Features/LegacyRemoval: Difference between revisions

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Note: This page is used to gather ideas about deprecated features and interfaces, the lists here are by no means mandatory! For a list of features / interfaces that have really been deprecated, please visit https://qemu.weilnetz.de/doc/qemu-doc.html#Deprecated-features instead.
QEMU has a lot of interfaces (like command line options or HMP commands) and old features (like certain machine types) which are considered as deprecated since other more generic interfaces/features have been established instead. We cannot carry the old code around forever. But we also do not want to remove it immediately to give the users and upper layer software stacks (like libvirt) a chance to migrate to the new interfaces step by step.


=== Problem description ===
This page was used to gather ideas about such deprecated features and interfaces, which finally culminated in the official deprecation chapter of the QEMU documentation. Since this page here was quickly out of date afterwards, its content has been removed now. Please visit https://qemu-project.gitlab.io/qemu/about/deprecated.html for the current official list instead.


QEMU has a lot of interfaces (like command line options or HMP commands) and old features (like certain machine types) which are considered as deprecated since other more generic interfaces/features have been established instead. We likely don't want to carry the old code around forever. But we also do not want to remove it immediately to give the users and upper layer software stacks (like libvirt) a chance to migrate to the new interfaces step by step. So this page is about collecting information and ideas about which interfaces/features are considered as obsolete and when they should be removed.
For information about features that have already been removed, please consult the https://qemu-project.gitlab.io/qemu/about/removed-features.html page.
 
=== Rules for removing an interface ===
 
Before an interface can be removed, there needs to be a clear transition plan for doing so. This means it should be added to the deprecation chapter in the qemu-doc file (see link at the top of this page), and that there have to be at least two public releases of QEMU where the interface still works after it ha been deprecated. Two public releases are required so that the users have at least one development cycle to complain if they think that there is a good reason that the interface should <em>not</em> be removed. Ideally the code should also emit a warning that says that the feature / interface is deprecated / going away soon, with a pointer to documentation or similar information about its replacement syntax.
 
== Deprecated command line parameters ==
 
{| class="wikitable" border="1"
!  Parameter
!  Rationale
!  Deprecated in
!  Removed in
|-
| -net channel
| Replaced by "-netdev user,guestfwd=..."
(and is even not documented, i.e. hardly used in the wild)
| v2.6.0
| v2.12.0
|-
| -net dump
| Replaced by "-object filter-dump,..."
| v2.10.0
| v2.12.0
|-
| -smb
| Replaced by "-netdev user,smb=..."
| v2.6.0
| TBD
|-
| -tftp
| Replaced by "-netdev user,tftp=..."
| v2.6.0
| TBD
|-
| -bootp
| Replaced by "-netdev user,bootfile=..."
| v2.6.0
| TBD
|-
| -redir
| Replaced by "-netdev user,hostfwd=..."
| v2.6.0
| TBD
|-
| -tdf
| Dummy legacy option from qemu-kvm
| v1.3.0
| v2.12.0
|-
| -usbdevice
| Replaced by the generic -device parameter
| v2.10.0
| partly in v2.12.0
|-
| -mon ...,default=on
| The "default" parameter does nothing anymore
| v2.8.0
| v2.12.0
|-
| -hdachs
| Replaced by options on "-device"
| v2.10.0
| v2.12.0
|-
| -drive&nbsp;boot=
| Dummy legacy option from qemu-kvm
| v1.3.0
| v2.12.0
|-
| -drive&nbsp;serial=<br>-drive&nbsp;trans=<br>-drive&nbsp;secs=<br>-drive&nbsp;heads=<br>-drive&nbsp;cyls=<br>-drive&nbsp;addr=
| Replaced by options on "-device".
| v2.10.0
| v3.0
|-
| -localtime
| Undocumented. Replace by -rtc base=localtime
| v2.12.0
| TBD
|-
| -startdate
| Undocumented. Replaced by -rtc option
| v2.12.0
| TBD
|-
| -rtc-td-hack
| Replaced by -rtc option
| v2.12.0
| TBD
|-
| -no-kvm
| Not necessary anymore, TCG is default
| v1.3.0
| TBD
|-
| -no-kvm-irqchip
| Use "-machine kernel_irqchip=off" instead
| v1.3.0
| v3.0
|-
| -no-kvm-pit
| Dummy legacy option from qemu-kvm
| v1.3.0
| v2.12.0
|-
| -no-kvm-pit-reinjection
| Legacy option from qemu-kvm
| v1.3.0
| v3.0
|-
| -vnc&nbsp;…,tls=…
| Deprecated in favour of tls-creds
| v2.5.0
| TBD
|-
| -vnc&nbsp;…,x509=…
| Deprecated in favour of tls-creds
| v2.5.0
| TBD
|-
| -vnc&nbsp;…,x509verify=…
| Deprecated in favour of tls-creds
| v2.5.0
| TBD
|-
| -fsdev handle
| Use "-fsdev local" instead
| v2.12.0
| TBD
|-
| -clock
| Silently ignored for compatibility
| v3.0
| TBD
|}
 
=== Future candidates ===
 
{| class="wikitable" border="1"
!  Parameter
!  Rationale
|-
| -net
| Replaced by "-netdev id=netdev0 -device e1000,netdev=netdev0" or the new -nic option
|-
| -drive&nbsp;media=
| Replaced by parameter on -device
|-
| -drive
| Replaced by "-blockdev" and "-device". Need to check that all devices automatically created by machines are still configurable, and "-blockdev" also needs better documentation first.
|-
| -enable-kvm
| Use "-accel kvm" instead
|-
| -enable-hax
| Use "-accel hax" instead
|}
 
