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 23Build options 24------------- 25 26``gprof`` builds (since 8.0) 27'''''''''''''''''''''''''''' 28 29The ``--enable-gprof`` configure setting relies on compiler 30instrumentation to gather its data which can distort the generated 31profile. As other non-instrumenting tools are available that give a 32more holistic view of the system with non-instrumented binaries we are 33deprecating the build option and no longer defend it in CI. The 34``--enable-gcov`` build option remains for analysis test case 35coverage. 36 37System emulator command line arguments 38-------------------------------------- 39 40``QEMU_AUDIO_`` environment variables and ``-audio-help`` (since 4.0) 41''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 42 43The ``-audiodev`` argument is now the preferred way to specify audio 44backend settings instead of environment variables. To ease migration to 45the new format, the ``-audiodev-help`` option can be used to convert 46the current values of the environment variables to ``-audiodev`` options. 47 48Creating sound card devices and vnc without ``audiodev=`` property (since 4.2) 49'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 50 51When not using the deprecated legacy audio config, each sound card 52should specify an ``audiodev=`` property. Additionally, when using 53vnc, you should specify an ``audiodev=`` property if you plan to 54transmit audio through the VNC protocol. 55 56Short-form boolean options (since 6.0) 57'''''''''''''''''''''''''''''''''''''' 58 59Boolean options such as ``share=on``/``share=off`` could be written 60in short form as ``share`` and ``noshare``. This is now deprecated 61and will cause a warning. 62 63``delay`` option for socket character devices (since 6.0) 64''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 65 66The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on`` 67rather than ``delay=off``. 68 69``-smp`` ("parameter=0" SMP configurations) (since 6.2) 70''''''''''''''''''''''''''''''''''''''''''''''''''''''' 71 72Specified CPU topology parameters must be greater than zero. 73 74In the SMP configuration, users should either provide a CPU topology 75parameter with a reasonable value (greater than zero) or just omit it 76and QEMU will compute the missing value. 77 78However, historically it was implicitly allowed for users to provide 79a parameter with zero value, which is meaningless and could also possibly 80cause unexpected results in the -smp parsing. So support for this kind of 81configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will 82be removed in the near future, users have to ensure that all the topology 83members described with -smp are greater than zero. 84 85Plugin argument passing through ``arg=<string>`` (since 6.1) 86'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 87 88Passing TCG plugins arguments through ``arg=`` is redundant is makes the 89command-line less readable, especially when the argument itself consist of a 90name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``. 91Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated 92as short-form boolean values, and passed to plugins as ``arg_name=on``. 93However, short-form booleans are deprecated and full explicit ``arg_name=on`` 94form is preferred. 95 96``-no-hpet`` (since 8.0) 97'''''''''''''''''''''''' 98 99The HPET setting has been turned into a machine property. 100Use ``-machine hpet=off`` instead. 101 102``-no-acpi`` (since 8.0) 103'''''''''''''''''''''''' 104 105The ``-no-acpi`` setting has been turned into a machine property. 106Use ``-machine acpi=off`` instead. 107 108``-async-teardown`` (since 8.1) 109''''''''''''''''''''''''''''''' 110 111Use ``-run-with async-teardown=on`` instead. 112 113``-chroot`` (since 8.1) 114''''''''''''''''''''''' 115 116Use ``-run-with chroot=dir`` instead. 117 118``-singlestep`` (since 8.1) 119''''''''''''''''''''''''''' 120 121The ``-singlestep`` option has been turned into an accelerator property, 122and given a name that better reflects what it actually does. 123Use ``-accel tcg,one-insn-per-tb=on`` instead. 124 125User-mode emulator command line arguments 126----------------------------------------- 127 128``-singlestep`` (since 8.1) 129''''''''''''''''''''''''''' 130 131The ``-singlestep`` option has been given a name that better reflects 132what it actually does. For both linux-user and bsd-user, use the 133new ``-one-insn-per-tb`` option instead. 134 135QEMU Machine Protocol (QMP) commands 136------------------------------------ 137 138``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8) 139''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 140 141Use argument ``id`` instead. 142 143``eject`` argument ``device`` (since 2.8) 144''''''''''''''''''''''''''''''''''''''''' 145 146Use argument ``id`` instead. 147 148``blockdev-change-medium`` argument ``device`` (since 2.8) 149'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 150 151Use argument ``id`` instead. 152 153``block_set_io_throttle`` argument ``device`` (since 2.8) 154''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 155 156Use argument ``id`` instead. 157 158``blockdev-add`` empty string argument ``backing`` (since 2.10) 159''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 160 161Use argument value ``null`` instead. 162 163``block-commit`` arguments ``base`` and ``top`` (since 3.1) 164''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 165 166Use arguments ``base-node`` and ``top-node`` instead. 167 168``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) 169'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 170 171Use the more generic commands ``block-export-add`` and ``block-export-del`` 172instead. As part of this deprecation, where ``nbd-server-add`` used a 173single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``. 