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lvm2/lib/label/label.h
David Teigland ef96186add device usage based on devices file 
The devices file /etc/lvm/devices/system.devices is a list of
devices that lvm can use.  This is the default system devices
file, which is specified in lvm.conf devices/devicesfile.

The command option --devicesfile <filename> allows lvm to be
used with a different set of devices.  This allows different
applications to use lvm on different sets of devices, e.g.
system devices do not need to be exposed to an application
using lvm on its own devices, and application devices do not
need to be exposed to the system.

In most cases (with limited exceptions), lvm will not read or
use a device not listed in the devices file.  When the devices
file is used, the regex filter is not used, and the filter
settings in lvm.conf are ignored.  filter-deviceid is used
when the devices file is enabled, and rejects any device that
does not match an entry in the devices file.

Set use_devicesfile=0 in lvm.conf or set --devicesfile ""
on the command line to disable the use of a devices file.
When disabled, lvm will see and use any device on the system
that passes the regex filter (and other standard filters.)

A device ID, e.g. wwid or serial number from sysfs, is a
unique ID that identifies a device.  The device ID is
generally independent of the device content, and lvm can
get the device ID without reading the device.
The device ID is used in the devices file as the primary
method of identifying device entries, and is also included
in VG metadata for PVs.

Each device_id has a device_id_type which indicates where
the device_id comes from, e.g. "sys_wwid" means the device_id
comes from the sysfs wwid file.  Others are sys_serial,
mpath_uuid, loop_file, md_uuid, devname.  (devname is the
device path, which is a fallback when no other proper
device_id_type is available.)

filter-deviceid permits lvm to use only devices on the system
that have a device_id matching a devices file entry.  Using
the device_id, lvm can determine the set of devices to use
without reading any devices, so the devices file will constrain
lvm in two ways:
1. it limits the devices that lvm will read.
2. it limits the devices that lvm will use.

In some uncommon cases, e.g. when devices have no unique ID
and device_id has to fall back to using the devname, lvm may
need to read all devices on the system to determine which
ones correspond to the devices file entries.  In this case,
the devices file does not limit the devices that lvm reads,
but it does limit the devices that lvm uses.

pvcreate/vgcreate/vgextend are not constrained by the devices
file, and will look outside it to find the new PV.  They assign
the new PV a device_id and add it to the devices file.  It is
also possible to explicitly add new PVs to the devices file before
using them in pvcreate/etc, in which case these commands would not
need to look outside the devices file for the new device.

vgimportdevices VG looks at all devices on the system to find an
existing VG and add its devices to the devices file.  The command
is not limited by an existing devices file.  The command will also
add device_ids to the VG metadata if the VG does not yet include
device_ids.  vgimportdevices -a imports devices for all accessible
VGs.  Since vgimportdevices does not limit itself to devices in
an existing devices file, the lvm.conf regex filter applies.
Adding --foreign will import devices for foreign VGs, but device_ids
are not added to foreign VGs.  Incomplete VGs are not imported.

The lvmdevices command manages the devices file.  The primary
purpose is to edit the devices file, but it will read PV headers
to find/check PVIDs.  (It does not read, process or modify VG
metadata.)

lvmdevices
. Displays devices file entries.
lvmdevices --check
. Checks devices file entries.
lvmdevices --update
. Updates devices file entries.
lvmdevices --adddev <devname>
. Adds devices_file entry (reads pv header).
lvmdevices --deldev <devname>
. Removes devices file entry.
lvmdevices --addpvid <pvid>
. Reads pv header of all devices to find <pvid>,
  and if found adds devices file entry.
lvmdevices --delpvid <pvid>
. Removes devices file entry.

The vgimportclone command has a new option --importdevices
that does the equivalent of vgimportdevices with the cloned
devices that are being imported.  The devices are "uncloned"
(new vgname and pvids) while at the same time adding the
devices to the devices file.  This allows cloned PVs to be
imported without duplicate PVs ever appearing on the system.

