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 269PPC 405 CPUs (since 10.0) 270''''''''''''''''''''''''' 271 272The PPC 405 CPU has no known users and the ``ref405ep`` machine was 273removed in QEMU 10.0. Since the IBM POWER [8-11] processors uses an 274embedded 405 for power management (OCC) and other internal tasks, it 275is theoretically possible to use QEMU to model them. Let's keep the 276CPU implementation for a while before removing all support. 277 278System emulator machines 279------------------------ 280 281Versioned machine types (aarch64, arm, i386, m68k, ppc64, s390x, x86_64) 282'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 283 284In accordance with our versioned machine type deprecation policy, all machine 285types with version |VER_MACHINE_DEPRECATION_VERSION|, or older, have been 286deprecated. 287 288Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1) 289'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 290 291The ``dtb-kaslr-seed`` property on the ``virt`` board has been 292deprecated; use the new name ``dtb-randomness`` instead. The new name 293better reflects the way this property affects all random data within 294the device tree blob, not just the ``kaslr-seed`` node. 295 296Big-Endian variants of MicroBlaze ``petalogix-ml605`` and ``xlnx-zynqmp-pmu`` machines (since 9.2) 297'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 298 299Both ``petalogix-ml605`` and ``xlnx-zynqmp-pmu`` were added for little endian 300CPUs. Big endian support is not tested. 301 302Mips ``mipssim`` machine (since 10.0) 303''''''''''''''''''''''''''''''''''''' 304 305Linux dropped support for this virtual machine type in kernel v3.7, and 306there does not seem to be anybody around who is still using this board 307in QEMU: Most former MIPS-related people are working on other architectures 308in their everyday job nowadays, and we are also not aware of anybody still 309using old binaries with this board (i.e. there is also no binary available 310online to check that this board did not completely bitrot yet). It is 311recommended to use another MIPS machine for future MIPS code development 312instead. 313 314RISC-V default machine option (since 10.0) 315'''''''''''''''''''''''''''''''''''''''''' 316 317RISC-V defines ``spike`` as the default machine if no machine option is 318given in the command line. This happens because ``spike`` is the first 319RISC-V machine implemented in QEMU and setting it as default was 320convenient at that time. Now we have 7 riscv64 and 6 riscv32 machines 321and having ``spike`` as a default is no longer justified. This default 322will also promote situations where users think they're running ``virt`` 323(the most used RISC-V machine type in 10.0) when in fact they're 324running ``spike``. 325 326Removing the default machine option forces users to always set the machine 327they want to use and avoids confusion. Existing users of the ``spike`` 328machine must ensure that they're setting the ``spike`` machine in the 329command line (``-M spike``). 330 331 332Backend options 333--------------- 334 335Using non-persistent backing file with pmem=on (since 6.1) 336'''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 337 338This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM 339device. However enabling ``memory-backend-file.pmem`` option, when backing file 340is (a) not DAX capable or (b) not on a filesystem that support direct mapping 341of persistent memory, is not safe and may lead to data loss or corruption in case 342of host crash. 343Options are: 344 345 - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM 346 (without persistence guaranties) with backing file on non DAX storage 347 - move backing file to NVDIMM storage and keep ``pmem=on`` 348 (to have NVDIMM with persistence guaranties). 349 350Device options 351-------------- 352 353Emulated device options 354''''''''''''''''''''''' 355 356``-device nvme-ns,eui64-default=on|off`` (since 7.1) 357^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 358 359In QEMU versions 6.1, 6.2 and 7.0, the ``nvme-ns`` generates an EUI-64 360identifier that is not globally unique. If an EUI-64 identifier is required, the 361user must set it explicitly using the ``nvme-ns`` device parameter ``eui64``. 362 363``-device nvme,use-intel-id=on|off`` (since 7.1) 364^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 365 366The ``nvme`` device originally used a PCI Vendor/Device Identifier combination 367from Intel that was not properly allocated. Since version 5.2, the controller 368has used a properly allocated identifier. Deprecate the ``use-intel-id`` 369machine compatibility parameter. 