174 175``query-qmp-schema`` return value member ``values`` (since 6.2) 176''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 177 178Member ``values`` in return value elements with meta-type ``enum`` is 179deprecated. Use ``members`` instead. 180 181``drive-backup`` (since 6.2) 182'''''''''''''''''''''''''''' 183 184Use ``blockdev-backup`` in combination with ``blockdev-add`` instead. 185This change primarily separates the creation/opening process of the backup 186target with explicit, separate steps. ``blockdev-backup`` uses mostly the 187same arguments as ``drive-backup``, except the ``format`` and ``mode`` 188options are removed in favor of using explicit ``blockdev-create`` and 189``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for 190details. 191 192Incorrectly typed ``device_add`` arguments (since 6.2) 193'''''''''''''''''''''''''''''''''''''''''''''''''''''' 194 195Due to shortcomings in the internal implementation of ``device_add``, QEMU 196incorrectly accepts certain invalid arguments: Any object or list arguments are 197silently ignored. Other argument types are not checked, but an implicit 198conversion happens, so that e.g. string values can be assigned to integer 199device properties or vice versa. 200 201This is a bug in QEMU that will be fixed in the future so that previously 202accepted incorrect commands will return an error. Users should make sure that 203all arguments passed to ``device_add`` are consistent with the documented 204property types. 205 206``StatusInfo`` member ``singlestep`` (since 8.1) 207'''''''''''''''''''''''''''''''''''''''''''''''' 208 209The ``singlestep`` member of the ``StatusInfo`` returned from the 210``query-status`` command is deprecated. This member has a confusing 211name and it never did what the documentation claimed or what its name 212suggests. We do not believe that anybody is actually using the 213information provided in this member. 214 215The information it reports is whether the TCG JIT is in "one 216instruction per translated block" mode (which can be set on the 217command line or via the HMP, but not via QMP). The information remains 218available via the HMP 'info jit' command. 219 220QEMU Machine Protocol (QMP) events 221---------------------------------- 222 223``MEM_UNPLUG_ERROR`` (since 6.2) 224'''''''''''''''''''''''''''''''''''''''''''''''''''''''' 225 226Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead. 227 228``vcpu`` trace events (since 8.1) 229''''''''''''''''''''''''''''''''' 230 231The ability to instrument QEMU helper functions with vCPU-aware trace 232points was removed in 7.0. However QMP still exposed the vcpu 233parameter. This argument has now been deprecated and the remaining 234remaining trace points that used it are selected just by name. 235 236Human Monitor Protocol (HMP) commands 237------------------------------------- 238 239``singlestep`` (since 8.1) 240'''''''''''''''''''''''''' 241 242The ``singlestep`` command has been replaced by the ``one-insn-per-tb`` 243command, which has the same behaviour but a less misleading name. 244 245Host Architectures 246------------------ 247 248BE MIPS (since 7.2) 249''''''''''''''''''' 250 251As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of 252MIPS moved out of support making it hard to maintain our 253cross-compilation CI tests of the architecture. As we no longer have 254CI coverage support may bitrot away before the deprecation process 255completes. The little endian variants of MIPS (both 32 and 64 bit) are 256still a supported host architecture. 257 258System emulation on 32-bit x86 hosts (since 8.0) 259'''''''''''''''''''''''''''''''''''''''''''''''' 260 261Support for 32-bit x86 host deployments is increasingly uncommon in mainstream 262OS distributions given the widespread availability of 64-bit x86 hardware. 263The QEMU project no longer considers 32-bit x86 support for system emulation to 264be an effective use of its limited resources, and thus intends to discontinue 265it. Since all recent x86 hardware from the past >10 years is capable of the 26664-bit x86 extensions, a corresponding 64-bit OS should be used instead. 267 268 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. 279 280``pc-i440fx-1.4`` up to ``pc-i440fx-1.7`` (since 7.0) 281''''''''''''''''''''''''''''''''''''''''''''''''''''' 282 283These old machine types are quite neglected nowadays and thus might have 284various pitfalls with regards to live migration. Use a newer machine type 285instead. 286 287 288Backend options 289--------------- 290 291Using non-persistent backing file with pmem=on (since 6.1) 292'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 293 294This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 295device. However enabling ``memory-backend-file.pmem`` option, when backing file 296is (a) not DAX capable or (b) not on a filesystem that support direct mapping 297of persistent memory, is not safe and may lead to data loss or corruption in case 298of host crash. 299Options are: 300 301 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 302 (without persistence guaranties) with backing file on non DAX storage 303 - move backing file to NVDIMM storage and keep ``pmem=on`` 304 (to have NVDIMM with persistence guaranties). 305 306Device options 307-------------- 308 309Emulated device options 310''''''''''''''''''''''' 311 312``-device virtio-blk,scsi=on|off`` (since 5.0) 313^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 314 315The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0 316and later do not support it because the virtio-scsi device was introduced for 317full SCSI support. Use virtio-scsi instead when SCSI passthrough is required. 318 319Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an 320alias. 