<s>
The	O
device	B-Application
mapper	I-Application
is	O
a	O
framework	B-Architecture
provided	O
by	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
for	O
mapping	O
physical	O
block	O
devices	O
onto	O
higher-level	O
virtual	B-Application
block	I-Application
devices	I-Application
.	O
</s>
<s>
It	O
forms	O
the	O
foundation	O
of	O
the	O
logical	B-Application
volume	I-Application
manager	I-Application
(	O
LVM	O
)	O
,	O
software	O
RAIDs	B-Architecture
and	O
dm-crypt	O
disk	O
encryption	O
,	O
and	O
offers	O
additional	O
features	O
such	O
as	O
file	O
system	O
snapshots	B-Application
.	O
</s>
<s>
Device	B-Application
mapper	I-Application
works	O
by	O
passing	O
data	O
from	O
a	O
virtual	B-Application
block	I-Application
device	I-Application
,	O
which	O
is	O
provided	O
by	O
the	O
device	B-Application
mapper	I-Application
itself	O
,	O
to	O
another	O
block	O
device	O
.	O
</s>
<s>
Data	O
can	O
be	O
also	O
modified	O
in	O
transition	O
,	O
which	O
is	O
performed	O
,	O
for	O
example	O
,	O
in	O
the	O
case	O
of	O
device	B-Application
mapper	I-Application
providing	O
disk	O
encryption	O
or	O
simulation	O
of	O
unreliable	O
hardware	O
behavior	O
.	O
</s>
<s>
This	O
article	O
focuses	O
on	O
the	O
device	B-Application
mapper	I-Application
implementation	O
in	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
but	O
the	O
device	B-Application
mapper	I-Application
functionality	O
is	O
also	O
available	O
in	O
both	O
NetBSD	B-Device
and	O
DragonFly	B-Application
BSD	I-Application
.	O
</s>
<s>
Applications	O
(	O
like	O
LVM2	B-Application
and	O
Enterprise	B-Application
Volume	I-Application
Management	I-Application
System	I-Application
(	O
EVMS	B-Application
)	O
)	O
that	O
need	O
to	O
create	O
new	O
mapped	O
devices	O
talk	O
to	O
the	O
device	B-Application
mapper	I-Application
via	O
the	O
libdevmapper.so	O
shared	B-Library
library	I-Library
,	O
which	O
in	O
turn	O
issues	O
ioctls	B-Operating_System
to	O
the	O
/dev/mapper/control	O
device	B-Application
node	I-Application
.	O
</s>
<s>
Configuration	O
of	O
the	O
device	B-Application
mapper	I-Application
can	O
be	O
also	O
examined	O
and	O
configured	O
interactivelyor	O
from	O
shell	O
scriptsby	O
using	O
the	O
utility	O
.	O
</s>
<s>
Both	O
of	O
these	O
two	O
userspace	O
components	O
have	O
their	O
source	O
code	O
maintained	O
alongside	O
the	O
LVM2	B-Application
source	O
.	O
</s>
<s>
Functions	O
provided	O
by	O
the	O
device	B-Application
mapper	I-Application
include	O
linear	O
,	O
striped	O
and	O
error	O
mappings	O
,	O
as	O
well	O
as	O
crypt	O
and	O
multipath	B-Application
targets	O
.	O
</s>
<s>
For	O
example	O
,	O
two	O
disks	O
may	O
be	O
concatenated	O
into	O
one	O
logical	B-Application
volume	I-Application
with	O
a	O
pair	O
of	O
linear	O
mappings	O
,	O
one	O
for	O
each	O
disk	O
.	O
</s>
<s>
As	O
another	O
example	O
,	O
crypt	O
target	O
encrypts	O
the	O
data	O
passing	O
through	O
the	O
specified	O
device	O
,	O
by	O
using	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
's	O
Crypto	B-Application
API	I-Application
.	O
</s>
<s>
Linux	B-Operating_System
kernel	I-Operating_System
features	O
and	O
projects	O
built	O
on	O
top	O
of	O
the	O
device	B-Application
mapper	I-Application
include	O
the	O
following	O
:	O
</s>
