qemu-doc.texi

qemu性能直逼VMware的仿真器QEMU 的模擬速度約為實機的 25％；約為 Bochs 的 60 倍。Plex86、User-Mode-Linux、VMware 和 Virtual PC 則比

every disk image. The size of a snapshot in a disk image is difficult
to evaluate and is not shown by @code{info snapshots} because the
associated disk sectors are shared among all the snapshots to save
disk space (otherwise each snapshot would need a full copy of all the
disk images).

When using the (unrelated) @code{-snapshot} option
(@ref{disk_images_snapshot_mode}), you can always make VM snapshots,
but they are deleted as soon as you exit QEMU.

VM snapshots currently have the following known limitations:
@itemize
@item 
They cannot cope with removable devices if they are removed or
inserted after a snapshot is done.
@item 
A few device drivers still have incomplete snapshot support so their
state is not saved or restored properly (in particular USB).
@end itemize

@node qemu_img_invocation
@subsection @code{qemu-img} Invocation

@include qemu-img.texi

@node host_drives
@subsection Using host drives

In addition to disk image files, QEMU can directly access host
devices. We describe here the usage for QEMU version >= 0.8.3.

@subsubsection Linux

On Linux, you can directly use the host device filename instead of a
disk image filename provided you have enough proviledge to access
it. For example, use @file{/dev/cdrom} to access to the CDROM or
@file{/dev/fd0} for the floppy.

@table @code
@item CD
You can specify a CDROM device even if no CDROM is loaded. QEMU has
specific code to detect CDROM insertion or removal. CDROM ejection by
the guest OS is supported. Currently only data CDs are supported.
@item Floppy
You can specify a floppy device even if no floppy is loaded. Floppy
removal is currently not detected accurately (if you change floppy
without doing floppy access while the floppy is not loaded, the guest
OS will think that the same floppy is loaded).
@item Hard disks
Hard disks can be used. Normally you must specify the whole disk
(@file{/dev/hdb} instead of @file{/dev/hdb1}) so that the guest OS can
see it as a partitioned disk. WARNING: unless you know what you do, it
is better to only make READ-ONLY accesses to the hard disk otherwise
you may corrupt your host data (use the @option{-snapshot} command
line option or modify the device permissions accordingly).
@end table

@subsubsection Windows

@table @code
@item CD
The prefered syntax is the drive letter (e.g. @file{d:}). The
alternate syntax @file{\\.\d:} is supported. @file{/dev/cdrom} is
supported as an alias to the first CDROM drive.

Currently there is no specific code to handle removable medias, so it
is better to use the @code{change} or @code{eject} monitor commands to
change or eject media.
@item Hard disks
Hard disks can be used with the syntax: @file{\\.\PhysicalDriveN}
where @var{N} is the drive number (0 is the first hard disk).

WARNING: unless you know what you do, it is better to only make
READ-ONLY accesses to the hard disk otherwise you may corrupt your
host data (use the @option{-snapshot} command line so that the
modifications are written in a temporary file).
@end table


@subsubsection Mac OS X

@file{/dev/cdrom} is an alias to the first CDROM. 

Currently there is no specific code to handle removable medias, so it
is better to use the @code{change} or @code{eject} monitor commands to
change or eject media.

@node disk_images_fat_images
@subsection Virtual FAT disk images

QEMU can automatically create a virtual FAT disk image from a
directory tree. In order to use it, just type:

@example 
qemu linux.img -hdb fat:/my_directory
@end example

Then you access access to all the files in the @file{/my_directory}
directory without having to copy them in a disk image or to export
them via SAMBA or NFS. The default access is @emph{read-only}.

Floppies can be emulated with the @code{:floppy:} option:

@example 
qemu linux.img -fda fat:floppy:/my_directory
@end example

A read/write support is available for testing (beta stage) with the
@code{:rw:} option:

@example 
qemu linux.img -fda fat:floppy:rw:/my_directory
@end example

What you should @emph{never} do:
@itemize
@item use non-ASCII filenames ;
@item use "-snapshot" together with ":rw:" ;
@item expect it to work when loadvm'ing ;
@item write to the FAT directory on the host system while accessing it with the guest system.
@end itemize

@node pcsys_network
@section Network emulation

QEMU can simulate several networks cards (NE2000 boards on the PC
target) and can connect them to an arbitrary number of Virtual Local
Area Networks (VLANs). Host TAP devices can be connected to any QEMU
VLAN. VLAN can be connected between separate instances of QEMU to
simulate large networks. For simpler usage, a non priviledged user mode
network stack can replace the TAP device to have a basic network
connection.

