docs/about/deprecated.rst

   1 .. _Deprecated features:
   2
   3 Deprecated features
   4 ===================
   5
   6 In general features are intended to be supported indefinitely once
   7 introduced into QEMU. In the event that a feature needs to be removed,
   8 it will be listed in this section. The feature will remain functional for the
   9 release in which it was deprecated and one further release. After these two
  10 releases, the feature is liable to be removed. Deprecated features may also
  11 generate warnings on the console when QEMU starts up, or if activated via a
  12 monitor command, however, this is not a mandatory requirement.
  13
  14 Prior to the 2.10.0 release there was no official policy on how
  15 long features would be deprecated prior to their removal, nor
  16 any documented list of which features were deprecated. Thus
  17 any features deprecated prior to 2.10.0 will be treated as if
  18 they were first deprecated in the 2.10.0 release.
  19
  20 What follows is a list of all features currently marked as
  21 deprecated.
  22
  23 System emulator command line arguments
  24 --------------------------------------
  25
  26 Short-form boolean options (since 6.0)
  27 ''''''''''''''''''''''''''''''''''''''
  28
  29 Boolean options such as ``share=on``/``share=off`` could be written
  30 in short form as ``share`` and ``noshare``.  This is now deprecated
  31 and will cause a warning.
  32
  33 ``delay`` option for socket character devices (since 6.0)
  34 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
  35
  36 The replacement for the ``nodelay`` short-form boolean option is ``nodelay=on``
  37 rather than ``delay=off``.
  38
  39 ``-smp`` ("parameter=0" SMP configurations) (since 6.2)
  40 '''''''''''''''''''''''''''''''''''''''''''''''''''''''
  41
  42 Specified CPU topology parameters must be greater than zero.
  43
  44 In the SMP configuration, users should either provide a CPU topology
  45 parameter with a reasonable value (greater than zero) or just omit it
  46 and QEMU will compute the missing value.
  47
  48 However, historically it was implicitly allowed for users to provide
  49 a parameter with zero value, which is meaningless and could also possibly
  50 cause unexpected results in the -smp parsing. So support for this kind of
  51 configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will
  52 be removed in the near future, users have to ensure that all the topology
  53 members described with -smp are greater than zero.
  54
  55 Plugin argument passing through ``arg=<string>`` (since 6.1)
  56 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
  57
  58 Passing TCG plugins arguments through ``arg=`` is redundant is makes the
  59 command-line less readable, especially when the argument itself consist of a
  60 name and a value, e.g. ``-plugin plugin_name,arg="arg_name=arg_value"``.
  61 Therefore, the usage of ``arg`` is redundant. Single-word arguments are treated
  62 as short-form boolean values, and passed to plugins as ``arg_name=on``.
  63 However, short-form booleans are deprecated and full explicit ``arg_name=on``
  64 form is preferred.
  65
  66 ``-no-hpet`` (since 8.0)
  67 ''''''''''''''''''''''''
  68
  69 The HPET setting has been turned into a machine property.
  70 Use ``-machine hpet=off`` instead.
  71
  72 ``-no-acpi`` (since 8.0)
  73 ''''''''''''''''''''''''
  74
  75 The ``-no-acpi`` setting has been turned into a machine property.
  76 Use ``-machine acpi=off`` instead.
  77
  78 ``-async-teardown`` (since 8.1)
  79 '''''''''''''''''''''''''''''''
  80
  81 Use ``-run-with async-teardown=on`` instead.
  82
  83 ``-chroot`` (since 8.1)
  84 '''''''''''''''''''''''
  85
  86 Use ``-run-with chroot=dir`` instead.
  87
  88 ``-singlestep`` (since 8.1)
  89 '''''''''''''''''''''''''''
  90
  91 The ``-singlestep`` option has been turned into an accelerator property,
  92 and given a name that better reflects what it actually does.
  93 Use ``-accel tcg,one-insn-per-tb=on`` instead.
  94
  95 User-mode emulator command line arguments
  96 -----------------------------------------
  97
  98 ``-singlestep`` (since 8.1)
  99 '''''''''''''''''''''''''''
 100
 101 The ``-singlestep`` option has been given a name that better reflects
 102 what it actually does. For both linux-user and bsd-user, use the
 103 new ``-one-insn-per-tb`` option instead.