370 371``-device cxl-type3,memdev=xxxx`` (since 8.0) 372^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 373 374The ``cxl-type3`` device initially only used a single memory backend. With 375the addition of volatile memory support, it is now necessary to distinguish 376between persistent and volatile memory backends. As such, memdev is deprecated 377in favor of persistent-memdev. 378 379 380RISC-V CPU properties which start with capital 'Z' (since 8.2) 381^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 382 383All RISC-V CPU properties which start with capital 'Z' are being deprecated 384starting in 8.2. The reason is that they were wrongly added with capital 'Z' 385in the past. CPU properties were later added with lower-case names, which 386is the format we want to use from now on. 387 388Users which try to use these deprecated properties will receive a warning 389recommending to switch to their stable counterparts: 390 391- "Zifencei" should be replaced with "zifencei" 392- "Zicsr" should be replaced with "zicsr" 393- "Zihintntl" should be replaced with "zihintntl" 394- "Zihintpause" should be replaced with "zihintpause" 395- "Zawrs" should be replaced with "zawrs" 396- "Zfa" should be replaced with "zfa" 397- "Zfh" should be replaced with "zfh" 398- "Zfhmin" should be replaced with "zfhmin" 399- "Zve32f" should be replaced with "zve32f" 400- "Zve64f" should be replaced with "zve64f" 401- "Zve64d" should be replaced with "zve64d" 402 403``-device sd-card,spec_version=1`` (since 9.1) 404^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 405 406SD physical layer specification v2.00 supersedes the v1.10 one. 407v2.00 is the default since QEMU 3.0.0. 408 409Block device options 410'''''''''''''''''''' 411 412``"backing": ""`` (since 2.12) 413^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 414 415In order to prevent QEMU from automatically opening an image's backing 416chain, use ``"backing": null`` instead. 417 418``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1) 419^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 420 421Options for ``rbd`` should be specified according to its runtime options, 422like other block drivers. Legacy parsing of keyvalue pair encoded 423filenames is useful to open images with the old format for backing files; 424These image files should be updated to use the current format. 425 426Example of legacy encoding:: 427 428 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"} 429 430The above, converted to the current supported format:: 431 432 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"} 433 434``iscsi,password=xxx`` (since 8.0) 435^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 436 437Specifying the iSCSI password in plain text on the command line using the 438``password`` option is insecure. The ``password-secret`` option should be 439used instead, to refer to a ``--object secret...`` instance that provides 440a password via a file, or encrypted. 441 442``gluster`` backend (since 9.2) 443^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 444 445According to https://marc.info/?l=fedora-devel-list&m=171934833215726 446the GlusterFS development effectively ended. Unless the development 447gains momentum again, the QEMU project will remove the gluster backend 448in a future release. 449 450 451Character device options 452'''''''''''''''''''''''' 453 454Backend ``memory`` (since 9.0) 455^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 456 457``memory`` is a deprecated synonym for ``ringbuf``. 458 459``reconnect`` (since 9.2) 460^^^^^^^^^^^^^^^^^^^^^^^^^ 461 462The ``reconnect`` option only allows specifying second granularity timeouts, 463which is not enough for all types of use cases, use ``reconnect-ms`` instead. 464 465 466Net device options 467'''''''''''''''''' 468 469Stream ``reconnect`` (since 9.2) 470^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 471 472The ``reconnect`` option only allows specifying second granularity timeouts, 473which is not enough for all types of use cases, use ``reconnect-ms`` instead. 474 475VFIO device options 476''''''''''''''''''' 477 478``-device vfio-calxeda-xgmac`` (since 10.0) 479^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 480The vfio-calxeda-xgmac device allows to assign a host Calxeda Highbank 48110Gb XGMAC Ethernet controller device ("calxeda,hb-xgmac" compatibility 482string) to a guest. Calxeda HW has been ewasted now and there is no point 483keeping that device. 