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 14As a special exception to this general timeframe, rather than have an 15indefinite lifetime, versioned machine types are only intended to be 16supported for a period of 6 years, equivalent to 18 QEMU releases. All 17versioned machine types will be automatically marked deprecated after an 18initial 3 years (9 QEMU releases) has passed, and will then be deleted after 19a further 3 year period has passed. It is recommended that a deprecated 20machine type is only used for incoming migrations and restore of saved state, 21for pre-existing VM deployments. They should be scheduled for updating to a 22newer machine type during an appropriate service window. Newly deployed VMs 23should exclusively use a non-deprecated machine type, with use of the most 24recent version highly recommended. Non-versioned machine types follow the 25general feature deprecation policy. 26 27What follows is a list of all features currently marked as 28deprecated. 29 30System emulator command line arguments 31-------------------------------------- 32 33Short-form boolean options (since 6.0) 34'''''''''''''''''''''''''''''''''''''' 35 36Boolean options such as ``share=on``/``share=off`` could be written 37in short form as ``share`` and ``noshare``. This is now deprecated 38and will cause a warning. 39 40``delay`` option for socket character devices (since 6.0) 41''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 42 43The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on`` 44rather than ``delay=off``. 45 46Plugin argument passing through ``arg=<string>`` (since 6.1) 47'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 48 49Passing TCG plugins arguments through ``arg=`` is redundant is makes the 50command-line less readable, especially when the argument itself consist of a 51name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``. 52Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated 53as short-form boolean values, and passed to plugins as ``arg_name=on``. 54However, short-form booleans are deprecated and full explicit ``arg_name=on`` 55form is preferred. 56 57``-smp`` (Unsupported "parameter=1" SMP configurations) (since 9.0) 58''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 59 60Specified CPU topology parameters must be supported by the machine. 61 62In the SMP configuration, users should provide the CPU topology parameters that 63are supported by the target machine. 64 65However, historically it was allowed for users to specify the unsupported 66topology parameter as "1", which is meaningless. So support for this kind of 67configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is 68marked deprecated since 9.0, users have to ensure that all the topology members 69described with -smp are supported by the target machine. 70 71``-old-param`` option for booting Arm kernels via param_struct (since 10.0) 72''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 73 74The ``-old-param`` command line option is specific to Arm targets: 75it is used when directly booting a guest kernel to pass it the 76command line and other information via the old ``param_struct`` ABI, 77rather than the newer ATAGS or DTB mechanisms. This option was only 78ever needed to support ancient kernels on some old board types 79like the ``akita`` or ``terrier``; it has been deprecated in the 80kernel since 2001. None of the board types QEMU supports need 81``param_struct`` support, so this option has been deprecated and will 82be removed in a future QEMU version. 83 84User-mode emulator command line arguments 85----------------------------------------- 86 87``-p`` (since 9.0) 88'''''''''''''''''' 89 90The ``-p`` option pretends to control the host page size. However, 91it is not possible to change the host page size, and using the 92option only causes failures. 93 94QEMU Machine Protocol (QMP) commands 95------------------------------------ 96 97``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 98''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 99 100Use argument ``id`` instead. 101 102``eject`` argument ``device`` (since 2.8) 103''''''''''''''''''''''''''''''''''''''''' 104 105Use argument ``id`` instead. 106 107``blockdev-change-medium`` argument ``device`` (since 2.8) 108'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 109 110Use argument ``id`` instead. 111 112``block_set_io_throttle`` argument ``device`` (since 2.8) 113''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 114 115Use argument ``id`` instead. 116 117``blockdev-add`` empty string argument ``backing`` (since 2.10) 118''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 119 120Use argument value ``null`` instead. 