@subsection VLANs

QEMU simulates several VLANs. A VLAN can be symbolised as a virtual
connection between several network devices. These devices can be for
example QEMU virtual Ethernet cards or virtual Host ethernet devices
(TAP devices).

@subsection Using TAP network interfaces

This is the standard way to connect QEMU to a real network. QEMU adds
a virtual network device on your host (called @code{tapN}), and you
can then configure it as if it was a real ethernet card.

@subsubsection Linux host

As an example, you can download the @file{linux-test-xxx.tar.gz}
archive and copy the script @file{qemu-ifup} in @file{/etc} and
configure properly @code{sudo} so that the command @code{ifconfig}
contained in @file{qemu-ifup} can be executed as root. You must verify
that your host kernel supports the TAP network interfaces: the
device @file{/dev/net/tun} must be present.

See @ref{sec_invocation} to have examples of command lines using the
TAP network interfaces.

@subsubsection Windows host

There is a virtual ethernet driver for Windows 2000/XP systems, called
TAP-Win32. But it is not included in standard QEMU for Windows,
so you will need to get it separately. It is part of OpenVPN package,
so download OpenVPN from : @url{http://openvpn.net/}.

@subsection Using the user mode network stack

By using the option @option{-net user} (default configuration if no
@option{-net} option is specified), QEMU uses a completely user mode
network stack (you don't need root priviledge to use the virtual
network). The virtual network configuration is the following:

@example

         QEMU VLAN      <------>  Firewall/DHCP server <-----> Internet
                           |          (10.0.2.2)
                           |
                           ---->  DNS server (10.0.2.3)
                           |     
                           ---->  SMB server (10.0.2.4)
@end example

The QEMU VM behaves as if it was behind a firewall which blocks all
incoming connections. You can use a DHCP client to automatically
configure the network in the QEMU VM. The DHCP server assign addresses
to the hosts starting from 10.0.2.15.

In order to check that the user mode network is working, you can ping
the address 10.0.2.2 and verify that you got an address in the range
10.0.2.x from the QEMU virtual DHCP server.

Note that @code{ping} is not supported reliably to the internet as it
would require root priviledges. It means you can only ping the local
router (10.0.2.2).

When using the built-in TFTP server, the router is also the TFTP
server.

When using the @option{-redir} option, TCP or UDP connections can be
redirected from the host to the guest. It allows for example to
redirect X11, telnet or SSH connections.

@subsection Connecting VLANs between QEMU instances

Using the @option{-net socket} option, it is possible to make VLANs
that span several QEMU instances. See @ref{sec_invocation} to have a
basic example.

@node direct_linux_boot
@section Direct Linux Boot

This section explains how to launch a Linux kernel inside QEMU without
having to make a full bootable image. It is very useful for fast Linux
kernel testing.

The syntax is:
@example
qemu -kernel arch/i386/boot/bzImage -hda root-2.4.20.img -append "root=/dev/hda"
@end example

Use @option{-kernel} to provide the Linux kernel image and
@option{-append} to give the kernel command line arguments. The
@option{-initrd} option can be used to provide an INITRD image.

When using the direct Linux boot, a disk image for the first hard disk
@file{hda} is required because its boot sector is used to launch the
Linux kernel.

If you do not need graphical output, you can disable it and redirect
the virtual serial port and the QEMU monitor to the console with the
@option{-nographic} option. The typical command line is:
@example
qemu -kernel arch/i386/boot/bzImage -hda root-2.4.20.img \
     -append "root=/dev/hda console=ttyS0" -nographic
@end example

Use @key{Ctrl-a c} to switch between the serial console and the
monitor (@pxref{pcsys_keys}).

@node pcsys_usb
@section USB emulation

QEMU emulates a PCI UHCI USB controller. You can virtually plug
virtual USB devices or real host USB devices (experimental, works only
on Linux hosts).  Qemu will automatically create and connect virtual USB hubs
as necessary to connect multiple USB devices.