 104
 105 QEMU Machine Protocol (QMP) commands
 106 ------------------------------------
 107
 108 ``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8)
 109 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 110
 111 Use argument ``id`` instead.
 112
 113 ``eject`` argument ``device`` (since 2.8)
 114 '''''''''''''''''''''''''''''''''''''''''
 115
 116 Use argument ``id`` instead.
 117
 118 ``blockdev-change-medium`` argument ``device`` (since 2.8)
 119 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 120
 121 Use argument ``id`` instead.
 122
 123 ``block_set_io_throttle`` argument ``device`` (since 2.8)
 124 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 125
 126 Use argument ``id`` instead.
 127
 128 ``blockdev-add`` empty string argument ``backing`` (since 2.10)
 129 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 130
 131 Use argument value ``null`` instead.
 132
 133 ``block-commit`` arguments ``base`` and ``top`` (since 3.1)
 134 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 135
 136 Use arguments ``base-node`` and ``top-node`` instead.
 137
 138 ``nbd-server-add`` and ``nbd-server-remove`` (since 5.2)
 139 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 140
 141 Use the more generic commands ``block-export-add`` and ``block-export-del``
 142 instead.  As part of this deprecation, where ``nbd-server-add`` used a
 143 single ``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
 148 Member ``values`` in return value elements with meta-type ``enum`` is
 149 deprecated.  Use ``members`` instead.
 150
 151 ``drive-backup`` (since 6.2)
 152 ''''''''''''''''''''''''''''
 153
 154 Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
 155 This change primarily separates the creation/opening process of the backup
 156 target with explicit, separate steps. ``blockdev-backup`` uses mostly the
 157 same arguments as ``drive-backup``, except the ``format`` and ``mode``
 158 options are removed in favor of using explicit ``blockdev-create`` and
 159 ``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
 160 details.
 161
 162 Incorrectly typed ``device_add`` arguments (since 6.2)
 163 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
 164
 165 Due to shortcomings in the internal implementation of ``device_add``, QEMU
 166 incorrectly accepts certain invalid arguments: Any object or list arguments are
 167 silently ignored. Other argument types are not checked, but an implicit
 168 conversion happens, so that e.g. string values can be assigned to integer
 169 device properties or vice versa.
 170
 171 This is a bug in QEMU that will be fixed in the future so that previously
 172 accepted incorrect commands will return an error. Users should make sure that
 173 all arguments passed to ``device_add`` are consistent with the documented
 174 property types.
 175
 176 ``StatusInfo`` member ``singlestep`` (since 8.1)
 177 ''''''''''''''''''''''''''''''''''''''''''''''''
 178
 179 The ``singlestep`` member of the ``StatusInfo`` returned from the
 180 ``query-status`` command is deprecated. This member has a confusing
 181 name and it never did what the documentation claimed or what its name
 182 suggests. We do not believe that anybody is actually using the
 183 information provided in this member.
 184
 185 The information it reports is whether the TCG JIT is in "one
 186 instruction per translated block" mode (which can be set on the
 187 command line or via the HMP, but not via QMP). The information remains
 188 available via the HMP 'info jit' command.
 189
 190 QEMU Machine Protocol (QMP) events
 191 ----------------------------------
 192
 193 ``MEM_UNPLUG_ERROR`` (since 6.2)
 194 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 195
 196 Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.
 197
 198 ``vcpu`` trace events (since 8.1)
 199 '''''''''''''''''''''''''''''''''
 200
 201 The ability to instrument QEMU helper functions with vCPU-aware trace
 202 points was removed in 7.0. However QMP still exposed the vcpu
 203 parameter. This argument has now been deprecated and the remaining
 204 remaining trace points that used it are selected just by name.
 205
 206 Human Monitor Protocol (HMP) commands
 207 -------------------------------------
 208
 209 ``singlestep`` (since 8.1)
 210 ''''''''''''''''''''''''''
 211
 212 The ``singlestep`` command has been replaced by the ``one-insn-per-tb``
 213 command, which has the same behaviour but a less misleading name.
