Features/LegacyRemoval
Problem description
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.
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 this wiki page, and that there have to be at least two public releases of QEMU where the interface still works, but issues a warning when used. 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 not be removed. The warning should say that the interface is deprecated / going away soon, with a pointer to documentation or similar information about its replacement syntax.
Deprecated command line parameters
| Parameter | Rationale | Deprecated in | Removal in |
|---|---|---|---|
| -net channel | Replaced by "-netdev user,guestfwd=..."
(and is even not documented, i.e. hardly used in the wild) |
v2.6.0 | v3.0.0 |
| -net dump | Replaced by "-object filter-dump,..." | v2.10.0 | v3.0.0 |
| -smb | Replaced by "-netdev user,smb=..." | v2.6.0 | v3.0.0 |
| -tftp | Replaced by "-netdev user,tftp=..." | v2.6.0 | v3.0.0 |
| -bootp | Replaced by "-netdev user,bootfile=..." | v2.6.0 | v3.0.0 |
| -redir | Replaced by "-netdev user,hostfwd=..." | v2.6.0 | v3.0.0 |
| -hdachs | Replaced by options on "-device" | v2.10.0 | v3.0.0 |
| -drive boot= | Dummy legacy option from qemu-kvm | v1.3.0 | v3.0.0 |
| -no-kvm-pit | Dummy legacy option from qemu-kvm | v1.3.0 | v3.0.0 |
| -no-kvm-pit-reinjection | Legacy option from qemu-kvm | v1.3.0 | v3.0.0 |
| -tdf | Dummy legacy option from qemu-kvm | v1.3.0 | v3.0.0 |
| -usbdevice | Replaced by the generic -device parameter | v2.10.0 | v3.0.0 |
| -drive serial= -drive trans= -drive secs= -drive heads= -drive cyls= -drive addr= |
Replaced by options on "-device". | v2.10.0 | v3.0.0 |
Future candidates
| Parameter | Rationale |
|---|---|
| -net | Replaced by "-netdev id=netdev0 -device e1000,netdev=netdev0". There are several loose ends: what about machine type built-in NICs that use nd_table[]? Can vlan command-line options be removed in some places? |
| -netdev hubport | Should be removed in line with the 'vlan' concept of the -net parameter |
| -drive 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 |
| -no-kvm | Not necessary anymore, TCG is default |
| -localtime | Undocumented. Replace by -rtc base=localtime |
| -startdate | Undocumented. Replaced by -rtc option |
| -clock | Silently ignored for compatibility |
Deprecated qemu-img parameters
| Parameter | Rationale | Deprecated in | Removal in |
|---|---|---|---|
| snapshot_id_or_name | Use snapshot_param instead | v2.0.0 | v3.0.0 |
| -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 | v3.0.0 |
| -e | -o encryption | v0.14 | v2.10.0 |
| -6 | -o compat6 | v0.14 | v2.10.0 |
Deprecated HMP commands
| Parameter | Rationale | Deprecated in | Removal in |
|---|---|---|---|
| usb_add, usb_remove | Replaced by "device_add" and "device_del" | v2.10.0 | v3.0.0 |
| host_net_add, host_net_remove | Replaced by "netdev_add" and "netdev_del" | v2.10.0 | v3.0.0 |
Future candidates
| Parameter | Rationale |
|---|---|
| migrate_set_downtime, migrate_set_speed | Replaced by "migrate_set_parameter" since v2.8 |
Deprecated machines
Future candidates
| Machine | Rationale |
|---|---|
| prep (ppc) | Obsoleted by the "40p" machine |
| isapc (x86) | guests should be able to use "pc" instead (but firmware code paths would be different, do we care?) |
| pc-0.10 and pc-0.11 | Oldest QEMU version that is likely still used in the wild is 0.12 (CentOS 6) |
Deprecated devices
| Device | Rationale | Deprecated in | Removal in |
|---|---|---|---|
| spapr-pci-vfio-host-bridge | See commit 72700d7e733948fa | v2.6.0 | v3.0.0 |
| ide-device | Replaced by "ide-cd" and "ide-hd" | v0.15.0 | v3.0.0 ? |
| scsi-disk | Replaced by "scsi-cd" and "scsi-hd" | v0.15.0 | v3.0.0 ? |
Future candidates
| Machine | 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:
- AIX as host OS
- Solaris as host OS
- The Itanium ia64 TCG backend
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)