121 122``block-commit`` arguments ``base`` and ``top`` (since 3.1) 123''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 124 125Use arguments ``base-node`` and ``top-node`` instead. 126 127``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 128'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 129 130Use the more generic commands ``block-export-add`` and ``block-export-del`` 131instead. As part of this deprecation, where ``nbd-server-add`` used a 132single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 133 134``query-qmp-schema`` return value member ``values`` (since 6.2) 135''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 136 137Member ``values`` in return value elements with meta-type ``enum`` is 138deprecated. Use ``members`` instead. 139 140``drive-backup`` (since 6.2) 141'''''''''''''''''''''''''''' 142 143Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 144This change primarily separates the creation/opening process of the backup 145target with explicit, separate steps. ``blockdev-backup`` uses mostly the 146same arguments as ``drive-backup``, except the ``format`` and ``mode`` 147options are removed in favor of using explicit ``blockdev-create`` and 148``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 149details. 150 151``query-migrationthreads`` (since 9.2) 152'''''''''''''''''''''''''''''''''''''' 153 154To be removed with no replacement, as it reports only a limited set of 155threads (for example, it only reports source side of multifd threads, 156without reporting any destination threads, or non-multifd source threads). 157For debugging purpose, please use ``-name $VM,debug-threads=on`` instead. 158 159Incorrectly typed ``device_add`` arguments (since 6.2) 160'''''''''''''''''''''''''''''''''''''''''''''''''''''' 161 162Due to shortcomings in the internal implementation of ``device_add``, QEMU 163incorrectly accepts certain invalid arguments: Any object or list arguments are 164silently ignored. Other argument types are not checked, but an implicit 165conversion happens, so that e.g. string values can be assigned to integer 166device properties or vice versa. 167 168This is a bug in QEMU that will be fixed in the future so that previously 169accepted incorrect commands will return an error. Users should make sure that 170all arguments passed to ``device_add`` are consistent with the documented 171property types. 172 173Host Architectures 174------------------ 175 176Big endian MIPS since 7.2; 32-bit little endian MIPS since 9.2 177'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 178 179As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 180MIPS moved out of support making it hard to maintain our 181cross-compilation CI tests of the architecture. As we no longer have 182CI coverage support may bitrot away before the deprecation process 183completes. 184 185Likewise, the little endian variant of 32 bit MIPS is not supported by 186Debian 13 ("Trixie") and newer. 187 18864 bit little endian MIPS is still a supported host architecture. 189 190System emulation on 32-bit x86 hosts (since 8.0) 191'''''''''''''''''''''''''''''''''''''''''''''''' 192 193Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 194OS distributions given the widespread availability of 64-bit x86 hardware. 195The QEMU project no longer considers 32-bit x86 support for system emulation to 196be an effective use of its limited resources, and thus intends to discontinue 197it. Since all recent x86 hardware from the past >10 years is capable of the 19864-bit x86 extensions, a corresponding 64-bit OS should be used instead. 199 200TCG Plugin support not enabled by default on 32-bit hosts (since 9.2) 201''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 202 203While it is still possible to enable TCG plugin support for 32-bit 204hosts there are a number of potential pitfalls when instrumenting 20564-bit guests. The plugin APIs typically pass most addresses as 206uint64_t but practices like encoding that address in a host pointer 207for passing as user-data will lose data. As most software analysis 208benefits from having plenty of host memory it seems reasonable to 209encourage users to use 64 bit builds of QEMU for analysis work 210whatever targets they are instrumenting. 211 212TCG Plugin support not enabled by default with TCI (since 9.2) 213'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 214 215While the TCG interpreter can interpret the TCG ops used by plugins it 216is going to be so much slower it wouldn't make sense for any serious 217instrumentation. Due to implementation differences there will also be 218anomalies in things like memory instrumentation. 