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lvm2/lib/label/label.h
David Teigland 83fe6e720f device usage based on devices file 
The LVM devices file lists devices that lvm can use.  The default
file is /etc/lvm/devices/system.devices, and the lvmdevices(8)
command is used to add or remove device entries.  If the file
does not exist, or if lvm.conf includes use_devicesfile=0, then
lvm will not use a devices file.  When the devices file is in use,
the regex filter is not used, and the filter settings in lvm.conf
or on the command line are ignored.

LVM records devices in the devices file using hardware-specific
IDs, such as the WWID, and attempts to use subsystem-specific
IDs for virtual device types.  These device IDs are also written
in the VG metadata.  When no hardware or virtual ID is available,
lvm falls back using the unstable device name as the device ID.
When devnames are used, lvm performs extra scanning to find
devices if their devname changes, e.g. after reboot.

When proper device IDs are used, an lvm command will not look
at devices outside the devices file, but when devnames are used
as a fallback, lvm will scan devices outside the devices file
to locate PVs on renamed devices.  A config setting
search_for_devnames can be used to control the scanning for
renamed devname entries.

Related to the devices file, the new command option
--devices <devnames> allows a list of devices to be specified for
the command to use, overriding the devices file.  The listed
devices act as a sort of devices file in terms of limiting which
devices lvm will see and use.  Devices that are not listed will
appear to be missing to the lvm command.

Multiple devices files can be kept in /etc/lvm/devices, which
allows lvm to be used with different sets of devices, e.g.
system devices do not need to be exposed to a specific application,
and the application can use lvm on its own set of devices that are
not exposed to the system.  The option --devicesfile <filename> is
used to select the devices file to use with the command.  Without
the option set, the default system devices file is used.

Setting --devicesfile "" causes lvm to not use a devices file.

An existing, empty devices file means lvm will see no devices.

The new command vgimportdevices adds PVs from a VG to the devices
file and updates the VG metadata to include the device IDs.
vgimportdevices -a will import all VGs into the system devices file.

LVM commands run by dmeventd not use a devices file by default,
and will look at all devices on the system.  A devices file can
be created for dmeventd (/etc/lvm/devices/dmeventd.devices)  If
this file exists, lvm commands run by dmeventd will use it.

Internal implementaion:

- device_ids_read - read the devices file
  . add struct dev_use (du) to cmd->use_devices for each devices file entry
- dev_cache_scan - get /dev entries
  . add struct device (dev) to dev_cache for each device on the system
- device_ids_match - match devices file entries to /dev entries
  . match each du on cmd->use_devices to a dev in dev_cache, using device ID
  . on match, set du->dev, dev->id, dev->flags MATCHED_USE_ID
- label_scan - read lvm headers and metadata from devices
  . filters are applied, those that do not need data from the device
  . filter-deviceid skips devs without MATCHED_USE_ID, i.e.
    skips /dev entries that are not listed in the devices file
  . read lvm label from dev
  . filters are applied, those that use data from the device
  . read lvm metadata from dev
  . add info/vginfo structs for PVs/VGs (info is "lvmcache")
- device_ids_find_renamed_devs - handle devices with unstable devname ID
  where devname changed
  . this step only needed when devs do not have proper device IDs,
    and their dev names change, e.g. after reboot sdb becomes sdc.
  . detect incorrect match because PVID in the devices file entry
    does not match the PVID found when the device was read above
  . undo incorrect match between du and dev above
  . search system devices for new location of PVID
  . update devices file with new devnames for PVIDs on renamed devices
  . label_scan the renamed devs
- continue with command processing
2021-02-23 16:43:32 -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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