GEOM_MAP(4) FreeBSD Kernel Interfaces Manual GEOM_MAP(4)
NAME
geom_map - GEOM module that maps defined items as separate partitions
SYNOPSIS
To compile this driver into the kernel, place the following line in your
kernel configuration file:
options geom_map
DESCRIPTION
The geom_map framework provides support for mapping defined parts of the
media. Basically it is helpful for embedded devices where in the one
continuous flash are loader, kernel and rootfs parts. geom_map allows
making them available as separate parts and protects the loader from
being overwritten.
At boot time geom_map partitions are listed (only with bootverbose) as:
MAP: 0x30000, data=0x30000 "/dev/map/bootloader"
MAP: 30000x10000, data=0x10000 "/dev/map/factory"
MAP: 40000x7a0000, data=0x7a0000 "/dev/map/upgrade"
MAP: search key ".!/bin/sh" from 0x100000, step 0x10000
MAP: 40000x110000, data=0x110000 "/dev/map/kernel"
MAP: search key ".!/bin/sh" from 0x100000, step 0x10000
MAP: 150000x690000, data=0x690000 "/dev/map/rootfs"
MAP: 7e0000x20000, data=0x20000 "/dev/map/config"
The current geom_map configuration can be accessed with the following
sysctl(8) nodes: kern.geom.conftxt, kern.geom.confxml, and
kern.geom.confdot or by using "geom map list".
# sysctl -n kern.geom.conftxt
0 MD md0 10485760 512 u 0 s 512 f 0 fs 0 l 10485760 t malloc
0 DISK cfid0 8388608 4 hd 0 sc 0
1 MAP map/config 131072 4 i 5 o 8257536 entry 0 dsize 131072
1 MAP map/rootfs 6881280 4 i 4 o 1376256 entry 0 dsize 6881280
2 UZIP map/rootfs.uzip 18677760 512
1 MAP map/kernel 1114112 4 i 3 o 262144 entry 0 dsize 1114112
1 MAP map/upgrade 7995392 4 i 2 o 262144 entry 0 dsize 7995392
1 MAP map/factory 65536 4 i 1 o 196608 entry 0 dsize 65536
1 MAP map/bootloader 196608 4 i 0 o 0 entry 0 dsize 196608
Driver configuration can be done in device.hints(5). List of used
parameters:
at select media to attach
name name of partition (will create device /dev/map/that_name)
start offset from the beginning of the parent media to start of the
mapped partition. This field can also have a special value
"search:searchstart:searchstep:searchkey", where:
searchstart
offset from the beginning of the parent media where
search will be started
searchstep
value of the increment used while searching for the
partition boundary markers
searchkey
key which will be used to find partition boundary
markers. The wildcard `.' can be used to match any
character on that position
end offset from the beginning of the parent media to the end of the
mapped partition. This field can also have the special value
"search:searchstart:searchstep:searchkey", as described above.
offset offset where the data of the mapped partition begins
Each record contains the start address (in bytes) from the media begin,
size (in bytes), offset where the data of mapped partition begins, and
the name of new device.
MAP: 150000x690000, data=0x690000 "/dev/map/rootfs"
00150000 - start address
00690000 - size
00000000 - data begin from zero offset
00690000 - data size
"map/rootfs" - new media will be accessible via /dev/map/rootfs dev.
EXAMPLES
If we need to implement layout shown above, we need to define the
following hints:
hint.map.0.at="cfid0"
hint.map.0.start=0x00000000
hint.map.0.end=0x00030000
hint.map.0.name="bootloader"
hint.map.0.readonly=1
This defines /dev/map/bootloader at disk cfid0 starting at 0x00000000 and
ending at 0x00030000, it is also marked as readonly.
hint.map.1.at="cfid0"
hint.map.1.start=0x00030000
hint.map.1.end=0x00040000
hint.map.1.name="factory"
hint.map.2.at="cfid0"
hint.map.2.start=0x00040000
hint.map.2.end=0x007e0000
hint.map.2.name="upgrade"
hint.map.3.at="cfid0"
hint.map.3.name="kernel"
hint.map.3.start=0x00040000
hint.map.3.end="search:0x00100000:0x10000:.!/bin/sh"
This defines /dev/map/kernel at disk cfid0 starting at 0x00040000, but
the end position must be searched by finding the key ".!/bin/sh", from
offset 0x00100000 to the end of media with step 0x10000. The real marker
in this case is "#!/bin/sh", but `#' terminates the line when the hints
file is parsed, so we need to use wildcard `.' instead of `#'.
hint.map.4.at="cfid0"
hint.map.4.name="rootfs"
hint.map.4.start="search:0x00100000:0x10000:.!/bin/sh"
hint.map.4.end=0x007e0000
hint.map.5.at="cfid0"
hint.map.5.start=0x007e0000
hint.map.5.end=0x00800000
hint.map.5.name="config"
SEE ALSO
geom(4), geom(8), sysctl(8)
AUTHORS
The geom_map driver was written by Aleksandr Rybalko <ray@ddteam.net>.
FreeBSD 13.1-RELEASE-p6 June 8, 2015 FreeBSD 13.1-RELEASE-p6
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