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New systemd services for startup:
lvm-devices-wait.service
Used in place of systemd-udev-settle, this service waits
for udev+pvscan to process PVs listed in system.devices.
It runs the command "lvmdevices --wait pvsonline".
This only waits for PVs that can be matched to a device in
sysfs, so it only waits for devices attached to the system.
It waits specifically for the /run/lvm/pvs_online/<pvid>
files to be created by pvscan. It quits waiting after a
configurable number of seconds. This service gives the
first activation service a chance to activate VGs from
PVs that are available immediately at startup. If this
service quits waiting before all the expected pvid files
appear, then the VG associated with those PVs will most
likely be activated by the -last service rather than the
initial -main service. If those PVs are even slower to
complete processing than the -last service, then the VG
will be activated by event activation whenever they are
finally complete.
lvm-activate-vgs-main.service
Calls "vgchange -aay", after lvm-devices-wait, to activate
complete VGs. It only considers PVs that have been
processed by udev+pvscan and have pvs_online files.
This is expected to activate VGs from basic devices
(not virtual device types) that are present at startup.
lvm-activate-vgs-last.service
Calls "vgchange -aay", after multipathd has started, to
activate VGs that became available after virtual device
services were started, e.g. VGs on multipath devices.
Like -main, it only looks at PVs that have been processed
by pvscan.
This vgchange in the -last service enables event activation
by creating the /run/lvm/event-activation-on file. Event
activation will activate any further VGs that appear on the
system (or complete udev processing) after the -last service.
In the case of event activation, the udev rule will run
vgchange -aay <vgname> via a transient service
lvm-activate-<vgname>.service. This vgchange only scans
PVs in the VG being activated, also based on the pvs_online
files from pvscan.
When there are many VGs that need activation during system
startup, the two fixed services can activate them all much
faster than activating each VG individually via events.
lvm.conf auto_activation_settings can be used to configure
the behavior (default ["service_and_event", "pvscan_hints"]).
"service_and_event" - the behavior described above, where
activation services are used first, and event activation
is used afterward.
"service_only" - only lvm-activate-vgs-* are used, and
no event-based activation occurs after the services finish.
(Equivalent to setting lvm.conf event_activation=0.)
"event_only" - the lvm-activate-vgs* services are skipped,
and all VGs are activated individually with event-based
activation.
"pvscan_hints" - the vgchange autoactivation commands
use pvs_online files created by pvscan. This optimization
limits the devices scanned by the vgchange command to only
PVs that have been processed by pvscan.
expands commit d5a06f9a7d
"pvscan: skip indexing devices used by LVs"
The dev cache index is expensive and slow, so limit it
to commands that are used to observe the state of lvm.
The index is only used to print warnings about incorrect
device use by active LVs, e.g. if an LV is using a
multipath component device instead of the multipath
device. Commands that continue to use the index and
print the warnings:
fullreport, lvmdiskscan, vgs, lvs, pvs,
vgdisplay, lvdisplay, pvdisplay,
vgscan, lvscan, pvscan (excluding --cache)
A couple other commands were borrowing the DEV_USED_FOR_LV
flag to just check if a device was actively in use by LVs.
These are converted to the new dev_is_used_by_active_lv().
dev_cache_index_devs() is taking a large amount of time
when there are many PVs. The index keeps track of
devices that are currently in use by active LVs. This
info is used to print warnings for users in some limited
cases.
The checks/warnings that are enabled by the index are not
needed by pvscan --cache, so disable it in this case.
This may be expanded to other cases in future commits.
dev_cache_index_devs should also be improved in another
commit to avoid the extreme delays with many devices.
When adding a device to the devices file with --adddev, lvm
by default chooses the best device ID type for the new device.
The new --deviceidtype option allows the user to override the
built in preference. This is useful if there's a problem with
the default type, or if a secondary type is preferrable.
If the specified deviceidtype does not produce a device ID,
then lvm falls back to the preference it would otherwise use.
error reading dev and no pvid on dev were both
returning 0. make it easier for callers to
know which, if they care.
return 1 if the device could be read, regardless
of whether a pvid was found or not.
set has_pvid=1 if a pvid is found and 0 if no
pvid is found.
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
