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.Dd March 28, 2010
.Dt VKERNEL 7
.Os
.Sh NAME
.Nm vkernel ,
.Nm vcd ,
.Nm vkd ,
.Nm vke
.Nd virtual kernel architecture
.Sh SYNOPSIS
.Cd "platform vkernel   # for 32 bit vkernels"
.Cd "platform vkernel64 # for 64 bit vkernels"
.Cd "device vcd"
.Cd "device vkd"
.Cd "device vke"
.Pp
.Pa /var/vkernel/boot/kernel
.Op Fl sUv
.Op Fl c Ar file
.Op Fl e Ar name Ns = Ns Li value : Ns Ar name Ns = Ns Li value : Ns ...
.Op Fl i Ar file
.Op Fl I Ar interface Ns Op Ar :address1 Ns Oo Ar :address2 Oc Ns Oo Ar /netmask Oc
.Op Fl l Ar cpulock
.Op Fl m Ar size
.Op Fl n Ar numcpus
.Op Fl p Ar file
.Op Fl r Ar file
.Sh DESCRIPTION
The
.Nm
architecture allows for running
.Dx
kernels in userland.
.Pp
The following options are available:
.Bl -tag -width ".Fl m Ar size"
.It Fl c Ar file
Specify a readonly CD-ROM image
.Ar file
to be used by the kernel, with the first
.Fl c
option defining
.Li vcd0 ,
the second one
.Li vcd1 ,
and so on.
The first
.Fl r
or
.Fl c
option specified on the command line will be the boot disk.
The CD9660 filesystem is assumed when booting from this media.
.It Fl e Ar name Ns = Ns Li value : Ns Ar name Ns = Ns Li value : Ns ...
Specify an environment to be used by the kernel.
.It Fl i Ar file
Specify a memory image
.Ar file
to be used by the virtual kernel.
If no
.Fl i
option is given, the kernel will generate a name of the form
.Pa /var/vkernel/memimg.XXXXXX ,
with the trailing
.Ql X Ns s
being replaced by a sequential number, e.g.\&
.Pa memimg.000001 .
.It Fl I Ar interface Ns Op Ar :address1 Ns Oo Ar :address2 Oc Ns Oo Ar /netmask Oc
Create a virtual network device, with the first
.Fl I
option defining
.Li vke0 ,
the second one
.Li vke1 ,
and so on.
.Pp
The
.Ar interface
argument is the name of a
.Xr tap 4
device node.
The
.Pa /dev/
path prefix does not have to be specified and will be automatically prepended.
Specifying
.Cm auto
will pick the first unused
.Xr tap 4
device.
.Pp
The
.Ar address1
and
.Ar address2
arguments are the IP addresses of the
.Xr tap 4
and
.Nm vke
interfaces.
Optionally,
.Ar address1
may be of the form
.Li bridge Ns Em X
in which case the
.Xr tap 4
interface is added to the specified
.Xr bridge 4
interface.
The
.Nm vke
address is not assigned until the interface is brought up in the guest.
.Pp
The
.Ar netmask
argument applies to all interfaces for which an address is specified.
.It Fl l Ar cpulock
Specify which, if any, real CPUs to lock virtual CPUs to.
.Ar cpulock
is one of
.Cm any ,
.Cm map Ns Op Ns , Ns Ar startCPU ,
or
.Ar CPU .
.Pp
.Cm any
does not map virtual CPUs to real CPUs.
This is the default.
.Pp
.Cm map Ns Op Ns , Ns Ar startCPU
maps each virtual CPU to a real CPU starting with real CPU 0 or
.Ar startCPU
if specified.
.Pp
.Ar CPU
locks all virtual CPUs to the real CPU specified by
.Ar CPU .
.It Fl m Ar size
Specify the amount of memory to be used by the kernel in bytes,
.Cm K
.Pq kilobytes ,
.Cm M
.Pq megabytes
or
.Cm G
.Pq gigabytes .
Lowercase versions of
.Cm K , M ,
and
.Cm G
are allowed.