The command option --devices <devnames> allows a specific
list of devices to be exposed to the lvm command, overriding
the devices file.
2021-02-17 15:17:12 -06:00

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/*
* Copyright (C) 2002-2004 Sistina Software, Inc. All rights reserved.
* Copyright (C) 2004-2007 Red Hat, Inc. All rights reserved.
*
* This file is part of LVM2.
*
* This copyrighted material is made available to anyone wishing to use,
* modify, copy, or redistribute it subject to the terms and conditions
* of the GNU Lesser General Public License v.2.1.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef _LVM_LABEL_H
#define _LVM_LABEL_H
#include "lib/uuid/uuid.h"
#include "lib/device/device.h"
#include "lib/device/bcache.h"
#define LABEL_ID "LABELONE"
#define LABEL_SIZE SECTOR_SIZE /* Think very carefully before changing this */
#define LABEL_SCAN_SECTORS 4L
#define LABEL_SCAN_SIZE (LABEL_SCAN_SECTORS << SECTOR_SHIFT)
struct labeller;
struct dev_filter;
struct cmd_context;
struct logical_volume;
/* On disk - 32 bytes */
struct label_header {
int8_t id[8]; /* LABELONE */
uint64_t sector_xl; /* Sector number of this label */
uint32_t crc_xl; /* From next field to end of sector */
uint32_t offset_xl; /* Offset from start of struct to contents */
int8_t type[8]; /* LVM2 001 */
} __attribute__ ((packed));
/* In core */
struct label {
char type[8];
uint64_t sector;
struct labeller *labeller;
struct device *dev;
void *info;
};
struct labeller;
struct label_ops {
/*
* Is the device labelled with this format ?
*/
int (*can_handle) (struct labeller * l, void *buf, uint64_t sector);
/*
* Write a label to a volume.
*/
int (*write) (struct label * label, void *buf);
/*
* Read a label from a volume.
*/
int (*read) (struct cmd_context *cmd, struct labeller * l, struct device * dev,
void *label_buf, uint64_t label_sector, int *is_duplicate);
/*
* Populate label_type etc.
*/
int (*initialise_label) (struct labeller * l, struct label * label);
/*
* Destroy a previously read label.
*/
void (*destroy_label) (struct labeller * l, struct label * label);
/*
* Destructor.
*/
void (*destroy) (struct labeller * l);
};
struct labeller {
struct label_ops *ops;
const struct format_type *fmt;
};
int label_init(void);
void label_exit(void);
int label_register_handler(struct labeller *handler);
struct labeller *label_get_handler(const char *name);
int label_remove(struct device *dev);
int label_write(struct device *dev, struct label *label);
struct label *label_create(struct labeller *labeller);
void label_destroy(struct label *label);
extern struct bcache *scan_bcache;
int label_scan(struct cmd_context *cmd);
int label_scan_devs(struct cmd_context *cmd, struct dev_filter *f, struct dm_list *devs);
int label_scan_devs_cached(struct cmd_context *cmd, struct dev_filter *f, struct dm_list *devs);
int label_scan_devs_rw(struct cmd_context *cmd, struct dev_filter *f, struct dm_list *devs);
int label_scan_devs_excl(struct cmd_context *cmd, struct dev_filter *f, struct dm_list *devs);
int label_scan_dev(struct device *dev);
void label_scan_invalidate(struct device *dev);
void label_scan_invalidate_lv(struct cmd_context *cmd, struct logical_volume *lv);
void label_scan_drop(struct cmd_context *cmd);
void label_scan_destroy(struct cmd_context *cmd);
int label_scan_setup_bcache(void);
int label_scan_open(struct device *dev);
int label_scan_open_excl(struct device *dev);
int label_scan_open_rw(struct device *dev);
int label_scan_reopen_rw(struct device *dev);
int label_read_pvid(struct device *dev);
int label_scan_for_pvid(struct cmd_context *cmd, char *pvid, struct device **dev_out);
/*
* Wrappers around bcache equivalents.
* (these make it easier to disable bcache and revert to direct rw if needed)
*/
bool dev_read_bytes(struct device *dev, uint64_t start, size_t len, void *data);
bool dev_write_bytes(struct device *dev, uint64_t start, size_t len, void *data);
bool dev_write_zeros(struct device *dev, uint64_t start, size_t len);
bool dev_set_bytes(struct device *dev, uint64_t start, size_t len, uint8_t val);
bool dev_invalidate_bytes(struct device *dev, uint64_t start, size_t len);
void dev_set_last_byte(struct device *dev, uint64_t offset);
void dev_unset_last_byte(struct device *dev);
#endif
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