219 22032-bit host operating systems (since 10.0) 221'''''''''''''''''''''''''''''''''''''''''' 222 223Keeping 32-bit host support alive is a substantial burden for the 224QEMU project. Thus QEMU will in future drop the support for all 22532-bit host systems. 226 227linux-user mode CPUs 228-------------------- 229 230iwMMXt emulation and the ``pxa`` CPUs (since 10.0) 231'''''''''''''''''''''''''''''''''''''''''''''''''' 232 233The ``pxa`` CPU family (``pxa250``, ``pxa255``, ``pxa260``, 234``pxa261``, ``pxa262``, ``pxa270-a0``, ``pxa270-a1``, ``pxa270``, 235``pxa270-b0``, ``pxa270-b1``, ``pxa270-c0``, ``pxa270-c5``) are no 236longer used in system emulation, because all the machine types which 237used these CPUs were removed in the QEMU 9.2 release. These CPUs can 238now only be used in linux-user mode, and to do that you would have to 239explicitly select one of these CPUs with the ``-cpu`` command line 240option or the ``QEMU_CPU`` environment variable. 241 242We don't believe that anybody is using the iwMMXt emulation, and we do 243not have any tests to validate it or any real hardware or similar 244known-good implementation to test against. GCC is in the process of 245dropping their support for iwMMXt codegen. These CPU types are 246therefore deprecated in QEMU, and will be removed in a future release. 247 248System emulator CPUs 249-------------------- 250 251``power5+`` and ``power7+`` CPU names (since 9.0) 252''''''''''''''''''''''''''''''''''''''''''''''''' 253 254The character "+" in device (and thus also CPU) names is not allowed 255in the QEMU object model anymore. ``power5+``, ``power5+_v2.1``, 256``power7+`` and ``power7+_v2.1`` are currently still supported via 257an alias, but for consistency these will get removed in a future 258release, too. Use ``power5p_v2.1`` and ``power7p_v2.1`` instead. 259 260``Sun-UltraSparc-IIIi+`` and ``Sun-UltraSparc-IV+`` CPU names (since 9.1) 261''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 262 263The character "+" in device (and thus also CPU) names is not allowed 264in the QEMU object model anymore. ``Sun-UltraSparc-IIIi+`` and 265``Sun-UltraSparc-IV+`` are currently still supported via a workaround, 266but for consistency these will get removed in a future release, too. 267Use ``Sun-UltraSparc-IIIi-plus`` and ``Sun-UltraSparc-IV-plus`` instead. 268 269System emulator machines 270------------------------ 271 272Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 273'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 274 275The ``dtb-kaslr-seed`` property on the ``virt`` board has been 276deprecated; use the new name ``dtb-randomness`` instead. The new name 277better reflects the way this property affects all random data within 278the device tree blob, not just the ``kaslr-seed`` node. 279 280PPC 405 ``ref405ep`` machine (since 9.1) 281'''''''''''''''''''''''''''''''''''''''' 282 283The ``ref405ep`` machine and PPC 405 CPU have no known users, firmware 284images are not available, OpenWRT dropped support in 2019, U-Boot in 2852017, Linux also is dropping support in 2024. It is time to let go of 286this ancient hardware and focus on newer CPUs and platforms. 287 288Big-Endian variants of MicroBlaze ``petalogix-ml605`` and ``xlnx-zynqmp-pmu`` machines (since 9.2) 289'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 290 291Both ``petalogix-ml605`` and ``xlnx-zynqmp-pmu`` were added for little endian 292CPUs. Big endian support is not tested. 293 294Backend options 295--------------- 296 297Using non-persistent backing file with pmem=on (since 6.1) 298'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 299 300This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 301device. However enabling ``memory-backend-file.pmem`` option, when backing file 302is (a) not DAX capable or (b) not on a filesystem that support direct mapping 303of persistent memory, is not safe and may lead to data loss or corruption in case 304of host crash. 305Options are: 306 307 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 308 (without persistence guaranties) with backing file on non DAX storage 309 - move backing file to NVDIMM storage and keep ``pmem=on`` 310 (to have NVDIMM with persistence guaranties). 