Changelog:
System emulation
Incompatible changes
SPI flash devices "160s33b", "320s33b", "640s33b", "at25df041a", "at25df321a", "at25df641", "at25fs010", "at25fs040", "at26df081a", "at26df161a", "at26df321", "at26f004", "at45db081d", "en25f32", "en25p32", "en25p64", "en25q32b", "en25q64", "gd25q32", "gd25q64", "m25p05", "m25p10", "m25p128", "m25p16", "m25p20", "m25p32", "m25p40", "m25p64", "m25p80", "m25pe16", "m25pe20", "m25pe80", "m25px32", "m25px32-s0", "m25px32-s1", "m25px64", "m45pe10", "m45pe16", "m45pe80", "mx25l12805d", "mx25l12855e", "mx25l1606e", "mx25l2005a", "mx25l25635e", "mx25l25655e", "mx25l3205d", "mx25l4005a", "mx25l6405d", "mx25l8005", "n25q032", "n25q032a11", "n25q032a13", "n25q064", "n25q064a11", "n25q064a13", "n25q128", "n25q128a11", "n25q128a13", "n25q256a11", "n25q256a13", "s25fl016k", "s25fl064k", "s25fl129p0", "s25fl129p1", "s25fl256s0", "s25fl256s1", "s25fl512s", "s25sl004a", "s25sl008a", "s25sl016a", "s25sl032a", "s25sl032p", "s25sl064a", "s25sl064p", "s25sl12800", "s25sl12801", "s70fl01gs", "sst25vf016b", "sst25vf032b", "sst25vf040b", "sst25vf080b", "sst25wf010", "sst25wf020", "sst25wf040", "sst25wf512", "w25q256", "w25q32", "w25q32dw", "w25q64", "w25q80", "w25q80bl", "w25x10", "w25x16", "w25x20", "w25x32", "w25x40", "w25x64", "w25x80" connect to a backend explicitly named by a "drive" property instead of an implicit -drive if=mtd. This only affect devices created explicitly with -device; "-drive if=mtd" still works for SPI flash devices created by boards, so this should affect almost no one.
Support for the original qcow2 image encryption has been disabled entirely from the system emulators. While QEMU 2.3 attempted to keep it available in system emulators, a bug in the code has actually broken it since 2.4, and no one complained. Supported for the format remains available only in command line tools qemu-img, qemu-io, qemu-nbd to facilitate data liberation. It is recommended to use 'qemu-img convert' to convert qcow2 encrypted images to uncrypted ones. The new LUKS encryption driver can provide a secure replacement, and a future release may integrate luks into qcow2 natively.
Autoconverge is not considered experimental anymore; autoconverge-related commands do not have the "x-" prefix anymore.
The MIPS64R6-generic CPU model was renamed to I6400.
On Q35 machines, IOMMU are now enabled with "-device iommu" instead of "-machine iommu=on".
Future incompatible changes
Three options are using different names on the command line and in configuration file. In particular:
The "acpi" configuration file section matches command-line option "acpitable";
The "boot-opts" configuration file section matches command-line option "boot";
The "smp-opts" configuration file section matches command-line option "smp".
-readconfig will standardize on the name for the command line option.
Behavior of automatic calculation of SMP topology when some SMP topology options for -smp are omitted (sockets, cores, threads) will change in the future. If guest ABI needs to be preserved on upgrades while using the SMP topology options, users should either set set all options explicitly (sockets, cores, threads), or omit all of them.
Devices "allwinner-a10", "pc87312", "ssi-sd" will be configured with explicit properties instead of implicitly. This is unlikely to affect users.
QMP command blockdev-add is still a work in progress. It doesn't support all block drivers, it lacks a matching blockdev-del, and more. It might change incompatibly.
ARM
The "virt" machine type has support for NUMA.
We now implement an emulated GICv3 interrupt controller, which is supported by the "virt" board and can be enabled with "-machine gic-version=3". Note that many guest OSes do not correctly support a GICv3 without security extensions; if your guest is Linux it must include commit 7c9b973061 "irqchip/gic-v3: Configure all interrupts as non-secure Group-1" or a backport of that patch to one of the stable branches. UEFI and FreeBSD are also known to need similar bug fixes.With a GICv3 the "virt" board now supports TCG (emulated CPU) configurations with more than 8 vCPUs.
New Xilinx Zynq ZCU102 board (-M xlnx-zcu102).
Xilinx Zynq boards have experimental support for ARM Security Extensions.