.It Fl n Ar numcpus
Specify the number of CPUs you wish to emulate.
Up to 16 CPUs are supported.
The virtual kernel must be built with
.Cd options SMP
to use this option and will default to 2 CPUs unless otherwise specified.
.It Fl p Ar file
Specify a file in which to store the process ID.
A warning is issued if this file cannot be opened for writing.
.It Fl r Ar file
Specify a R/W disk image
.Ar file
to be used by the kernel, with the first
.Fl r
option defining
.Li vkd0 ,
the second one
.Li vkd1 ,
and so on.
The first
.Fl r
or
.Fl c
option specified on the command line will be the boot disk.
.It Fl s
Boot into single-user mode.
.It Fl U
Enable writing to kernel memory and module loading.
By default, those are disabled for security reasons.
.It Fl v
Turn on verbose booting.
.El
.Sh DEVICES
A number of virtual device drivers exist to supplement the virtual kernel.
.Ss Disk device
The
.Nm vkd
driver allows for up to 16
.Xr vn 4
based disk devices.
The root device will be
.Li vkd0
(see
.Sx EXAMPLES
for further information on how to prepare a root image).
.Ss CD-ROM device
The
.Nm vcd
driver allows for up to 16 virtual CD-ROM devices.
Basically this is a read only
.Nm vkd
device with a block size of 2048.
.Ss Network interface
The
.Nm vke
driver supports up to 16 virtual network interfaces which are associated with
.Xr tap 4
devices on the host.
For each
.Nm vke
device, the per-interface read only
.Xr sysctl 3
variable
.Va hw.vke Ns Em X Ns Va .tap_unit
holds the unit number of the associated
.Xr tap 4
device.
.Sh SIGNALS
The virtual kernel only enables
.Dv SIGQUIT
and
.Dv SIGTERM
while operating in regular console mode.
Sending
.Ql \&^\e
.Pq Dv SIGQUIT
to the virtual kernel causes the virtual kernel to enter its internal
.Xr ddb 4
debugger and re-enable all other terminal signals.
Sending
.Dv SIGTERM
to the virtual kernel triggers a clean shutdown by passing a
.Dv SIGUSR2
to the virtual kernel's
.Xr init 8
process.
.Sh DEBUGGING
It is possible to directly gdb the virtual kernel's process.
It is recommended that you do a
.Ql handle SIGSEGV noprint
to ignore page faults processed by the virtual kernel itself and
.Ql handle SIGUSR1 noprint
to ignore signals used for simulating inter-processor interrupts (SMP build
only).
.Sh FILES
.Bl -tag -width ".It Pa /sys/config/VKERNEL" -compact
.It Pa /sys/config/VKERNEL
default
.Nm
configuration file, for
.Xr config 8 .
.El
.Sh EXAMPLES
A couple of steps are necessary in order to prepare the system to build and
run a virtual kernel.
.Ss Setting up the filesystem
The
.Nm
architecture needs a number of files which reside in
.Pa /var/vkernel .
Since these files tend to get rather big and the
.Pa /var
partition is usually of limited size, we recommend the directory to be
created in the
.Pa /home
partition with a link to it in
.Pa /var :
.Bd -literal
mkdir -p /home/var.vkernel/boot
ln -s /home/var.vkernel /var/vkernel
.Ed
.Pp
Next, a filesystem image to be used by the virtual kernel has to be
created and populated (assuming world has been built previously).
If the image is created on a UFS filesystem you might want to pre-zero it.
On a HAMMER filesystem you should just truncate-extend to the image size
as HAMMER does not re-use data blocks already present in the file.
.Bd -literal
vnconfig -c -s labels -S 2g -T vn0 /var/vkernel/rootimg.01
disklabel -r -w vn0s0 auto
disklabel -e vn0s0	# add `a' partition with fstype `4.2BSD'
newfs /dev/vn0s0a
mount /dev/vn0s0a /mnt
cd /usr/src
make installworld DESTDIR=/mnt
cd etc
make distribution DESTDIR=/mnt
echo '/dev/vkd0s0a	/	ufs	rw	1  1' >/mnt/etc/fstab
echo 'proc		/proc	procfs	rw	0  0' >>/mnt/etc/fstab
.Ed
.Pp
Edit
.Pa /mnt/etc/ttys
and replace the
.Li console
entry with the following line and turn off all other gettys.