== Deprecated qemu-img parameters ==
 
{| class="wikitable" border="1"
!  Parameter
!  Rationale
!  Deprecated in
!  Removed in
|-
| snapshot_id_or_name
| Use snapshot_param instead
| v2.0.0
| TBD
|-
| -b <invalid-image>
| Old QEMU versions did not check the validity of the given backing file string in ''qemu-img create'' unless the backing file needed to be opened for getting its size. Such checks are wanted and need to be disabled explicitly with ''-u'' now if necessary.
| v2.10.0
| TBD
|-
| -e
| -o encryption
| v0.14
| v2.10.0
|-
| -6
| -o compat6
| v0.14
| v2.10.0
|}
 
== Deprecated HMP commands ==
 
{| class="wikitable" border="1"
!  Parameter
!  Rationale
!  Deprecated in
!  Removed in
|-
| usb_add, usb_remove
| Replaced by "device_add" and "device_del"
| v2.10.0
| v2.12.0
|-
| host_net_add, host_net_remove
| Replaced by "netdev_add" and "netdev_del"
| v2.10.0
| v2.12.0
|}
 
=== Future candidates ===
 
{| class="wikitable" border="1"
!  Parameter
!  Rationale
|-
| migrate_set_downtime, migrate_set_speed
| Replaced by "migrate_set_parameter" since v2.8
|}
 
== Deprecated machines ==
 
{| class="wikitable" border="1"
!  Machine
!  Rationale
!  Deprecated in
!  Removed in
|-
| xlnx-ep108
| The EP108 was an early access development board that is no longer used.
| v2.11
| v3.0
|-
| pc-0.10 and pc-0.11
| Oldest QEMU version that is likely still used in the wild is 0.12 (CentOS 6)
| v3.0
| TBD
|-
| prep (ppc)
| Obsoleted by the "40p" machine
| v3.1
| TBD
|}
 
=== Future candidates ===
 
{| class="wikitable" border="1"
!  Machine
!  Rationale
|-
| isapc (x86)
| It's still under discussion whether we should keep this machine or not. Guests should be able to use "pc" instead, but firmware and OS code paths would be different, and it helps to remind us that there is also a world without PCI / ACPI / APIC, so to a small degree, this machine is still useful.
|}
 
== Deprecated machine options ==
 
{| class="wikitable" border="1"
!  Option
!  Machine
!  Rationale
!  Deprecated in
!  Removed in
|-
| s390-squash-mcss
| s390-ccw-virtio
| Made obsolete by unrestricting cssids
| v2.12.0
| TBD
|}
 
== Deprecated devices ==
 
{| class="wikitable" border="1"
!  Device
!  Rationale
!  Deprecated in
!  Removed in
|-
| spapr-pci-vfio-host-bridge
| See commit [http://git.qemu-project.org/?p=qemu.git;a=commitdiff;h=72700d7e733948fa7fbb735ccdf2209931c88476 72700d7e733948fa]
| v2.6.0
| v2.12.0
|-
| ivshmem
| Replaced by either the "ivshmem-plain" or "ivshmem-doorbell"
| v2.6.0
| TBD
|-
| ide-device
| Replaced by "ide-cd" and "ide-hd"
| v0.15.0 ?
| TBD
|-
| scsi-disk
| Replaced by "scsi-cd" and "scsi-hd"
| v0.15.0 ?
| TBD
|}
 
=== Future candidates ===
 
{| class="wikitable" border="1"
!  Device
!  Rationale
|-
| isa-vga
| unused when isapc machine type goes away
|-
| isa-cirrus-vga
| unused when isapc machine type goes away
|-
| ne2k_isa
| unused when isapc machine type goes away
|}
 
Alternatively: drop media=cdrom, make ide-hd and scsi-hd synonyms for ide-disk and scsi-disk.
 
== Miscellaneous ==
 
Certain host OS / CPUs are currently unmaintained, and we've got no build machine available for those, so they are scheduled for removal:
 
* <s>AIX as host OS</s> (Removed in 2.11)
* <s>Solaris 9 as host OS</s> (Removed in 2.10)
* <s>The Itanium ia64 TCG backend</s> (Removed in 2.11)
 
We also might want to drop support for older versions of libraries that are needed for building QEMU:
 
* SDL 1.2 (since SDL 2.0 is established nowadays)
* GTK 2 (since GTK 3 is established nowadays)

Latest revision as of 10:45, 4 August 2021

QEMU has a lot of interfaces (like command line options or HMP commands) and old features (like certain machine types) which are considered as deprecated since other more generic interfaces/features have been established instead. We cannot carry the old code around forever. But we also do not want to remove it immediately to give the users and upper layer software stacks (like libvirt) a chance to migrate to the new interfaces step by step.

This page was used to gather ideas about such deprecated features and interfaces, which finally culminated in the official deprecation chapter of the QEMU documentation. Since this page here was quickly out of date afterwards, its content has been removed now. Please visit https://qemu-project.gitlab.io/qemu/about/deprecated.html for the current official list instead.

For information about features that have already been removed, please consult the https://qemu-project.gitlab.io/qemu/about/removed-features.html page.

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