docs: device-mapper: move it to the admin-guide

[linux-2.6-microblaze.git] / Documentation / device-mapper / dm-init.rst

diff --git a/Documentation/device-mapper/dm-init.rst b/Documentation/device-mapper/dm-init.rst
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-================================
-Early creation of mapped devices
-================================
-
-It is possible to configure a device-mapper device to act as the root device for
-your system in two ways.
-
-The first is to build an initial ramdisk which boots to a minimal userspace
-which configures the device, then pivot_root(8) in to it.
-
-The second is to create one or more device-mappers using the module parameter
-"dm-mod.create=" through the kernel boot command line argument.
-
-The format is specified as a string of data separated by commas and optionally
-semi-colons, where:
-
- - a comma is used to separate fields like name, uuid, flags and table
-   (specifies one device)
- - a semi-colon is used to separate devices.
-
-So the format will look like this::
-
- dm-mod.create=<name>,<uuid>,<minor>,<flags>,<table>[,<table>+][;<name>,<uuid>,<minor>,<flags>,<table>[,<table>+]+]
-
-Where::
-
-       <name>          ::= The device name.
-       <uuid>          ::= xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx | ""
-       <minor>         ::= The device minor number | ""
-       <flags>         ::= "ro" | "rw"
-       <table>         ::= <start_sector> <num_sectors> <target_type> <target_args>
-       <target_type>   ::= "verity" | "linear" | ... (see list below)
-
-The dm line should be equivalent to the one used by the dmsetup tool with the
-`--concise` argument.
-
-Target types
-============
-
-Not all target types are available as there are serious risks in allowing
-activation of certain DM targets without first using userspace tools to check
-the validity of associated metadata.
-
-======================= =======================================================
-`cache`                        constrained, userspace should verify cache device
-`crypt`                        allowed
-`delay`                        allowed
-`era`                  constrained, userspace should verify metadata device
-`flakey`               constrained, meant for test
-`linear`               allowed
-`log-writes`           constrained, userspace should verify metadata device
-`mirror`               constrained, userspace should verify main/mirror device
-`raid`                 constrained, userspace should verify metadata device
-`snapshot`             constrained, userspace should verify src/dst device
-`snapshot-origin`      allowed
-`snapshot-merge`       constrained, userspace should verify src/dst device
-`striped`              allowed
-`switch`               constrained, userspace should verify dev path
-`thin`                 constrained, requires dm target message from userspace
-`thin-pool`            constrained, requires dm target message from userspace
-`verity`               allowed
-`writecache`           constrained, userspace should verify cache device
-`zero`                 constrained, not meant for rootfs
-======================= =======================================================
-
-If the target is not listed above, it is constrained by default (not tested).
-
-Examples
-========
-An example of booting to a linear array made up of user-mode linux block
-devices::
-
-  dm-mod.create="lroot,,,rw, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" root=/dev/dm-0
-
-This will boot to a rw dm-linear target of 8192 sectors split across two block
-devices identified by their major:minor numbers.  After boot, udev will rename
-this target to /dev/mapper/lroot (depending on the rules). No uuid was assigned.
-
-An example of multiple device-mappers, with the dm-mod.create="..." contents
-is shown here split on multiple lines for readability::
-
-  dm-linear,,1,rw,
-    0 32768 linear 8:1 0,
-    32768 1024000 linear 8:2 0;
-  dm-verity,,3,ro,
-    0 1638400 verity 1 /dev/sdc1 /dev/sdc2 4096 4096 204800 1 sha256
-    ac87db56303c9c1da433d7209b5a6ef3e4779df141200cbd7c157dcb8dd89c42
-    5ebfe87f7df3235b80a117ebc4078e44f55045487ad4a96581d1adb564615b51
-
-Other examples (per target):
-
-"crypt"::
-
-  dm-crypt,,8,ro,
-    0 1048576 crypt aes-xts-plain64
-    babebabebabebabebabebabebabebabebabebabebabebabebabebabebabebabe 0
-    /dev/sda 0 1 allow_discards
-
-"delay"::
-
-  dm-delay,,4,ro,0 409600 delay /dev/sda1 0 500
-
-"linear"::
-
-  dm-linear,,,rw,
-    0 32768 linear /dev/sda1 0,
-    32768 1024000 linear /dev/sda2 0,
-    1056768 204800 linear /dev/sda3 0,
-    1261568 512000 linear /dev/sda4 0
-
-"snapshot-origin"::
-
-  dm-snap-orig,,4,ro,0 409600 snapshot-origin 8:2
-
-"striped"::
-
-  dm-striped,,4,ro,0 1638400 striped 4 4096
-  /dev/sda1 0 /dev/sda2 0 /dev/sda3 0 /dev/sda4 0
-
-"verity"::
-
-  dm-verity,,4,ro,
-    0 1638400 verity 1 8:1 8:2 4096 4096 204800 1 sha256
-    fb1a5a0f00deb908d8b53cb270858975e76cf64105d412ce764225d53b8f3cfd
-    51934789604d1b92399c52e7cb149d1b3a1b74bbbcb103b2a0aaacbed5c08584