484 485``-device vfio-amd-xgbe`` (since 10.0) 486^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 487The vfio-amd-xgbe device allows to assign a host AMD 10GbE controller 488to a guest ("amd,xgbe-seattle-v1a" compatibility string). AMD "Seattle" 489is not supported anymore and there is no point keeping that device. 490 491``-device vfio-platform`` (since 10.0) 492^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 493The vfio-platform device allows to assign a host platform device 494to a guest in a generic manner. Integrating a new device into 495the vfio-platform infrastructure requires some adaptation at 496both kernel and qemu level. No such attempt has been done for years 497and the conclusion is that vfio-platform has not got any traction. 498PCIe passthrough shall be the mainline solution. 499 500CPU device properties 501''''''''''''''''''''' 502 503``pcommit`` on x86 (since 9.1) 504^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 505 506The PCOMMIT instruction was never included in any physical processor. 507It was implemented as a no-op instruction in TCG up to QEMU 9.0, but 508only with ``-cpu max`` (which does not guarantee migration compatibility 509across versions). 510 511``pmu-num=n`` on RISC-V CPUs (since 8.2) 512^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 513 514In order to support more flexible counter configurations this has been replaced 515by a ``pmu-mask`` property. If set of counters is continuous then the mask can 516be calculated with ``((2 ^ n) - 1) << 3``. The least significant three bits 517must be left clear. 518 519 520Backwards compatibility 521----------------------- 522 523Runnability guarantee of CPU models (since 4.1) 524''''''''''''''''''''''''''''''''''''''''''''''' 525 526Previous versions of QEMU never changed existing CPU models in 527ways that introduced additional host software or hardware 528requirements to the VM. This allowed management software to 529safely change the machine type of an existing VM without 530introducing new requirements ("runnability guarantee"). This 531prevented CPU models from being updated to include CPU 532vulnerability mitigations, leaving guests vulnerable in the 533default configuration. 534 535The CPU model runnability guarantee won't apply anymore to 536existing CPU models. Management software that needs runnability 537guarantees must resolve the CPU model aliases using the 538``alias-of`` field returned by the ``query-cpu-definitions`` QMP 539command. 540 541While those guarantees are kept, the return value of 542``query-cpu-definitions`` will have existing CPU model aliases 543point to a version that doesn't break runnability guarantees 544(specifically, version 1 of those CPU models). In future QEMU 545versions, aliases will point to newer CPU model versions 546depending on the machine type, so management software must 547resolve CPU model aliases before starting a virtual machine. 548 549RISC-V "virt" board "riscv,delegate" DT property (since 9.1) 550'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 551 552The "riscv,delegate" DT property was added in QEMU 7.0 as part of 553the AIA APLIC support. The property changed name during the review 554process in Linux and the correct name ended up being 555"riscv,delegation". Changing the DT property name will break all 556available firmwares that are using the current (wrong) name. The 557property is kept as is in 9.1, together with "riscv,delegation", to 558give more time for firmware developers to change their code. 559 560Migration 561--------- 562 563``fd:`` URI when used for file migration (since 9.1) 564'''''''''''''''''''''''''''''''''''''''''''''''''''' 565 566The ``fd:`` URI can currently provide a file descriptor that 567references either a socket or a plain file. These are two different 568types of migration. In order to reduce ambiguity, the ``fd:`` URI 569usage of providing a file descriptor to a plain file has been 570deprecated in favor of explicitly using the ``file:`` URI with the 571file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` 572command documentation for details on the ``fdset`` usage. 573 574``zero-blocks`` capability (since 9.2) 575'''''''''''''''''''''''''''''''''''''' 576 577The ``zero-blocks`` capability was part of the block migration which 578doesn't exist anymore since it was removed in QEMU v9.1. 579