.Bd -literal
console	"/usr/libexec/getty Pc"		cons25	on  secure
.Ed
.Pp
Replace
.Li \&Pc
with
.Li al.Pc
if you would like to automatically log in as root.
.Pp
Then, unmount the disk.
.Bd -literal
umount /mnt
vnconfig -u vn0
.Ed
.Ss Compiling the virtual kernel
In order to compile a virtual kernel use the
.Li VKERNEL
kernel configuration file residing in
.Pa /sys/config
(or a configuration file derived thereof):
.Bd -literal
cd /usr/src
make -DNO_MODULES buildkernel KERNCONF=VKERNEL
make -DNO_MODULES installkernel KERNCONF=VKERNEL DESTDIR=/var/vkernel
.Ed
.Ss Enabling virtual kernel operation
A special
.Xr sysctl 8 ,
.Va vm.vkernel_enable ,
must be set to enable
.Nm
operation:
.Bd -literal
sysctl vm.vkernel_enable=1
.Ed
.Ss Configuring the network on the host system
In order to access a network interface of the host system from the
.Nm ,
you must add the interface to a
.Xr bridge 4
device which will then be passed to the
.Fl I
option:
.Bd -literal
kldload if_bridge.ko
kldload if_tap.ko
ifconfig bridge0 create
ifconfig bridge0 addm re0	# assuming re0 is the host's interface
ifconfig bridge0 up
.Ed
.Ss Running the kernel
Finally, the virtual kernel can be run:
.Bd -literal
cd /var/vkernel
\&./boot/kernel -m 64m -r rootimg.01 -I auto:bridge0
.Ed
.Pp
You can issue the
.Xr reboot 8 ,
.Xr halt 8 ,
or
.Xr shutdown 8
commands from inside a virtual kernel.
After doing a clean shutdown the
.Xr reboot 8
command will re-exec the virtual kernel binary while the other two will
cause the virtual kernel to exit.
.Sh BUILDING THE WORLD UNDER A VKERNEL
The virtual kernel platform does not have all the header files expected
by a world build, so the easiest thing to do right now is to specify a
pc32 (in a 32 bit vkernel) or pc64 (in a 64 bit vkernel) target when
building the world under a virtual kernel, like this:
.Bd -literal
vkernel# make MACHINE_PLATFORM=pc32 buildworld
vkernel# make MACHINE_PLATFORM=pc32 installworld
.Ed
.Sh CONFIGURATION FILES
Your virtual kernel is a complete
.Dx
system, but you might not want to run all the services a normal kernel runs.
Here is what a typical virtual kernel's
.Pa /etc/rc.conf
file looks like, with some additional possibilities commented out.
.Bd -literal
hostname="vkernel"
network_interfaces="lo0 vke0"
ifconfig_vke0="DHCP"
sendmail_enable="NO"
#syslog_enable="NO"
blanktime="NO"
.Ed
.Sh SEE ALSO
.Xr vknet 1 ,
.Xr bridge 4 ,
.Xr tap 4 ,
.Xr vn 4 ,
.Xr sysctl.conf 5 ,
.Xr build 7 ,
.Xr disklabel 8 ,
.Xr ifconfig 8 ,
.Xr vknetd 8 ,
.Xr vnconfig 8
.Rs
.%A Aggelos Economopoulos
.%D March 2007
.%T "A Peek at the DragonFly Virtual Kernel"
.Re
.Sh HISTORY
Virtual kernels were introduced in
.Dx 1.7 .
.Sh AUTHORS
.An -nosplit
.An Matt Dillon
thought up and implemented the
.Nm
architecture and wrote the
.Nm vkd
device driver.
.An Sepherosa Ziehau
wrote the
.Nm vke
device driver.
This manual page was written by
.An Sascha Wildner .