 214
 215 Host Architectures
 216 ------------------
 217
 218 BE MIPS (since 7.2)
 219 '''''''''''''''''''
 220
 221 As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
 222 MIPS moved out of support making it hard to maintain our
 223 cross-compilation CI tests of the architecture. As we no longer have
 224 CI coverage support may bitrot away before the deprecation process
 225 completes. The little endian variants of MIPS (both 32 and 64 bit) are
 226 still a supported host architecture.
 227
 228 System emulation on 32-bit x86 hosts (since 8.0)
 229 ''''''''''''''''''''''''''''''''''''''''''''''''
 230
 231 Support for 32-bit x86 host deployments is increasingly uncommon in mainstream
 232 OS distributions given the widespread availability of 64-bit x86 hardware.
 233 The QEMU project no longer considers 32-bit x86 support for system emulation to
 234 be an effective use of its limited resources, and thus intends to discontinue
 235 it. Since all recent x86 hardware from the past >10 years is capable of the
 236 64-bit x86 extensions, a corresponding 64-bit OS should be used instead.
 237
 238
 239 System emulator machines
 240 ------------------------
 241
 242 Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
 243 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 244
 245 The ``dtb-kaslr-seed`` property on the ``virt`` board has been
 246 deprecated; use the new name ``dtb-randomness`` instead. The new name
 247 better reflects the way this property affects all random data within
 248 the device tree blob, not just the ``kaslr-seed`` node.
 249
 250 Backend options
 251 ---------------
 252
 253 Using non-persistent backing file with pmem=on (since 6.1)
 254 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 255
 256 This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
 257 device. However enabling ``memory-backend-file.pmem`` option, when backing file
 258 is (a) not DAX capable or (b) not on a filesystem that support direct mapping
 259 of persistent memory, is not safe and may lead to data loss or corruption in case
 260 of host crash.
 261 Options 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
 268 Device options
 269 --------------
 270
 271 Emulated device options
 272 '''''''''''''''''''''''
 273
 274 ``-device virtio-blk,scsi=on|off`` (since 5.0)
 275 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 276
 277 The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature.  VIRTIO 1.0
 278 and later do not support it because the virtio-scsi device was introduced for
 279 full SCSI support.  Use virtio-scsi instead when SCSI passthrough is required.
 280
 281 Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
 282 alias.
 283
 284 ``-device nvme-ns,eui64-default=on|off`` (since 7.1)
 285 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 286
 287 In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64
 288 identifier that is not globally unique. If an EUI-64 identifier is required, the
 289 user 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
 294 The ``nvme`` device originally used a PCI Vendor/Device Identifier combination
 295 from Intel that was not properly allocated. Since version 5.2, the controller
 296 has used a properly allocated identifier. Deprecate the ``use-intel-id``
 297 machine compatibility parameter.
 298
 299 ``-device cxl-type3,memdev=xxxx`` (since 8.0)
 300 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 301
 302 The ``cxl-type3`` device initially only used a single memory backend.  With
 303 the addition of volatile memory support, it is now necessary to distinguish
 304 between persistent and volatile memory backends.  As such, memdev is deprecated
 305 in favor of persistent-memdev.
 306
 307 ``-fsdev proxy`` and ``-virtfs proxy`` (since 8.1)
 308 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 309
 310 The 9p ``proxy`` filesystem backend driver has been deprecated and will be
 311 removed (along with its proxy helper daemon) in a future version of QEMU. Please
 312 use ``-fsdev local`` or ``-virtfs local`` for using the 9p ``local`` filesystem
 313 backend, or alternatively consider deploying virtiofsd instead.
 314
 315 The 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
 317 level filesystem operations from 9p server (QEMU process) over to a separate
 318 process (the virtfs-proxy-helper binary). However this alternative never gained
 319 momentum. The proxy backend is much slower than the local backend, hasn't seen
 320 any development in years, and showed to be less secure, especially due to the
 321 fact that its helper daemon must be run as root, whereas with the local backend
 322 QEMU is typically run as unprivileged user and allows to tighten behaviour by
 323 mapping permissions et al by using its 'mapped' security model option.
