Index: Documentation/device-mapper/boot.txt |
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+Boot time 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. |
+ |
+For simple device mapper configurations, it is possible to boot directly |
+using the following kernel command line: |
+ |
+dm="<name> <uuid> <ro>,table line 1,...,table line n" |
+ |
+name = the name to associate with the device |
+ after boot, udev, if used, will use that name to label |
+ the device node. |
+uuid = may be 'none' or the UUID desired for the device. |
+ro = may be "ro" or "rw". If "ro", the device and device table will be |
+ marked read-only. |
+ |
+Each table line may be as normal when using the dmsetup tool except for |
+two variations: |
+1. Any use of commas will be interpreted as a newline |
+2. Quotation marks cannot be escaped and cannot be used without |
+ terminating the dm= argument. |
+ |
+Unless renamed by udev, the device node created will be dm-0 as the |
+first minor number for the device-mapper is used during early creation. |
+ |
+Example |
+======= |
+ |
+- Booting to a linear array made up of user-mode linux block devices: |
+ |
+ dm="lroot none 0, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" \ |
+ root=/dev/dm-0 |
+ |
+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. |