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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
Internal detection of SCSI device being in-use by DM mpath has been
performed several times for each component device - this could be
eventually racy - so instead when we do remember 1st. checked result
for device being mpath and use it consistenly over the filter runtime.
Save the list of PVs in /run/lvm/hints. These hints
are used to reduce scanning in a number of commands
to only the PVs on the system, or only the PVs in a
requested VG (rather than all devices on the system.)
commit de28637
scan: use full md filter when md 1.0 devices are present
missed the fact that md superblock version 0.90 also puts
metadata at the end of the device, so the full md filter
needs to be used when either 0.90 or 1.0 is present.
devices/scan_lvs (default 1) determines whether lvm
will scan LVs for layered PVs. The lvm behavior has
always been to scan LVs, but it's rare for LVs to have
layered PVs, and much more common for there to be many
LVs that substantially slow down scanning with no benefit.
This is implemented in the usable filter, and has the
same effect as listing all LVs in the global_filter.
The md filter can operate in two native modes:
- normal: reads only the start of each device
- full: reads both the start and end of each device
md 1.0 devices place the superblock at the end of the device,
so components of this version will only be identified and
excluded when lvm uses the full md filter.
Previously, the full md filter was only used in commands
that could write to the device. Now, the full md filter
is also applied when there is an md 1.0 device present
on the system. This means the 'pvs' command can avoid
displaying md 1.0 components (at the cost of doubling
the i/o to every device on the system.)
(The md filter can operate in a third mode, using udev,
but this is disabled by default because there have been
problems with reliability of the info returned from udev.)
As we start refactoring the code to break dependencies (see doc/refactoring.txt),
I want us to use full paths in the includes (eg, #include "base/data-struct/list.h").
This makes it more obvious when we're breaking abstraction boundaries, eg, including a file in
metadata/ from base/
Filters are still applied before any device reading or
the label scan, but any filter checks that want to read
the device are skipped and the device is flagged.
After bcache is populated, but before lvm looks for
devices (i.e. before label scan), the filters are
reapplied to the devices that were flagged above.
The filters will then find the data they need in
bcache.
- Use 'lvmcache' consistently instead of 'metadata cache'
- Always use 5 characters for source line number
- Remember to convert uuids into printable form
- Use <no name> rather than (null) when VG has no name.
If we're using persistent .cache file, we're reading this file instead
of traversing the /dev content. Fix missing indexing by VGID and LVID
here - hook this into persistent_filter_load where we populate device
cache from persistent .cache file instead of scanning /dev.
For example, inducing situation in which we warn about different device
actually used than what LVM thinks should be used based on metadata:
$ lsblk -s /dev/vg/lvol0
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vg-lvol0 253:4 0 124M 0 lvm
`-loop1 7:1 0 128M 0 loop
$ lvmconfig --type diff
global {
use_lvmetad=0
}
devices {
obtain_device_list_from_udev=0
}
(obtain_device_list_from_udev=0 also means the persistent .cache file is used)
Before this patch - pvs is fine as it does the dev scan, but lvs relies
on persistent .cache file and it misses the VGID/LVID indices to check
and warn about incorrect devices used:
$ pvs
Found duplicate PV B9gXTHkIdEIiMVwcOoT2LX3Ywh4YIHgR: using /dev/loop0 not /dev/loop1
Using duplicate PV /dev/loop0 without holders, ignoring /dev/loop1
WARNING: Device mismatch detected for vg/lvol0 which is accessing /dev/loop1 instead of /dev/loop0.
PV VG Fmt Attr PSize PFree
/dev/loop0 vg lvm2 a-- 124.00m 0
$ lvs
Found duplicate PV B9gXTHkIdEIiMVwcOoT2LX3Ywh4YIHgR: using /dev/loop0 not /dev/loop1
Using duplicate PV /dev/loop0 without holders, ignoring /dev/loop1
LV VG Attr LSize
lvol0 vg -wi-a----- 124.00m
With this patch applied - both pvs and lvs is fine - the indices are
always created correctly (lvs just an example here, other LVM commands
that rely on persistent .cache file are fixed with this patch too):
$ pvs
Found duplicate PV B9gXTHkIdEIiMVwcOoT2LX3Ywh4YIHgR: using /dev/loop0 not /dev/loop1
Using duplicate PV /dev/loop0 without holders, ignoring /dev/loop1
WARNING: Device mismatch detected for vg/lvol0 which is accessing /dev/loop1 instead of /dev/loop0.
