QEMU

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QEMU

Internet Explorer running on Windows XP running in QEMU running on Debian GNU/Linux
Developer: Fabrice Bellard
Latest release: 0.9.0 / February 5, 2007
OS: Windows, Solaris, Linux, FreeBSD, Mac OS X
Use: Emulator
License: Various
Website: www.qemu.com

QEMU is free software written by Fabrice Bellard that implements a fast processor emulator, allowing full virtualization of a PC system within another one. QEMU is a hypervisor and is similar to projects such as Bochs, VMware Workstation and PearPC, but has several features these lack, including increased speed on x86 (through an optional accelerator), and support for multiple architectures in-progress. By using dynamic translation it achieves a reasonable speed while being easy to port on new host CPUs.

Contents

[edit] Details

QEMU has two operating modes:

User mode emulation
QEMU can launch Linux or Darwin/Mac OS X processes compiled for one CPU on another CPU. Target OS system calls are thunked for endianness and 32/64 bit mismatches. Wine and DOSEMU are the main targets for QEMU.
Complete Computer System mode emulation
QEMU emulates a full computer system, including a processor and various peripherals. It can be used to provide virtual hosting of several virtual computers on a single computer.

The majority of the program is under the LGPL, with the user mode emulation under the GPL.

[edit] Accelerator

Fabrice Bellard also wrote a Linux kernel module (with preliminary ports to FreeBSD and Windows) named KQEMU or QEMU Accelerator, which notably speeds up i386 emulation on i386 platforms. This is accomplished by running user mode code directly on the host computer's CPU, and using processor and peripheral emulation only for kernel mode and real mode code. KQEMU also supports a kernel emulation mode in which portions of kernel mode code run on the host's CPU.

[edit] KQEMU versus QVM86

QEMU accelerator module was initially released as a closed-source proprietary product (although it was always given away at zero cost). Since version 1.3.0pre10[1][2], which was released on 2007-02-05, it has been available under the GNU General Public License.

When QEMU accelerator was still proprietary, a GPL-licensed module appeared that purported to perform the same task, QVM86, although it was abandoned as of early 2007 when VirtualBox was released.

KQEMU has been licensed by Win4Lin for use in their Win4Lin Pro Desktop product.

[edit] VirtualBox

In January 2007, VirtualBox was released, which has a built-in dynamic recompiler that is based on QEMU. As with KQEMU, it runs nearly all guest code natively on the host, and uses the recompiler only for special situations. In addition, VirtualBox goes through a lot of code analysis and patching via a built-in disassembler to reduce usage of the recompiler to a minimum. VirtualBox is open-source software under the GPL, except for a number of enterprise features.

[edit] Features

  • Supports emulating IA-32 (x86) PCs, AMD64 PCs, MIPS R4000, Sun's SPARC sun4m, Sun's SPARC sun4u, ARM development boards (Integrator/CP and Versatile/PB), SH4 SHIX board, and PowerPC (PReP and Power Macintosh) architectures.
  • Support for other architectures in both host and emulated systems (see homepage for complete list).
  • Increased speed — some applications can run in close to real time.
  • Implements Copy-On-Write disk image formats. You can declare a multi-gigabyte virtual drive, the disk image will only be as large as what is actually used.
  • Also implements overlay images. You can keep a snapshot of the guest system, and write changes to a separate image file. If the guest system breaks, it's simple to roll back to the snapshot.
  • Support for running Linux binaries for other architectures.
  • Can save and restore the state of the machine (programs running, etc.).
  • Virtual network card emulation.
  • SMP support.
  • Guest OS does not need to be modified/patched
  • Performance is improved when the KQEMU kernel module is used.
  • Command line tools allow a full control of QEMU without having to run X11.
  • Remote control of emulated machine via integrated VNC server
  • USB tablet support - this provides "grabless" mouse control. Activated with "-usb -usbdevice tablet".

[edit] Lacks

  • Incomplete support for Microsoft Windows and other host operating systems (emulation of these systems is just fine). This has improved with recent versions.
  • Incomplete support for less frequently-used architectures.
  • No special device drivers (graphics, sound, IO) for guests are available thus quite large overhead for multimedia applications.
    • A Cirrus Logic graphics chip and various popular sound cards (ES1370, Sound Blaster 16, and AdLib) are emulated, but they do not provide hardware-accelerated performance on the host system.
  • Supports only SDL or Cocoa video output libraries although a patch for GGI support exists[1]
  • Windows port includes the proprietary FMOD sound layer so it does not qualify as free open source software[2]

[edit] Example of QEMU's usage

This command will create a 500MB hard disk image in QEMU's "qcow" format

qemu-img create -f qcow c.img 500M

In this command the -f option is for the disk image format. The following formats are supported: vvfat, vpc, bochs, dmg, cloop, vmdk, cow, qcow, and raw, depending on the OS. See also: .img and .iso. The supported filesystem formats are abbreviations for:

  • vvfat - Virtual VFAT
  • vpc - Virtual PC
  • bochs - Bochs filesystem
  • dmg - macintosh Disk iMaGe
  • cloop - linux Compressed LOOP
  • vmdk - vmware Virtual Machine DisK format
  • qcow - QEMU Copy-On-Write
  • qcow2 - QEMU Copy-On-Write (new in version 0.9)
  • raw - RAW filesystem (no special format)
  • cow - user mode linux Copy-On-Write

The following command will start a virtual machine with 128MB of memory, using the c.img file created with the previous command and booting from a CD-ROM image linux.iso. The virtual machine will have audio support and use the system's clock to run in "real time." Note that one could also replace the -cdrom linux.iso parameter with -cdrom /dev/cdrom or whatever one's CD-ROM device is, and physically boot from installation medium and install to the image specified after -hda, in this case c.img.

qemu -hda c.img -cdrom linux.iso -boot d -m 128 -soundhw sb16 -localtime

This will create a virtual machine with 64MB of memory, booting from c.img and using the system's CD-ROM drive. The virtual machine will run in full-screen mode.

qemu -hda c.img -cdrom /dev/cdrom -boot c -m 64 -full-screen

While a virtual machine is running, press Ctrl-Alt-2 to access the "QEMU console", which lets one control the virtual machine (for example, changing disk images, rebooting, quitting QEMU, etc.) and Ctrl-Alt-1 to switch back to your emulation. Ctrl-Alt-F toggles between full-screen and windowed mode.

[edit] See also

Portal:Free software
 Free software Portal

[edit] References

  1. ^ http://members.aon.at/berny_f/qemu/
  2. ^ http://www.fmod.org/

[edit] External links

Retrieved from "http://en.wikipedia.org../../../q/e/m/QEMU_6cc3.html"