1 ================================
2 Early creation of mapped devices
3 ================================
4
5 It is possible to configure a device-mapper de
6 your system in two ways.
7
8 The first is to build an initial ramdisk which
9 which configures the device, then pivot_root(8
10
11 The second is to create one or more device-map
12 "dm-mod.create=" through the kernel boot comma
13
14 The format is specified as a string of data se
15 semi-colons, where:
16
17 - a comma is used to separate fields like nam
18 (specifies one device)
19 - a semi-colon is used to separate devices.
20
21 So the format will look like this::
22
23 dm-mod.create=<name>,<uuid>,<minor>,<flags>,<
24
25 Where::
26
27 <name> ::= The device name.
28 <uuid> ::= xxxxxxxx-xxxx-xxxx
29 <minor> ::= The device minor n
30 <flags> ::= "ro" | "rw"
31 <table> ::= <start_sector> <nu
32 <target_type> ::= "verity" | "linear
33
34 The dm line should be equivalent to the one us
35 `--concise` argument.
36
37 Target types
38 ============
39
40 Not all target types are available as there ar
41 activation of certain DM targets without first
42 the validity of associated metadata.
43
44 ======================= ======================
45 `cache` constrained, userspace
46 `crypt` allowed
47 `delay` allowed
48 `era` constrained, userspace
49 `flakey` constrained, meant for
50 `linear` allowed
51 `log-writes` constrained, userspace
52 `mirror` constrained, userspace
53 `raid` constrained, userspace
54 `snapshot` constrained, userspace
55 `snapshot-origin` allowed
56 `snapshot-merge` constrained, userspace
57 `striped` allowed
58 `switch` constrained, userspace
59 `thin` constrained, requires
60 `thin-pool` constrained, requires
61 `verity` allowed
62 `writecache` constrained, userspace
63 `zero` constrained, not meant
64 ======================= ======================
65
66 If the target is not listed above, it is const
67
68 Examples
69 ========
70 An example of booting to a linear array made u
71 devices::
72
73 dm-mod.create="lroot,,,rw, 0 4096 linear 98:
74
75 This will boot to a rw dm-linear target of 819
76 devices identified by their major:minor number
77 this target to /dev/mapper/lroot (depending on
78
79 An example of multiple device-mappers, with th
80 is shown here split on multiple lines for read
81
82 dm-linear,,1,rw,
83 0 32768 linear 8:1 0,
84 32768 1024000 linear 8:2 0;
85 dm-verity,,3,ro,
86 0 1638400 verity 1 /dev/sdc1 /dev/sdc2 409
87 ac87db56303c9c1da433d7209b5a6ef3e4779df141
88 5ebfe87f7df3235b80a117ebc4078e44f55045487a
89
90 Other examples (per target):
91
92 "crypt"::
93
94 dm-crypt,,8,ro,
95 0 1048576 crypt aes-xts-plain64
96 babebabebabebabebabebabebabebabebabebabeba
97 /dev/sda 0 1 allow_discards
98
99 "delay"::
100
101 dm-delay,,4,ro,0 409600 delay /dev/sda1 0 50
102
103 "linear"::
104
105 dm-linear,,,rw,
106 0 32768 linear /dev/sda1 0,
107 32768 1024000 linear /dev/sda2 0,
108 1056768 204800 linear /dev/sda3 0,
109 1261568 512000 linear /dev/sda4 0
110
111 "snapshot-origin"::
112
113 dm-snap-orig,,4,ro,0 409600 snapshot-origin
114
115 "striped"::
116
117 dm-striped,,4,ro,0 1638400 striped 4 4096
118 /dev/sda1 0 /dev/sda2 0 /dev/sda3 0 /dev/sda
119
120 "verity"::
121
122 dm-verity,,4,ro,
123 0 1638400 verity 1 8:1 8:2 4096 4096 20480
124 fb1a5a0f00deb908d8b53cb270858975e76cf64105
125 51934789604d1b92399c52e7cb149d1b3a1b74bbbc
126
127 For setups using device-mapper on top of async
128 devices (MMC, USB, ..), it may be necessary to
129 explicitly wait for them to become available b
130 device-mapper tables. This can be done with th
131 module parameter, which takes a list of device
132
133 dm-mod.waitfor=<device1>[,..,<deviceN>]
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