PV VG Fmt Attr PSize PFree
/dev/loop0 vg lvm2 a-- 124.00m 0
$ lvs
Found duplicate PV B9gXTHkIdEIiMVwcOoT2LX3Ywh4YIHgR: using /dev/loop0 not /dev/loop1
Using duplicate PV /dev/loop0 without holders, ignoring /dev/loop1
WARNING: Device mismatch detected for vg/lvol0 which is accessing /dev/loop1 instead of /dev/loop0.
LV VG Attr LSize
lvol0 vg -wi-a----- 124.00m
We already do check for suspended devs within udev rules where
the pvscan is to update lvmetad. So the check for suspended devs
in "pre-lvmetad" chain is not useful here - remove it - it may
be a source of hardly to detect races anyway (if udev rule detects
the device is not suspended and then the pvscan instance sees the
dev as suspended, we may end up not reacting to the event properly).
Fix regression introduced with commit:
2fc126b00d
This commit has moved pv_min_size() test in front
of device_is_usable(). However pv_min_size needs to open device,
so it may have actually get blocked.
So restore the original order and first validate
dm device to be usable for open.
It's worth to note that such check is not 'race-free',
but it usually eliminates 99.99% of problems ;).
Print [source:handler] in filters' debug messages only if external
device info source other than "none" is used.
$ lvmconfig --type full devices/external_device_info_source
external_device_info_source="none
Before this patch (from the -vvvv log):
filters/filter-usable.c:47 /dev/mapper/test: Skipping: Too small to hold a PV [none:(nil)]
filters/filter-md.c:33 /dev/sdb: Skipping md component device [none:(nil)]
filters/filter-partitioned.c:25 /dev/vda: Skipping: Partition table signature found [none:(nil)]
With this patch applied:
filters/filter-usable.c:44 /dev/mapper/test: Skipping: Too small to hold a PV
filters/filter-md.c:35 /dev/sdb: Skipping md component device
filters/filter-partitioned.c:27 /dev/vda: Skipping: Partition table signature found
Just like MD filtering that detects components of software RAID (md),
add detection for firmware RAID.
We're not adding any native code to detect this - there are lots of
firmware RAIDs out there which is just out of LVM scope. However,
with current changes with which we're able to get device info from
external sources (e.g. external_device_info_source="udev"), we can
do this easily if the external device status source has this kind
of information - which is the case of "udev" source where the results
of blkid scans are stored.
This detection should cover all firmware RAIDs that blkid can detect and
which are identified as:
ID_FS_TYPE = {adaptec,ddf,hpt45x,hpt37x,isw,jmicron,lsi_mega,nvidia,promise_fasttrack,silicon_medley,via}_raid_member
Partitioned devices are marked in udev db as:
ID_PART_TABLE="<partition table type name>"
and at the same time they are *not* marked with:
ID_PART_ENTRY_DISK="<parent disk major:minor>"
Where partition table type name is dos/gpt/... But checking the presence
of this variable is enough for LVM here - it just needs to know whether
there's a partition table or not, not interested in the actual type.
The same applies for parent disk major:minor.
The filter-partitioned code should contain only checks in "partition" domain.
The check for pv_min_size should actually be a part of filter-usable.
If the device size is less than pv_min_size, such device is not usable
as a PV so this check clearly belongs here logically.
With udev external info source, we can get device size via libudev's
sysfs reading interface and we can avoid opening the device this way
effectively.
mpath components are marked in udev db as:
ID_FS_TYPE="mpath_member"
or
DM_MULTIPATH_DEVICE_PATH="1"
(it depends on udev rule/blkid version used for handling mpath)
Composite filter is a filter that can put several filters in one set.
This patch adds a switch when creating the composite filter which will
enable or disable external device info handles for all the filters
the composite filter encompasses.
We want to use this external device info for majority of the filters
which are in the "lvmetad filter chain" (or the respective part if
we're not using lvmetad).
Following patches will use the enabled external device handle in
concrete filters from the composite filter...