311 312Device options 313-------------- 314 315Emulated device options 316''''''''''''''''''''''' 317 318``-device nvme-ns,eui64-default=on|off`` (since 7.1) 319^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 320 321In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 322identifier that is not globally unique. If an EUI-64 identifier is required, the 323user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 324 325``-device nvme,use-intel-id=on|off`` (since 7.1) 326^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 327 328The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 329from Intel that was not properly allocated. Since version 5.2, the controller 330has used a properly allocated identifier. Deprecate the ``use-intel-id`` 331machine compatibility parameter. 332 333``-device cxl-type3,memdev=xxxx`` (since 8.0) 334^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 335 336The ``cxl-type3`` device initially only used a single memory backend. With 337the addition of volatile memory support, it is now necessary to distinguish 338between persistent and volatile memory backends. As such, memdev is deprecated 339in favor of persistent-memdev. 340 341 342RISC-V CPU properties which start with capital 'Z' (since 8.2) 343^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 344 345All RISC-V CPU properties which start with capital 'Z' are being deprecated 346starting in 8.2. The reason is that they were wrongly added with capital 'Z' 347in the past. CPU properties were later added with lower-case names, which 348is the format we want to use from now on. 349 350Users which try to use these deprecated properties will receive a warning 351recommending to switch to their stable counterparts: 352 353- "Zifencei" should be replaced with "zifencei" 354- "Zicsr" should be replaced with "zicsr" 355- "Zihintntl" should be replaced with "zihintntl" 356- "Zihintpause" should be replaced with "zihintpause" 357- "Zawrs" should be replaced with "zawrs" 358- "Zfa" should be replaced with "zfa" 359- "Zfh" should be replaced with "zfh" 360- "Zfhmin" should be replaced with "zfhmin" 361- "Zve32f" should be replaced with "zve32f" 362- "Zve64f" should be replaced with "zve64f" 363- "Zve64d" should be replaced with "zve64d" 364 365``-device sd-card,spec_version=1`` (since 9.1) 366^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 367 368SD physical layer specification v2.00 supersedes the v1.10 one. 369v2.00 is the default since QEMU 3.0.0. 370 371Block device options 372'''''''''''''''''''' 373 374``"backing": ""`` (since 2.12) 375^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 376 377In order to prevent QEMU from automatically opening an image's backing 378chain, use ``"backing": null`` instead. 379 380``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 381^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 382 383Options for ``rbd`` should be specified according to its runtime options, 384like other block drivers. Legacy parsing of keyvalue pair encoded 385filenames is useful to open images with the old format for backing files; 386These image files should be updated to use the current format. 387 388Example of legacy encoding:: 389 390 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 391 392The above, converted to the current supported format:: 393 394 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 395 396``iscsi,password=xxx`` (since 8.0) 397^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 398 399Specifying the iSCSI password in plain text on the command line using the 400``password`` option is insecure. The ``password-secret`` option should be 401used instead, to refer to a ``--object secret...`` instance that provides 402a password via a file, or encrypted. 403 404``gluster`` backend (since 9.2) 405^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 406 407According to https://marc.info/?l=fedora-devel-list&m=171934833215726 408the GlusterFS development effectively ended. Unless the development 409gains momentum again, the QEMU project will remove the gluster backend 410in a future release. 411 412 413Character device options 414'''''''''''''''''''''''' 415 416Backend ``memory`` (since 9.0) 417^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 418 419``memory`` is a deprecated synonym for ``ringbuf``. 420 421``reconnect`` (since 9.2) 422^^^^^^^^^^^^^^^^^^^^^^^^^ 423 424The ``reconnect`` option only allows specifiying second granularity timeouts, 425which is not enough for all types of use cases, use ``reconnect-ms`` instead. 426 427 428Net device options 429'''''''''''''''''' 430 431Stream ``reconnect`` (since 9.2) 432^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 433 434The ``reconnect`` option only allows specifiying second granularity timeouts, 435which is not enough for all types of use cases, use ``reconnect-ms`` instead. 