Xilinx Zynq MP supports DisplayPort (graphics and audio) and DDC (used for EDID info).
i.MX6?
KVM
Xilinx Zynq boards support KVM on AArch64 hosts.
MIPS
Support for 10-bit ASIDs
The MIPS64R6-generic CPU model was renamed to I6400.
Initial GIC support
Support for IEE 754-2008
PowerPC
Many TCG fixes.
mac99 machine can now boot MacOS >= 9.1
pSeries
Significant performance improvements for the spapr-llan device.
Support for CPU hotplug.
Performance improvements for VFIO through dynamic DMA windows.
s390
Support for runtime instrumentation
The IPL firmware can boot from devices in subchannel sets > 0
Major refactoring and improvements of the s390x-specific PCI code
Optionally, zPCI specific 'uid' and 'fid' attributes may be provided
Guest-acknowledged hotunplug (rather than 'surprise removal' only)
bootindex support for IPL from SCSI devices
SPARC
Fix for sun4m Solaris 9 "Segmentation fault" regression (see bug #1588328)
x86
CPU hot-remove support based on generic device_add/device_del interface
support arbitrary CPU adding/removal
Limitation: 1st (boot) CPU isn't removable
KVM
Support for LMCE (local MCE) virtualization, which will require Linux 4.8. LMCE can be enabled through "-cpu model,lmce" on all CPUs as long as the kernel supports it.
Device emulation and assignment
ACPI
NVDIMM devices are now described in the ACPI tables and support labels.
new ACPI CPU hotplug MMIO interface since 2.7 machine types for PC/Q35
more than 255 CPUs support
CPU hot-remove support
Guest side CPU hotplug status notification via _OST events
Block devices
Removed dataplane blockers? (Fam)
New -device properties replacing -drive properties?
virtio-blk now supports multiqueue through a "num-queues" device property.
Network devices
New device e1000e for Intel 82574 NIC.
QEMU now includes iPXE ROMs for vmxnet3 devices.
SCSI
scsi-block now passes sense data correctly to the guest, so that it can support for example persistent reservations.
Support for passthrough of SCSI scanner.
PCI/PCIe
On Q35 machines, IOMMU are now enabled with "-device iommu" instead of "-machine iommu=on".
USB
Support for Xen paravirtualized USB
usb-bot and usb-uas now support hotplug.
VFIO
Support for device assignment of Intel integrated graphics devices.
The SR-IOV capability is now hidden to guests when passing through a physical function.
virtio
Initial reconnect support for vhost-user.
Support for busy polling on vhost-net devices ("-netdev tap,...,poll-us=n").
virtio-gpu multi-monitor fixes
virtio-gpu 2d live migration support
Character devices
QEMU for Windows: Fixed handling of files used for character devices – they are now truncated by default like on Linux.
TLS support
Support for overriding the TLS property, for example "-object tls-creds-x509,...,priority=NORMAL:-VERS-SSL3.0" disables SSL 3.0. This can be used both to use a non-standard weaker set of prioririties, or to enforce a stronger default for QEMU. The default priority can also be specified through "--tls-priority=VALUE" at configure time.
GUI
A new option "-machine graphics=on|off" lets you disable graphics in the VM like "-nographic" (e.g. OpenBIOS will use the serial port for boot messages) but without an implicit "-display none".
Monitor
new 'info hotpluggable-cpus' and corresponding 'query-hotpluggable-cpus' QMP commands
to list present/possible CPUs with properties necessary to add a CPU instance using device_add for a given '-smp ...' layout
supported by x86 and SPAPR softmmu targets
Migration
Autoconverge is not considered experimental anymore. Autoconverge-related commands do not have the "x-" prefix.
TODO: TLS support
Network
User-mode networking supports DHCPv6, RDNSS, DNS6 and link-local DNS addresses.
Socket networking in TCP mode can now run over IPv6. UDP and multicast modes do not support IPv6 yet.
Block devices and tools
New "bench" command in qemu-img .
The "write" command in qemu-io grew "-f" and "-z -u" options.
TODO: Block job ids?
TCG
Speed improvements around 20%.
Fixes for self-modifying code.
Tracing
TODO: dfilter
TODO: tracing for qemu-io, qemu-img and qemu-nbd
CLI options
'-cpu cpu-model,feat1=foo,...' acts as a set of '-global cpu-model-type.feat1=foo' options, which affects initial CPUs as well as all CPUs created with help of -device/device_add/cpu-add for a given cpu-model
doesn't apply to SPARC target which uses legacy -cpu semantics as its features haven't been converted to properties.
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