on (since 6.1) 241'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 242 243This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 244device. However enabling ``memory-backend-file.pmem`` option, when backing file 245is (a) not DAX capable or (b) not on a filesystem that support direct mapping 246of persistent memory, is not safe and may lead to data loss or corruption in case 247of host crash. 248Options are: 249 250 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 251 (without persistence guaranties) with backing file on non DAX storage 252 - move backing file to NVDIMM storage and keep ``pmem=on`` 253 (to have NVDIMM with persistence guaranties). 254 255Device options 256-------------- 257 258Emulated device options 259''''''''''''''''''''''' 260 261``-device virtio-blk,scsi=on|off`` (since 5.0) 262^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 263 264The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 265and later do not support it because the virtio-scsi device was introduced for 266full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 267 268Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 269alias. 270 271``-device nvme-ns,eui64-default=on|off`` (since 7.1) 272^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 273 274In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 275identifier that is not globally unique. If an EUI-64 identifier is required, the 276user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 277 278``-device nvme,use-intel-id=on|off`` (since 7.1) 279^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 280 281The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 282from Intel that was not properly allocated. Since version 5.2, the controller 283has used a properly allocated identifier. Deprecate the ``use-intel-id`` 284machine compatibility parameter. 285 286``-device cxl-type3,memdev=xxxx`` (since 8.0) 287^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 288 289The ``cxl-type3`` device initially only used a single memory backend. With 290the addition of volatile memory support, it is now necessary to distinguish 291between persistent and volatile memory backends. As such, memdev is deprecated 292in favor of persistent-memdev. 293 294``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 295^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 296 297The 9p ``proxy`` filesystem backend driver has been deprecated and will be 298removed (along with its proxy helper daemon) in a future version of QEMU. Please 299use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 300backend, or alternatively consider deploying virtiofsd instead. 301 302The 9p ``proxy`` backend was originally developed as an alternative to the 9p 303``local`` backend. The idea was to enhance security by dispatching actual low 304level filesystem operations from 9p server (QEMU process) over to a separate 305process (the virtfs-proxy-helper binary). However this alternative never gained 306momentum. The proxy backend is much slower than the local backend, hasn't seen 307any development in years, and showed to be less secure, especially due to the 308fact that its helper daemon must be run as root, whereas with the local backend 309QEMU is typically run as unprivileged user and allows to tighten behaviour by 310mapping permissions et al by using its 'mapped' security model option. 311 312Nowadays it would make sense to reimplement the ``proxy`` backend by using 313QEMU's ``vhost`` feature, which would eliminate the high latency costs under 314which the 9p ``proxy`` backend currently suffers. However as of to date nobody 315has indicated plans for such kind of reimplementation unfortunately. 316 317RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 318^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 319 320The 'any' CPU type was introduced back in 2018 and has been around since the 321initial RISC-V QEMU port. Its usage has always been unclear: users don't know 322what to expect from a CPU called 'any', and in fact the CPU does not do anything 323special that isn't already done by the default CPUs rv32/rv64. 324 325After the introduction of the 'max' CPU type, RISC-V now has a good coverage 326of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 327CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 328CPU type starting in 8.2. 329 330RISC-V CPU properties which start with capital 'Z' (since 8.2) 331^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 332 333All RISC-V CPU properties which start with capital 'Z' are being deprecated 334starting in 8.2. The reason is that they were wrongly added with capital 'Z' 335in the past. CPU properties were later added with lower-case names, which 336is the format we want to use from now on. 337 338Users which try to use these deprecated properties will receive a warning 339recommending to switch to their stable counterparts: 340 341- "Zifencei" should be replaced with "zifencei" 342- "Zicsr" should be replaced with "zicsr" 343- "Zihintntl" should be replaced with "zihintntl" 344- "Zihintpause" should be replaced with "zihintpause" 345- "Zawrs" should be replaced with "zawrs" 346- "Zfa" should be replaced with "zfa" 347- "Zfh" should be replaced with "zfh" 348- "Zfhmin" should be replaced with "zfhmin" 349- "Zve32f" should be replaced with "zve32f" 350- "Zve64f" should be replaced with "zve64f" 351- "Zve64d" should be replaced with "zve64d" 352 353``-device pvrdma`` and the rdma subsystem (since 8.2) 354^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 355 356The pvrdma device and the whole rdma subsystem are in a bad shape and 357without active maintenance. The QEMU project intends to remove this 358device and subsystem from the code base in a future release without 359replacement unless somebody steps up and improves the situation. 