436 437VFIO device options 438''''''''''''''''''' 439 440``-device vfio-calxeda-xgmac`` (since 10.0) 441^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 442The vfio-calxeda-xgmac device allows to assign a host Calxeda Highbank 44310Gb XGMAC Ethernet controller device ("calxeda,hb-xgmac" compatibility 444string) to a guest. Calxeda HW has been ewasted now and there is no point 445keeping that device. 446 447``-device vfio-amd-xgbe`` (since 10.0) 448^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 449The vfio-amd-xgbe device allows to assign a host AMD 10GbE controller 450to a guest ("amd,xgbe-seattle-v1a" compatibility string). AMD "Seattle" 451is not supported anymore and there is no point keeping that device. 452 453``-device vfio-platform`` (since 10.0) 454^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 455The vfio-platform device allows to assign a host platform device 456to a guest in a generic manner. Integrating a new device into 457the vfio-platform infrastructure requires some adaptation at 458both kernel and qemu level. No such attempt has been done for years 459and the conclusion is that vfio-platform has not got any traction. 460PCIe passthrough shall be the mainline solution. 461 462CPU device properties 463''''''''''''''''''''' 464 465``pcommit`` on x86 (since 9.1) 466^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 467 468The PCOMMIT instruction was never included in any physical processor. 469It was implemented as a no-op instruction in TCG up to QEMU 9.0, but 470only with ``-cpu max`` (which does not guarantee migration compatibility 471across versions). 472 473``pmu-num=n`` on RISC-V CPUs (since 8.2) 474^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 475 476In order to support more flexible counter configurations this has been replaced 477by a ``pmu-mask`` property. If set of counters is continuous then the mask can 478be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 479must be left clear. 480 481 482Backwards compatibility 483----------------------- 484 485Runnability guarantee of CPU models (since 4.1) 486''''''''''''''''''''''''''''''''''''''''''''''' 487 488Previous versions of QEMU never changed existing CPU models in 489ways that introduced additional host software or hardware 490requirements to the VM. This allowed management software to 491safely change the machine type of an existing VM without 492introducing new requirements ("runnability guarantee"). This 493prevented CPU models from being updated to include CPU 494vulnerability mitigations, leaving guests vulnerable in the 495default configuration. 496 497The CPU model runnability guarantee won't apply anymore to 498existing CPU models. Management software that needs runnability 499guarantees must resolve the CPU model aliases using the 500``alias-of`` field returned by the ``query-cpu-definitions`` QMP 501command. 502 503While those guarantees are kept, the return value of 504``query-cpu-definitions`` will have existing CPU model aliases 505point to a version that doesn't break runnability guarantees 506(specifically, version 1 of those CPU models). In future QEMU 507versions, aliases will point to newer CPU model versions 508depending on the machine type, so management software must 509resolve CPU model aliases before starting a virtual machine. 510 511RISC-V "virt" board "riscv,delegate" DT property (since 9.1) 512'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 513 514The "riscv,delegate" DT property was added in QEMU 7.0 as part of 515the AIA APLIC support. The property changed name during the review 516process in Linux and the correct name ended up being 517"riscv,delegation". Changing the DT property name will break all 518available firmwares that are using the current (wrong) name. The 519property is kept as is in 9.1, together with "riscv,delegation", to 520give more time for firmware developers to change their code. 521 522Migration 523--------- 524 525``fd:`` URI when used for file migration (since 9.1) 526'''''''''''''''''''''''''''''''''''''''''''''''''''' 527 528The ``fd:`` URI can currently provide a file descriptor that 529references either a socket or a plain file. These are two different 530types of migration. In order to reduce ambiguity, the ``fd:`` URI 531usage of providing a file descriptor to a plain file has been 532deprecated in favor of explicitly using the ``file:`` URI with the 533file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` 534command documentation for details on the ``fdset`` usage. 535 536``zero-blocks`` capability (since 9.2) 537'''''''''''''''''''''''''''''''''''''' 538 539The ``zero-blocks`` capability was part of the block migration which 540doesn't exist anymore since it was removed in QEMU v9.1. 541