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Commit 0cc78aab authored by Will Drewry's avatar Will Drewry Committed by Amit Pundir
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CHROMIUM: dm: boot time specification of dm= 

This is a wrap-up of three patches pending upstream approval.
I'm bundling them because they are interdependent, and it'll be
easier to drop it on rebase later.

1. dm: allow a dm-fs-style device to be shared via dm-ioctl

Integrates feedback from Alisdair, Mike, and Kiyoshi.

Two main changes occur here:

- One function is added which allows for a programmatically created
mapped device to be inserted into the dm-ioctl hash table.  This binds
the device to a name and, optional, uuid which is needed by udev and
allows for userspace management of the mapped device.

- dm_table_complete() was extended to handle all of the final
functional changes required for the table to be operational once
called.

2. init: boot to device-mapper targets without an initr*

Add a dm= kernel parameter modeled after the md= parameter from
do_mounts_md.  It allows for device-mapper targets to be configured at
boot time for use early in the boot process (as the root device or
otherwise).  It also replaces /dev/XXX calls with major:minor opportunistically.

The format is dm="name uuid ro,table line 1,table line 2,...".  The
parser expects the comma to be safe to use as a newline substitute but,
otherwise, uses the normal separator of space.  Some attempt has been
made to make it forgiving of additional spaces (using skip_spaces()).

A mapped device created during boot will be assigned a minor of 0 and
may be access via /dev/dm-0.

An example dm-linear root with no uuid may look like:

root=/dev/dm-0  dm="lroot none ro, 0 4096 linear /dev/ubdb 0, 4096 4096 linear /dv/ubdc 0"

Once udev is started, /dev/dm-0 will become /dev/mapper/lroot.

Older upstream threads:
http://marc.info/?l=dm-devel&m=127429492521964&w=2
http://marc.info/?l=dm-devel&m=127429499422096&w=2
http://marc.info/?l=dm-devel&m=127429493922000&w=2

Latest upstream threads:
https://patchwork.kernel.org/patch/104859/
https://patchwork.kernel.org/patch/104860/
https://patchwork.kernel.org/patch/104861/



Bug: 27175947

Signed-off-by: default avatarWill Drewry <wad@chromium.org>

Review URL: http://codereview.chromium.org/2020011



Change-Id: I92bd53432a11241228d2e5ac89a3b20d19b05a31

[AmitP: Refactored the original changes based on upstream changes,
        commit e52347bd ("Documentation/admin-guide: split the kernel parameter list to a separate file")]
Signed-off-by: default avatarAmit Pundir <amit.pundir@linaro.org>
parent 68408632

Documentation/admin-guide/kernel-parameters.txt

+3 −0
Original line number Diff line number Diff line
@@ -837,6 +837,9 @@ 


	dis_ucode_ldr	[X86] Disable the microcode loader.



	dm=		[DM] Allows early creation of a device-mapper device.

			See Documentation/device-mapper/boot.txt.



	dma_debug=off	If the kernel is compiled with DMA_API_DEBUG support,

			this option disables the debugging code at boot.

Documentation/device-mapper/boot.txt

0 → 100644
+42 −0
Original line number Diff line number Diff line 
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.

drivers/md/dm-ioctl.c

+39 −0
Original line number Diff line number Diff line
@@ -1992,6 +1992,45 @@ void dm_interface_exit(void) 
	dm_hash_exit();

}





/**

 * dm_ioctl_export - Permanently export a mapped device via the ioctl interface

 * @md: Pointer to mapped_device

 * @name: Buffer (size DM_NAME_LEN) for name

 * @uuid: Buffer (size DM_UUID_LEN) for uuid or NULL if not desired

 */

int dm_ioctl_export(struct mapped_device *md, const char *name,

		    const char *uuid)

{

	int r = 0;

	struct hash_cell *hc;



	if (!md) {

		r = -ENXIO;

		goto out;

	}



	/* The name and uuid can only be set once. */

	mutex_lock(&dm_hash_cells_mutex);

	hc = dm_get_mdptr(md);

	mutex_unlock(&dm_hash_cells_mutex);

	if (hc) {

		DMERR("%s: already exported", dm_device_name(md));

		r = -ENXIO;

		goto out;

	}



	r = dm_hash_insert(name, uuid, md);

	if (r) {

		DMERR("%s: could not bind to '%s'", dm_device_name(md), name);

		goto out;

	}



	/* Let udev know we've changed. */

	dm_kobject_uevent(md, KOBJ_CHANGE, dm_get_event_nr(md));

out:

	return r;

}

/**

 * dm_copy_name_and_uuid - Copy mapped device name & uuid into supplied buffers

 * @md: Pointer to mapped_device

drivers/md/dm-table.c

+1 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <linux/vmalloc.h>

#include <linux/blkdev.h>

#include <linux/namei.h>

#include <linux/mount.h>

#include <linux/ctype.h>

#include <linux/string.h>

#include <linux/slab.h>

include/linux/device-mapper.h

+6 −0
Original line number Diff line number Diff line
@@ -430,6 +430,12 @@ void dm_put(struct mapped_device *md); 
void dm_set_mdptr(struct mapped_device *md, void *ptr);

void *dm_get_mdptr(struct mapped_device *md);



/*

 * Export the device via the ioctl interface (uses mdptr).

 */

int dm_ioctl_export(struct mapped_device *md, const char *name,

		    const char *uuid);



/*

 * A device can still be used while suspended, but I/O is deferred.

 */