360 361 362Block device options 363'''''''''''''''''''' 364 365``"backing": ""`` (since 2.12) 366^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 367 368In order to prevent QEMU from automatically opening an image's backing 369chain, use ``"backing": null`` instead. 370 371``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 372^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 373 374Options for ``rbd`` should be specified according to its runtime options, 375like other block drivers. Legacy parsing of keyvalue pair encoded 376filenames is useful to open images with the old format for backing files; 377These image files should be updated to use the current format. 378 379Example of legacy encoding:: 380 381 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 382 383The above, converted to the current supported format:: 384 385 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 386 387``iscsi,password=xxx`` (since 8.0) 388^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 389 390Specifying the iSCSI password in plain text on the command line using the 391``password`` option is insecure. The ``password-secret`` option should be 392used instead, to refer to a ``--object secret...`` instance that provides 393a password via a file, or encrypted. 394 395CPU device properties 396''''''''''''''''''''' 397 398``pmu-num=n`` on RISC-V CPUs (since 8.2) 399^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 400 401In order to support more flexible counter configurations this has been replaced 402by a ``pmu-mask`` property. If set of counters is continuous then the mask can 403be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 404must be left clear. 405 406 407Backwards compatibility 408----------------------- 409 410Runnability guarantee of CPU models (since 4.1) 411''''''''''''''''''''''''''''''''''''''''''''''' 412 413Previous versions of QEMU never changed existing CPU models in 414ways that introduced additional host software or hardware 415requirements to the VM. This allowed management software to 416safely change the machine type of an existing VM without 417introducing new requirements ("runnability guarantee"). This 418prevented CPU models from being updated to include CPU 419vulnerability mitigations, leaving guests vulnerable in the 420default configuration. 421 422The CPU model runnability guarantee won't apply anymore to 423existing CPU models. Management software that needs runnability 424guarantees must resolve the CPU model aliases using the 425``alias-of`` field returned by the ``query-cpu-definitions`` QMP 426command. 427 428While those guarantees are kept, the return value of 429``query-cpu-definitions`` will have existing CPU model aliases 430point to a version that doesn't break runnability guarantees 431(specifically, version 1 of those CPU models). In future QEMU 432versions, aliases will point to newer CPU model versions 433depending on the machine type, so management software must 434resolve CPU model aliases before starting a virtual machine. 435 436QEMU guest agent 437---------------- 438 439``--blacklist`` command line option (since 7.2) 440''''''''''''''''''''''''''''''''''''''''''''''' 441 442``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 443wording for what this option does). The short form ``-b`` still stays 444the same and thus is the preferred way for scripts that should run with 445both, older and future versions of QEMU. 446 447``blacklist`` config file option (since 7.2) 448'''''''''''''''''''''''''''''''''''''''''''' 449 450The ``blacklist`` config file option has been renamed to ``block-rpcs`` 451(to be in sync with the renaming of the corresponding command line 452option). 453 454Migration 455--------- 456 457``skipped`` MigrationStats field (since 8.1) 458'''''''''''''''''''''''''''''''''''''''''''' 459 460``skipped`` field in Migration stats has been deprecated. It hasn't 461been used for more than 10 years. 462 463``inc`` migrate command option (since 8.2) 464'''''''''''''''''''''''''''''''''''''''''' 465 466Use blockdev-mirror with NBD instead. 467 468As an intermediate step the ``inc`` functionality can be achieved by 469setting the ``block-incremental`` migration parameter to ``true``. 470But this parameter is also deprecated. 471 472``blk`` migrate command option (since 8.2) 473'''''''''''''''''''''''''''''''''''''''''' 474 475Use blockdev-mirror with NBD instead. 476 477As an intermediate step the ``blk`` functionality can be achieved by 478setting the ``block`` migration capability to ``true``. But this 479capability is also deprecated. 480 481block migration (since 8.2) 482''''''''''''''''''''''''''' 483 484Block migration is too inflexible. It needs to migrate all block 485devices or none. 486 487Please see "QMP invocation for live storage migration with 488``blockdev-mirror`` + NBD" in docs/interop/live-block-operations.rst 489for a detailed explanation. 490 491old compression method (since 8.2) 492'''''''''''''''''''''''''''''''''' 493 494Compression method fails too much. Too many races. We are going to 495remove it if nobody fixes it. For starters, migration-test 496compression tests are disabled because they fail randomly. If you need 497compression, use multifd compression methods. 498