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 250Backend options 251--------------- 252 253Using non-persistent backing file with pmem=on (since 6.1) 254'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 255 256This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 257device. However enabling ``memory-backend-file.pmem`` option, when backing file 258is (a) not DAX capable or (b) not on a filesystem that support direct mapping 259of persistent memory, is not safe and may lead to data loss or corruption in case 260of host crash. 261Options are: 262 263 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 264 (without persistence guaranties) with backing file on non DAX storage 265 - move backing file to NVDIMM storage and keep ``pmem=on`` 266 (to have NVDIMM with persistence guaranties). 267 268Device options 269-------------- 270 271Emulated device options 272''''''''''''''''''''''' 273 274``-device virtio-blk,scsi=on|off`` (since 5.0) 275^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 276 277The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 278and later do not support it because the virtio-scsi device was introduced for 279full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 280 281Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 282alias. 283 284``-device nvme-ns,eui64-default=on|off`` (since 7.1) 285^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 286 287In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 288identifier that is not globally unique. If an EUI-64 identifier is required, the 289user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 290 291``-device nvme,use-intel-id=on|off`` (since 7.1) 292^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 293 294The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 295from Intel that was not properly allocated. Since version 5.2, the controller 296has used a properly allocated identifier. Deprecate the ``use-intel-id`` 297machine compatibility parameter. 298 299``-device cxl-type3,memdev=xxxx`` (since 8.0) 300^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 301 302The ``cxl-type3`` device initially only used a single memory backend. With 303the addition of volatile memory support, it is now necessary to distinguish 304between persistent and volatile memory backends. As such, memdev is deprecated 305in favor of persistent-memdev. 306 307``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 308^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 309 310The 9p ``proxy`` filesystem backend driver has been deprecated and will be 311removed (along with its proxy helper daemon) in a future version of QEMU. Please 312use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 313backend, or alternatively consider deploying virtiofsd instead. 314 315The 9p ``proxy`` backend was originally developed as an alternative to the 9p 316``local`` backend. The idea was to enhance security by dispatching actual low 317level filesystem operations from 9p server (QEMU process) over to a separate 318process (the virtfs-proxy-helper binary). However this alternative never gained 319momentum. The proxy backend is much slower than the local backend, hasn't seen 320any development in years, and showed to be less secure, especially due to the 321fact that its helper daemon must be run as root, whereas with the local backend 322QEMU is typically run as unprivileged user and allows to tighten behaviour by 323mapping permissions et al by using its 'mapped' security model option. 324 325Nowadays it would make sense to reimplement the ``proxy`` backend by using 326QEMU's ``vhost`` feature, which would eliminate the high latency costs under 327which the 9p ``proxy`` backend currently suffers. However as of to date nobody 328has indicated plans for such kind of reimplementation unfortunately. 329 330RISC-V 'any' CPU type ``-cpu any`` (since 8.2) 331^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 332 333The 'any' CPU type was introduced back in 2018 and has been around since the 334initial RISC-V QEMU port. Its usage has always been unclear: users don't know 335what to expect from a CPU called 'any', and in fact the CPU does not do anything 336special that isn't already done by the default CPUs rv32/rv64. 337 338After the introduction of the 'max' CPU type, RISC-V now has a good coverage 339of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete 340CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any' 341CPU type starting in 8.2. 342 343RISC-V CPU properties which start with capital 'Z' (since 8.2) 344^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 345 346All RISC-V CPU properties which start with capital 'Z' are being deprecated 347starting in 8.2. The reason is that they were wrongly added with capital 'Z' 348in the past. CPU properties were later added with lower-case names, which 349is the format we want to use from now on. 350 351Users which try to use these deprecated properties will receive a warning 352recommending to switch to their stable counterparts: 353 354- "Zifencei" should be replaced with "zifencei" 355- "Zicsr" should be replaced with "zicsr" 356- "Zihintntl" should be replaced with "zihintntl" 357- "Zihintpause" should be replaced with "zihintpause" 358- "Zawrs" should be replaced with "zawrs" 359- "Zfa" should be replaced with "zfa" 360- "Zfh" should be replaced with "zfh" 361- "Zfhmin" should be replaced with "zfhmin" 362- "Zve32f" should be replaced with "zve32f" 363- "Zve64f" should be replaced with "zve64f" 364- "Zve64d" should be replaced with "zve64d" 365 366``-device pvrdma`` and the rdma subsystem (since 8.2) 367^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 368 369The pvrdma device and the whole rdma subsystem are in a bad shape and 370without active maintenance. The QEMU project intends to remove this 371device and subsystem from the code base in a future release without 372replacement unless somebody steps up and improves the situation. 373 374 375Block device options 376'''''''''''''''''''' 377 378``"backing": ""`` (since 2.12) 379^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 380 381In order to prevent QEMU from automatically opening an image's backing 382chain, use ``"backing": null`` instead. 383 384``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 385^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 386 387Options for ``rbd`` should be specified according to its runtime options, 388like other block drivers. Legacy parsing of keyvalue pair encoded 389filenames is useful to open images with the old format for backing files; 390These image files should be updated to use the current format. 391 392Example of legacy encoding:: 393 394 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 395 396The above, converted to the current supported format:: 397 398 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 399 400``iscsi,password=xxx`` (since 8.0) 401^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 402 403Specifying the iSCSI password in plain text on the command line using the 404``password`` option is insecure. The ``password-secret`` option should be 405used instead, to refer to a ``--object secret...`` instance that provides 406a password via a file, or encrypted. 407 408Backwards compatibility 409----------------------- 410 411Runnability guarantee of CPU models (since 4.1) 412''''''''''''''''''''''''''''''''''''''''''''''' 413 414Previous versions of QEMU never changed existing CPU models in 415ways that introduced additional host software or hardware 416requirements to the VM. This allowed management software to 417safely change the machine type of an existing VM without 418introducing new requirements ("runnability guarantee"). This 419prevented CPU models from being updated to include CPU 420vulnerability mitigations, leaving guests vulnerable in the 421default configuration. 422 423The CPU model runnability guarantee won't apply anymore to 424existing CPU models. Management software that needs runnability 425guarantees must resolve the CPU model aliases using the 426``alias-of`` field returned by the ``query-cpu-definitions`` QMP 427command. 428 429While those guarantees are kept, the return value of 430``query-cpu-definitions`` will have existing CPU model aliases 431point to a version that doesn't break runnability guarantees 432(specifically, version 1 of those CPU models). In future QEMU 433versions, aliases will point to newer CPU model versions 434depending on the machine type, so management software must 435resolve CPU model aliases before starting a virtual machine. 436 437QEMU guest agent 438---------------- 439 440``--blacklist`` command line option (since 7.2) 441''''''''''''''''''''''''''''''''''''''''''''''' 442 443``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 444wording for what this option does). The short form ``-b`` still stays 445the same and thus is the preferred way for scripts that should run with 446both, older and future versions of QEMU. 447 448``blacklist`` config file option (since 7.2) 449'''''''''''''''''''''''''''''''''''''''''''' 450 451The ``blacklist`` config file option has been renamed to ``block-rpcs`` 452(to be in sync with the renaming of the corresponding command line 453option). 454 455Migration 456--------- 457 458``skipped`` MigrationStats field (since 8.1) 459'''''''''''''''''''''''''''''''''''''''''''' 460 461``skipped`` field in Migration stats has been deprecated. It hasn't 462been used for more than 10 years. 463 464