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-rw-r--r--Documentation/device-mapper/dm-init.rst (renamed from Documentation/device-mapper/dm-init.txt)89
1 files changed, 50 insertions, 39 deletions
diff --git a/Documentation/device-mapper/dm-init.txt b/Documentation/device-mapper/dm-init.rst
index 8464ee7c01b8..e5242ff17e9b 100644
--- a/Documentation/device-mapper/dm-init.txt
+++ b/Documentation/device-mapper/dm-init.rst
@@ -1,5 +1,6 @@
+================================
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.
@@ -12,15 +13,17 @@ The second is to create one or more device-mappers using the module parameter
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:
+So the format will look like this::
dm-mod.create=<name>,<uuid>,<minor>,<flags>,<table>[,<table>+][;<name>,<uuid>,<minor>,<flags>,<table>[,<table>+]+]
-Where,
+Where::
+
<name> ::= The device name.
<uuid> ::= xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx | ""
<minor> ::= The device minor number | ""
@@ -29,7 +32,7 @@ Where,
<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.
+`--concise` argument.
Target types
============
@@ -38,32 +41,34 @@ 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
+======================= =======================================================
+`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:
+devices::
dm-mod.create="lroot,,,rw, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" root=/dev/dm-0
@@ -71,43 +76,49 @@ 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:
+An example of multiple device-mappers, with the dm-mod.create="..." contents
+is shown here split on multiple lines for readability::
- vroot,,,ro,
- 0 1740800 verity 254:0 254:0 1740800 sha1
- 76e9be054b15884a9fa85973e9cb274c93afadb6
- 5b3549d54d6c7a3837b9b81ed72e49463a64c03680c47835bef94d768e5646fe;
- vram,,,rw,
- 0 32768 linear 1:0 0,
- 32768 32768 linear 1:1 0
+ 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":
+"crypt"::
+
dm-crypt,,8,ro,
0 1048576 crypt aes-xts-plain64
babebabebabebabebabebabebabebabebabebabebabebabebabebabebabebabe 0
/dev/sda 0 1 allow_discards
-"delay":
+"delay"::
+
dm-delay,,4,ro,0 409600 delay /dev/sda1 0 500
-"linear":
+"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":
+"snapshot-origin"::
+
dm-snap-orig,,4,ro,0 409600 snapshot-origin 8:2
-"striped":
+"striped"::
+
dm-striped,,4,ro,0 1638400 striped 4 4096
/dev/sda1 0 /dev/sda2 0 /dev/sda3 0 /dev/sda4 0
-"verity":
+"verity"::
+
dm-verity,,4,ro,
0 1638400 verity 1 8:1 8:2 4096 4096 204800 1 sha256
fb1a5a0f00deb908d8b53cb270858975e76cf64105d412ce764225d53b8f3cfd