 324
 325 Nowadays it would make sense to reimplement the ``proxy`` backend by using
 326 QEMU's ``vhost`` feature, which would eliminate the high latency costs under
 327 which the 9p ``proxy`` backend currently suffers. However as of to date nobody
 328 has indicated plans for such kind of reimplementation unfortunately.
 329
 330 ``-device pvrdma`` and the rdma subsystem (since 8.2)
 331 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 332
 333 The pvrdma device and the whole rdma subsystem are in a bad shape and
 334 without active maintenance. The QEMU project intends to remove this
 335 device and subsystem from the code base in a future release without
 336 replacement unless somebody steps up and improves the situation.
 337
 338
 339 Block device options
 340 ''''''''''''''''''''
 341
 342 ``"backing": ""`` (since 2.12)
 343 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 344
 345 In order to prevent QEMU from automatically opening an image's backing
 346 chain, use ``"backing": null`` instead.
 347
 348 ``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1)
 349 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 350
 351 Options for ``rbd`` should be specified according to its runtime options,
 352 like other block drivers.  Legacy parsing of keyvalue pair encoded
 353 filenames is useful to open images with the old format for backing files;
 354 These image files should be updated to use the current format.
 355
 356 Example of legacy encoding::
 357
 358   json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}
 359
 360 The above, converted to the current supported format::
 361
 362   json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
 363
 364 ``iscsi,password=xxx`` (since 8.0)
 365 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 366
 367 Specifying the iSCSI password in plain text on the command line using the
 368 ``password`` option is insecure. The ``password-secret`` option should be
 369 used instead, to refer to a ``--object secret...`` instance that provides
 370 a password via a file, or encrypted.
 371
 372 Backwards compatibility
 373 -----------------------
 374
 375 Runnability guarantee of CPU models (since 4.1)
 376 '''''''''''''''''''''''''''''''''''''''''''''''
 377
 378 Previous versions of QEMU never changed existing CPU models in
 379 ways that introduced additional host software or hardware
 380 requirements to the VM.  This allowed management software to
 381 safely change the machine type of an existing VM without
 382 introducing new requirements ("runnability guarantee").  This
 383 prevented CPU models from being updated to include CPU
 384 vulnerability mitigations, leaving guests vulnerable in the
 385 default configuration.
 386
 387 The CPU model runnability guarantee won't apply anymore to
 388 existing CPU models.  Management software that needs runnability
 389 guarantees must resolve the CPU model aliases using the
 390 ``alias-of`` field returned by the ``query-cpu-definitions`` QMP
 391 command.
 392
 393 While those guarantees are kept, the return value of
 394 ``query-cpu-definitions`` will have existing CPU model aliases
 395 point to a version that doesn't break runnability guarantees
 396 (specifically, version 1 of those CPU models).  In future QEMU
 397 versions, aliases will point to newer CPU model versions
 398 depending on the machine type, so management software must
 399 resolve CPU model aliases before starting a virtual machine.
 400
 401 QEMU guest agent
 402 ----------------
 403
 404 ``--blacklist`` command line option (since 7.2)
 405 '''''''''''''''''''''''''''''''''''''''''''''''
 406
 407 ``--blacklist`` has been replaced by ``--block-rpcs`` (which is a better
 408 wording for what this option does). The short form ``-b`` still stays
 409 the same and thus is the preferred way for scripts that should run with
 410 both, older and future versions of QEMU.
 411
 412 ``blacklist`` config file option (since 7.2)
 413 ''''''''''''''''''''''''''''''''''''''''''''
 414
 415 The ``blacklist`` config file option has been renamed to ``block-rpcs``
 416 (to be in sync with the renaming of the corresponding command line
 417 option).
 418
 419 Migration
 420 ---------
 421
 422 ``skipped`` MigrationStats field (since 8.1)
 423 ''''''''''''''''''''''''''''''''''''''''''''
 424
 425 ``skipped`` field in Migration stats has been deprecated.  It hasn't
 426 been used for more than 10 years.
 427