<s>
A	O
virtual	B-Language
kernel	I-Language
architecture	O
(	O
vkernel	B-Language
)	O
is	O
an	O
operating	B-General_Concept
system	I-General_Concept
virtualisation	B-General_Concept
paradigm	O
where	O
kernel	O
code	O
can	O
be	O
compiled	O
to	O
run	O
in	O
the	O
user	B-Operating_System
space	I-Operating_System
,	O
for	O
example	O
,	O
to	O
ease	O
debugging	O
of	O
various	O
kernel-level	O
components	O
,	O
in	O
addition	O
to	O
general-purpose	O
virtualisation	B-General_Concept
and	O
compartmentalisation	O
of	O
system	B-General_Concept
resources	I-General_Concept
.	O
</s>
<s>
It	O
is	O
used	O
by	O
DragonFly	B-Application
BSD	I-Application
in	O
its	O
vkernel	B-Language
implementation	O
since	O
DragonFly	O
1.7	O
,	O
having	O
been	O
first	O
revealed	O
in	O
,	O
and	O
first	O
released	O
in	O
the	O
stable	O
branch	O
with	O
DragonFly	O
1.8	O
in	O
.	O
</s>
<s>
The	O
long-term	O
goal	O
,	O
in	O
addition	O
to	O
easing	O
kernel	O
development	O
,	O
is	O
to	O
make	O
it	O
easier	O
to	O
support	O
internet-connected	O
computer	B-Architecture
clusters	I-Architecture
without	O
compromising	O
local	O
security	O
.	O
</s>
<s>
Similar	O
concepts	O
exist	O
in	O
other	O
operating	B-General_Concept
systems	I-General_Concept
as	O
well	O
;	O
in	O
Linux	O
,	O
a	O
similar	O
virtualisation	B-General_Concept
concept	O
is	O
known	O
as	O
user-mode	B-Application
Linux	I-Application
;	O
whereas	O
in	O
NetBSD	B-Device
since	O
the	O
summer	O
of	O
2007	O
,	O
it	O
has	O
been	O
the	O
initial	O
focus	O
of	O
the	O
rump	B-Application
kernel	I-Application
infrastructure	O
.	O
</s>
<s>
The	O
virtual	B-Language
kernel	I-Language
concept	O
is	O
nearly	O
the	O
exact	O
opposite	O
of	O
the	O
unikernel	B-Operating_System
concept	O
—	O
with	O
vkernel	B-Language
,	O
kernel	O
components	O
get	O
to	O
run	O
in	O
userspace	B-Operating_System
to	O
ease	O
kernel	O
development	O
and	O
debugging	O
,	O
supported	O
by	O
a	O
regular	O
operating	B-General_Concept
system	I-General_Concept
kernel	O
;	O
whereas	O
with	O
a	O
unikernel	B-Operating_System
,	O
userspace-level	O
components	O
get	O
to	O
run	O
directly	O
in	O
kernel	B-Operating_System
space	I-Operating_System
for	O
extra	O
performance	O
,	O
supported	O
by	O
baremetal	O
hardware	O
or	O
a	O
hardware	O
virtualisation	B-General_Concept
stack	O
.	O
</s>
<s>
However	O
,	O
both	O
vkernels	B-Language
and	O
unikernels	B-Operating_System
can	O
be	O
used	O
for	O
similar	O
tasks	O
as	O
well	O
,	O
for	O
example	O
,	O
to	O
self-contain	O
software	O
to	O
a	O
virtualised	O
environment	O
with	O
low	O
overhead	O
.	O
</s>
<s>
In	O
fact	O
,	O
NetBSD	B-Device
's	O
rump	B-Application
kernel	I-Application
,	O
originally	O
having	O
a	O
focus	O
of	O
running	O
kernel	O
components	O
in	O
userspace	B-Operating_System
,	O
has	O
since	O
shifted	O
into	O
the	O
unikernel	B-Operating_System
space	O
as	O
well	O
(	O
going	O
after	O
the	O
anykernel	B-Application
moniker	O
for	O
supporting	O
both	O
paradigms	O
)	O
.	O
</s>
<s>
The	O
vkernel	B-Language
concept	O
is	O
different	O
from	O
a	O
FreeBSD	B-Language
jail	I-Language
in	O
that	O
a	O
jail	O
is	O
only	O
meant	O
for	O
resource	O
isolation	O
,	O
and	O
cannot	O
be	O
used	O
to	O
develop	O
and	O
test	O
new	O
kernel	O
functionality	O
in	O
the	O
userland	O
,	O
because	O
each	O
jail	O
is	O
sharing	O
the	O
same	O
kernel	O
.	O
</s>
<s>
(	O
DragonFly	O
,	O
however	O
,	O
still	O
has	O
FreeBSD	B-Language
jail	I-Language
support	O
as	O
well	O
.	O
)	O
</s>
<s>
In	O
DragonFly	O
,	O
the	O
vkernel	B-Language
can	O
be	O
thought	O
of	O
as	O
a	O
first-class	O
computer	B-General_Concept
architecture	I-General_Concept
,	O
comparable	O
to	O
i386	O
or	O
amd64	O
,	O
and	O
,	O
according	O
to	O
Matthew	O
Dillon	O
circa	O
2007	O
,	O
can	O
be	O
used	O
as	O
a	O
starting	O
point	O
for	O
porting	O
DragonFly	B-Application
BSD	I-Application
to	O
new	O
architectures	O
.	O
</s>
<s>
DragonFly	O
's	O
vkernel	B-Language
is	O
supported	O
by	O
the	O
host	O
kernel	O
through	O
new	O
system	B-Operating_System
calls	I-Operating_System
that	O
help	O
manage	O
virtual	O
memory	O
address	O
space	O
(	O
vmspace	O
)	O
—	O
vmspace_create( )	O
et	O
al.	O
,	O
as	O
well	O
as	O
extensions	O
to	O
several	O
existing	O
system	B-Operating_System
calls	I-Operating_System
like	O
mmap	B-Operating_System
's	O
madvise	O
—	O
mcontrol	O
.	O
</s>
