| Will Drewry | ee3ad54 | 2010-06-09 17:47:38 -0500 | [diff] [blame] | 1 | Boot time creation of mapped devices |
| 2 | =================================== |
| 3 | |
| 4 | It is possible to configure a device mapper device to act as the root |
| 5 | device for your system in two ways. |
| 6 | |
| 7 | The first is to build an initial ramdisk which boots to a minimal |
| 8 | userspace which configures the device, then pivot_root(8) in to it. |
| 9 | |
| 10 | For simple device mapper configurations, it is possible to boot directly |
| 11 | using the following kernel command line: |
| 12 | |
| 13 | dm="<name> <uuid> <ro>,table line 1,...,table line n" |
| 14 | |
| 15 | name = the name to associate with the device |
| 16 | after boot, udev, if used, will use that name to label |
| 17 | the device node. |
| 18 | uuid = may be 'none' or the UUID desired for the device. |
| 19 | ro = may be "ro" or "rw". If "ro", the device and device table will be |
| 20 | marked read-only. |
| 21 | |
| 22 | Each table line may be as normal when using the dmsetup tool except for |
| 23 | two variations: |
| 24 | 1. Any use of commas will be interpreted as a newline |
| 25 | 2. Quotation marks cannot be escaped and cannot be used without |
| 26 | terminating the dm= argument. |
| 27 | |
| 28 | Unless renamed by udev, the device node created will be dm-0 as the |
| 29 | first minor number for the device-mapper is used during early creation. |
| 30 | |
| 31 | Example |
| 32 | ======= |
| 33 | |
| 34 | - Booting to a linear array made up of user-mode linux block devices: |
| 35 | |
| 36 | dm="lroot none 0, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" \ |
| 37 | root=/dev/dm-0 |
| 38 | |
| 39 | Will boot to a rw dm-linear target of 8192 sectors split across two |
| 40 | block devices identified by their major:minor numbers. After boot, udev |
| 41 | will rename this target to /dev/mapper/lroot (depending on the rules). |
| 42 | No uuid was assigned. |