[RFC,v2,2/2] init: boot to device-mapper targets without an initr*

Commit Message

Will Drewry May 17, 2010, 6:13 p.m. UTC

None

Patch

diff --git a/Documentation/device-mapper/boot.txt
b/Documentation/device-mapper/boot.txt
new file mode 100644
index 0000000..00fb557
--- /dev/null
+++ b/Documentation/device-mapper/boot.txt
@@ -0,0 +1,36 @@ 
+Boot time creation of mapped devices
+===================================
+
+You can boot directly to a dm device using the following kernel command
+line:
+
+dm="<name> <uuid> <ro>,table line 1,...,table line n"
+
+name = the name to associated 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 0 or 1.  If non-zero, 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.
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index 839b21b..9e22f8e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -43,6 +43,7 @@  parameter is applicable:
 	AVR32	AVR32 architecture is enabled.
 	AX25	Appropriate AX.25 support is enabled.
 	BLACKFIN Blackfin architecture is enabled.
+	DM	Device mapper support is enabled.
 	DRM	Direct Rendering Management support is enabled.
 	EDD	BIOS Enhanced Disk Drive Services (EDD) is enabled
 	EFI	EFI Partitioning (GPT) is enabled
@@ -654,6 +655,9 @@  and is between 256 and 4096 characters. It is
defined in the file
 			Disable PIN 1 of APIC timer
 			Can be useful to work around chipset bugs.

+	dm=		[DM] Allows early creation of a device-mapper device.
+			See Documentation/device-mapper/boot.txt.
+
 	dmasound=	[HW,OSS] Sound subsystem buffers