@menu
* usb_devices::
* host_usb_devices::
@end menu
@node usb_devices
@subsection Connecting USB devices

USB devices can be connected with the @option{-usbdevice} commandline option
or the @code{usb_add} monitor command.  Available devices are:

@table @var
@item @code{mouse}
Virtual Mouse.  This will override the PS/2 mouse emulation when activated.
@item @code{tablet}
Pointer device that uses absolute coordinates (like a touchscreen).
This means qemu is able to report the mouse position without having
to grab the mouse.  Also overrides the PS/2 mouse emulation when activated.
@item @code{disk:file}
Mass storage device based on @var{file} (@pxref{disk_images})
@item @code{host:bus.addr}
Pass through the host device identified by @var{bus.addr}
(Linux only)
@item @code{host:vendor_id:product_id}
Pass through the host device identified by @var{vendor_id:product_id}
(Linux only)
@end table

@node host_usb_devices
@subsection Using host USB devices on a Linux host

WARNING: this is an experimental feature. QEMU will slow down when
using it. USB devices requiring real time streaming (i.e. USB Video
Cameras) are not supported yet.

@enumerate
@item If you use an early Linux 2.4 kernel, verify that no Linux driver 
is actually using the USB device. A simple way to do that is simply to
disable the corresponding kernel module by renaming it from @file{mydriver.o}
to @file{mydriver.o.disabled}.

@item Verify that @file{/proc/bus/usb} is working (most Linux distributions should enable it by default). You should see something like that:
@example
ls /proc/bus/usb
001  devices  drivers
@end example

@item Since only root can access to the USB devices directly, you can either launch QEMU as root or change the permissions of the USB devices you want to use. For testing, the following suffices:
@example
chown -R myuid /proc/bus/usb
@end example

@item Launch QEMU and do in the monitor:
@example 
info usbhost
  Device 1.2, speed 480 Mb/s
    Class 00: USB device 1234:5678, USB DISK
@end example
You should see the list of the devices you can use (Never try to use
hubs, it won't work).

@item Add the device in QEMU by using:
@example 
usb_add host:1234:5678
@end example

Normally the guest OS should report that a new USB device is
plugged. You can use the option @option{-usbdevice} to do the same.

@item Now you can try to use the host USB device in QEMU.

@end enumerate

When relaunching QEMU, you may have to unplug and plug again the USB
device to make it work again (this is a bug).

@node gdb_usage
@section GDB usage

QEMU has a primitive support to work with gdb, so that you can do
'Ctrl-C' while the virtual machine is running and inspect its state.

In order to use gdb, launch qemu with the '-s' option. It will wait for a
gdb connection:
@example
> qemu -s -kernel arch/i386/boot/bzImage -hda root-2.4.20.img \
       -append "root=/dev/hda"
Connected to host network interface: tun0
Waiting gdb connection on port 1234
@end example

Then launch gdb on the 'vmlinux' executable:
@example
> gdb vmlinux
@end example

In gdb, connect to QEMU:
@example
(gdb) target remote localhost:1234
@end example

Then you can use gdb normally. For example, type 'c' to launch the kernel:
@example
(gdb) c
@end example

Here are some useful tips in order to use gdb on system code:

@enumerate
@item
Use @code{info reg} to display all the CPU registers.
@item
Use @code{x/10i $eip} to display the code at the PC position.
@item
Use @code{set architecture i8086} to dump 16 bit code. Then use
@code{x/10i $cs*16+$eip} to dump the code at the PC position.
@end enumerate

@node pcsys_os_specific
@section Target OS specific information

@subsection Linux

To have access to SVGA graphic modes under X11, use the @code{vesa} or
the @code{cirrus} X11 driver. For optimal performances, use 16 bit
color depth in the guest and the host OS.

When using a 2.6 guest Linux kernel, you should add the option
@code{clock=pit} on the kernel command line because the 2.6 Linux
kernels make very strict real time clock checks by default that QEMU
cannot simulate exactly.

When using a 2.6 guest Linux kernel, verify that the 4G/4G patch is
not activated because QEMU is slower with this patch. The QEMU
Accelerator Module is also much slower in this case. Earlier Fedora
Core 3 Linux kernel (< 2.6.9-1.724_FC3) were known to incorporte this
patch by default. Newer kernels don't have it.

