ChangeLog/2.0

System emulation

Incompatible changes to bus names

• All onboard buses now have distinct names. The following buses got renamed: i2c-bus.0 to i2c-bus.1 for machines n800, n810; virtio-mmio-bus.0 to virtio-mmio-bus.3 for vexpress-a15, vexpress-a9; virtio-mmio-bus.0 to virtio-mmio-bus.31 for virt; usb-bus.0 to usb-bus.1 for xilinx-zynq-a9, fulong2e; ide.0 to ide.1 for isapc, mips, g3beige, mac99, prep. Breaks migration. You can try to migrate from old to new by using bus=NEW rather bus=OLD on the destination.
• The root PCI bus on the pSeries machine is now called "pci.0" rather than "pci".

ARM

• Support for "-M virt", a board type that only uses virtio devices
• Support for "-cpu host" when running under KVM
• Support for new 32-bit mode ARMv8 instructions in TCG
• Support for AArch64 disassembling (requires a C++ compiler to be installed on the host)
• Initial support for KVM on AArch64 systems (some features such as migration are not yet implemented)
• Support for the Canon PowerShot A1100 DIGIC board using "-M canon-a1100"
• Support for the allwinner-a10-based board "-M cubieboard"
• Support for flow control in the Cadence UART

Power

• Support for Altivec 2.07 and VSX instructions when running under TCG
• Support for ISA 2.06 "load/store quadword instructions", "divide extended instructions" and "floating-point test instructions" when running under TCG
• PReP is not anymore (incorrectly) included in qemu-system-ppcemb
• Improved support for "-nodefaults" on the pSeries machine. Display devices created with "-device VGA" will be handled correctly in the device tree.

s390

• Support for adapter interrupts in virtio-cc2

SPARC

• Support for Sun CG3 framebuffer with the Sun4m machine. The CG3 framebuffer can be requested with "-vga cg3".
• Support for the CASA compare-and-swap instruction in TCG.

x86

• On the Q35 machine, the HPET interrupt can now be attached to GSIs 16-23, like on real hardware.
• The Q35 machine now supports CPU hotplug.
• Two flash chips can be specified using the "-drive if=pflash" or "-pflash" options twice.
• Memory layout has changed slightly; to improve performance, the PIIX4 machine ("-M pc") now has 3GB of low memory instead of 3.5GB if the guest has more than 3.5GB of memory. Similarly, the Q35 machine ("-M q35") now has 2GB instead of 2.75GB of low memory if the guest has more than 2.75GB of overall memory.
• Support for migration of Intel MPX registers.
• The Apple SMC device is now exposed in the ACPI tables.
• PCI hotplug now supports devices behind a bridge (only for bridges not added by hotplug; hot-plugged bridges can still use the PCI Standard Hot-Plug Controller).
• Support for the Hyper-V reference time counter via the "hv-time" suboption of "-cpu". This can improve performance of Windows guests substantially for applications that do many floating-point or SIMD operations. (Requires KVM and Linux 3.14).
• The distributed qemupciserial.inf file now allows installing multiport PCI serial devices on Windows too.

KVM

• x2apic is now enabled by default when KVM is in use.

Xen

• PCI passthrough of devices with a ROM now works.

Xtensa

• added support for ML605 and KC705 FPGA boards.
• Cache-related opcodes now correctly check privilege level/memory accessibility.

Device emulation

SCSI

• the SCSI layer can offload the WRITE SAME command to the host storage. This is supported on XFS file systems, raw devices, and iSCSI targets.
• SCSI disks can report a port WWN and port index, to make them look more like "real" SAS disks

USB

• support for suspend-to-RAM in the XHCI controller
• support for Microsoft descriptors, to make Windows use remote suspend by default.

GUI

• Windows hosts support keyboard translation in the GTK+ interface
• Support for SDL 2.0.

VNC

• setting the password via monitor command will not enable password auth as side effect any more. Use "qemu -vnc ${display},password" on the command line to enable password authentication.

GTK+

• Support for mouse wheel.

Monitor

• New HMP command cpu-add for CPU hotplug
• New QMP commands object-add and object-del for generic object hotplug (enables virtio-rng hotplug)
• New HMP commands object_add and object_del for generic object hotplug
• Improved command-line completion for device_add and device_del (as well as the new commands object_add and object_del)
• dump-guest-memory can produce kdump compressed format.

Migration

• Various fixes for migration with qcow2 images. Migration with qcow2 images is now reliable.
• Reduction (or elimination) of guest stalls during migration
• RDMA migration is now activated with the "rdma:HOST:PORT" syntax (used to be "x-rdma:HOST:PORT")

Network

• New backend "netmap" on BSD systems

Block devices in system emulation

• Live snapshot merge (...-commit) can be used to merge the active layer of an image into one of the snapshots
• Live and offline snapshot merge ("commit") will resize the destination image if necessary.
• The iSCSI and Gluster backends support snapshot merge.
• "query-block-stats" provides statistics for all images in the chain of backing files
• node-name, query-named-block-nodes: external snapshot, resize, change password (???)
• Experimental support in virtio-blk for M:N threading model: if you specify x-dataplane=on, you can also create I/O threads with "-object iothread" and point virtio-blk devices to the desired iothread with the "x-iothread" property. Properties of the running iothreads can be queried with the QMP command "query-iothreads".

Various

• -name now supports a "debug-threads" suboption. With this option, QEMU will assign names to each threads in order to simplify debugging. Note that thread names do not constitute a stable API.
• Improved coverage for "make check".
• Lots of bugfixes reported by Coverity (mostly for non-x86 guests).

Block devices and tools

• Network block drivers (curl, iscsi, rbd, ssh, glusterfs) can be built as shared library modules with "--enable-modules" configure option.
• When the destination of "qemu-img convert" is a raw device, qemu-img can ask the host storage to "discard" it instead of writing zeroes
• "qemu-img convert" can be passed a "-S 0" option to create a fully allocated image
• "qemu-img convert" can use hints from the host storage to speed up the transfer
• "qemu-img convert", "qemu-img create", "qemu-img amend" support multiple occurrences of the "-o" command line option.
• The libcurl interface had bitrotted and has been fixed.
• A new "quorum" driver for redundant storage is supported.
• QEMU is able to operate even if the underlying storage requires the buffer size to be a 4K multiple. This is the case for 4K-native disks (with cache=none or when accessed through iscsi:// URLs) and some raw devices. When this happens, QEMU emulates unaligned accesses using read-modify-write cycles if necessary. On properly configured guests newer than ~2009 there should be no performance penalty.
• qemu-io supports command editing via readline
• Pseudo-protocols like blkdebug and blkverify can be nested arbitrarily
• Improved error messages for many operations
• QEMU can access NFSv3 shares directly from userspace using libnfs. The share must be configured to allow access from high-numbered ports

TCG

• Improvements to the TCG optimizer make it produce faster code
• QEMU can use getauxval to detect the host instruction set for PPC64, ARM, s390
• QEMU supports generating MOVBE, ANDN, instructions in the x86 backend
• Support for AArch64 disassembling (requires a C++ compiler to be installed on the host)

Tracing

• LTTng 2.x is now supported

User-mode emulation

• Support for AArch64 user-mode emulation, including all the user-accessible instructions except for the optional CRC and crypto extensions
• Target specific minimum kernel versions, --enable-uname-release configure parameter will be removed in next release.
• Support for timer system calls: timer_create, timer_settime, timer_gettime, timer_getoverrun and timer_delete.
• Support for accept4 socketcall
• Support for sendmmsg/recvmmesg system calls
• Bug fixes