321 322``-device nvme-ns,eui64-default=on|off`` (since 7.1) 323^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 324 325In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 326identifier that is not globally unique. If an EUI-64 identifier is required, the 327user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 328 329``-device nvme,use-intel-id=on|off`` (since 7.1) 330^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 331 332The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 333from Intel that was not properly allocated. Since version 5.2, the controller 334has used a properly allocated identifier. Deprecate the ``use-intel-id`` 335machine compatibility parameter. 336 337``-device cxl-type3,memdev=xxxx`` (since 8.0) 338^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 339 340The ``cxl-type3`` device initially only used a single memory backend. With 341the addition of volatile memory support, it is now necessary to distinguish 342between persistent and volatile memory backends. As such, memdev is deprecated 343in favor of persistent-memdev. 344 345``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1) 346^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 347 348The 9p ``proxy`` filesystem backend driver has been deprecated and will be 349removed (along with its proxy helper daemon) in a future version of QEMU. Please 350use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem 351backend, or alternatively consider deploying virtiofsd instead. 352 353The 9p ``proxy`` backend was originally developed as an alternative to the 9p 354``local`` backend. The idea was to enhance security by dispatching actual low 355level filesystem operations from 9p server (QEMU process) over to a separate 356process (the virtfs-proxy-helper binary). However this alternative never gained 357momentum. The proxy backend is much slower than the local backend, hasn't seen 358any development in years, and showed to be less secure, especially due to the 359fact that its helper daemon must be run as root, whereas with the local backend 360QEMU is typically run as unprivileged user and allows to tighten behaviour by 361mapping permissions et al by using its 'mapped' security model option. 362 363Nowadays it would make sense to reimplement the ``proxy`` backend by using 364QEMU's ``vhost`` feature, which would eliminate the high latency costs under 365which the 9p ``proxy`` backend currently suffers. However as of to date nobody 366has indicated plans for such kind of reimplementation unfortunately. 367 368 369Block device options 370'''''''''''''''''''' 371 372``"backing": ""`` (since 2.12) 373^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 374 375In order to prevent QEMU from automatically opening an image's backing 376chain, use ``"backing": null`` instead. 377 378``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 379^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 380 381Options for ``rbd`` should be specified according to its runtime options, 382like other block drivers. Legacy parsing of keyvalue pair encoded 383filenames is useful to open images with the old format for backing files; 384These image files should be updated to use the current format. 385 386Example of legacy encoding:: 387 388 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 389 390The above, converted to the current supported format:: 391 392 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 393 394``iscsi,password=xxx`` (since 8.0) 395^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 396 397Specifying the iSCSI password in plain text on the command line using the 398``password`` option is insecure. The ``password-secret`` option should be 399used instead, to refer to a ``--object secret...`` instance that provides 400a password via a file, or encrypted. 401 402Backwards compatibility 403----------------------- 404 405Runnability guarantee of CPU models (since 4.1) 406''''''''''''''''''''''''''''''''''''''''''''''' 407 408Previous versions of QEMU never changed existing CPU models in 409ways that introduced additional host software or hardware 410requirements to the VM. This allowed management software to 411safely change the machine type of an existing VM without 412introducing new requirements ("runnability guarantee"). This 413prevented CPU models from being updated to include CPU 414vulnerability mitigations, leaving guests vulnerable in the 415default configuration. 416 417The CPU model runnability guarantee won't apply anymore to 418existing CPU models. Management software that needs runnability 419guarantees must resolve the CPU model aliases using the 420``alias-of`` field returned by the ``query-cpu-definitions`` QMP 421command. 422 423While those guarantees are kept, the return value of 424``query-cpu-definitions`` will have existing CPU model aliases 425point to a version that doesn't break runnability guarantees 426(specifically, version 1 of those CPU models). In future QEMU 427versions, aliases will point to newer CPU model versions 428depending on the machine type, so management software must 429resolve CPU model aliases before starting a virtual machine. 430 431QEMU guest agent 432---------------- 433 434``--blacklist`` command line option (since 7.2) 435''''''''''''''''''''''''''''''''''''''''''''''' 436 437``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better 438wording for what this option does). The short form ``-b`` still stays 439the same and thus is the preferred way for scripts that should run with 440both, older and future versions of QEMU. 441 442``blacklist`` config file option (since 7.2) 443'''''''''''''''''''''''''''''''''''''''''''' 444 445The ``blacklist`` config file option has been renamed to ``block-rpcs`` 446(to be in sync with the renaming of the corresponding command line 447option). 448 449Migration 450--------- 451 452``skipped`` MigrationStats field (since 8.1) 453'''''''''''''''''''''''''''''''''''''''''''' 454 455``skipped`` field in Migration stats has been deprecated. It hasn't 456been used for more than 10 years. 457 458