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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.
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...