@subsection Windows

If you have a slow host, using Windows 95 is better as it gives the
best speed. Windows 2000 is also a good choice.

@subsubsection SVGA graphic modes support

QEMU emulates a Cirrus Logic GD5446 Video
card. All Windows versions starting from Windows 95 should recognize
and use this graphic card. For optimal performances, use 16 bit color
depth in the guest and the host OS.

If you are using Windows XP as guest OS and if you want to use high
resolution modes which the Cirrus Logic BIOS does not support (i.e. >=
1280x1024x16), then you should use the VESA VBE virtual graphic card
(option @option{-std-vga}).

@subsubsection CPU usage reduction

Windows 9x does not correctly use the CPU HLT
instruction. The result is that it takes host CPU cycles even when
idle. You can install the utility from
@url{http://www.user.cityline.ru/~maxamn/amnhltm.zip} to solve this
problem. Note that no such tool is needed for NT, 2000 or XP.

@subsubsection Windows 2000 disk full problem

Windows 2000 has a bug which gives a disk full problem during its
installation. When installing it, use the @option{-win2k-hack} QEMU
option to enable a specific workaround. After Windows 2000 is
installed, you no longer need this option (this option slows down the
IDE transfers).

@subsubsection Windows 2000 shutdown

Windows 2000 cannot automatically shutdown in QEMU although Windows 98
can. It comes from the fact that Windows 2000 does not automatically
use the APM driver provided by the BIOS.

In order to correct that, do the following (thanks to Struan
Bartlett): go to the Control Panel => Add/Remove Hardware & Next =>
Add/Troubleshoot a device => Add a new device & Next => No, select the
hardware from a list & Next => NT Apm/Legacy Support & Next => Next
(again) a few times. Now the driver is installed and Windows 2000 now
correctly instructs QEMU to shutdown at the appropriate moment. 

@subsubsection Share a directory between Unix and Windows

See @ref{sec_invocation} about the help of the option @option{-smb}.

@subsubsection Windows XP security problem

Some releases of Windows XP install correctly but give a security
error when booting:
@example
A problem is preventing Windows from accurately checking the
license for this computer. Error code: 0x800703e6.
@end example

The workaround is to install a service pack for XP after a boot in safe
mode. Then reboot, and the problem should go away. Since there is no
network while in safe mode, its recommended to download the full
installation of SP1 or SP2 and transfer that via an ISO or using the
vvfat block device ("-hdb fat:directory_which_holds_the_SP").

@subsection MS-DOS and FreeDOS

@subsubsection CPU usage reduction

DOS does not correctly use the CPU HLT instruction. The result is that
it takes host CPU cycles even when idle. You can install the utility
from @url{http://www.vmware.com/software/dosidle210.zip} to solve this
problem.

@node QEMU System emulator for non PC targets
@chapter QEMU System emulator for non PC targets

QEMU is a generic emulator and it emulates many non PC
machines. Most of the options are similar to the PC emulator. The
differences are mentionned in the following sections.

@menu
* QEMU PowerPC System emulator::
* Sparc32 System emulator invocation::
* Sparc64 System emulator invocation::
* MIPS System emulator invocation::
* ARM System emulator invocation::
@end menu

@node QEMU PowerPC System emulator
@section QEMU PowerPC System emulator

Use the executable @file{qemu-system-ppc} to simulate a complete PREP
or PowerMac PowerPC system.

QEMU emulates the following PowerMac peripherals:

@itemize @minus
@item 
UniNorth PCI Bridge 
@item
PCI VGA compatible card with VESA Bochs Extensions
@item 
2 PMAC IDE interfaces with hard disk and CD-ROM support
@item 
NE2000 PCI adapters
@item
Non Volatile RAM
@item
VIA-CUDA with ADB keyboard and mouse.
@end itemize

QEMU emulates the following PREP peripherals:

@itemize @minus
@item 
PCI Bridge
@item
PCI VGA compatible card with VESA Bochs Extensions
@item 
2 IDE interfaces with hard disk and CD-ROM support
@item
Floppy disk
@item 
NE2000 network adapters
@item
Serial port
@item
PREP Non Volatile RAM
@item
PC compatible keyboard and mouse.