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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
dm-integrity stores checksums of the data written to an
LV, and returns an error if data read from the LV does
not match the previously saved checksum. When used on
raid images, dm-raid will correct the error by reading
the block from another image, and the device user sees
no error. The integrity metadata (checksums) are stored
on an internal LV allocated by lvm for each linear image.
The internal LV is allocated on the same PV as the image.
Create a raid LV with an integrity layer over each
raid image (for raid levels 1,4,5,6,10):
lvcreate --type raidN --raidintegrity y [options]
Add an integrity layer to images of an existing raid LV:
lvconvert --raidintegrity y LV
Remove the integrity layer from images of a raid LV:
lvconvert --raidintegrity n LV
Settings
Use --raidintegritymode journal|bitmap (journal is default)
to configure the method used by dm-integrity to ensure
crash consistency.
Initialization
When integrity is added to an LV, the kernel needs to
initialize the integrity metadata/checksums for all blocks
in the LV. The data corruption checking performed by
dm-integrity will only operate on areas of the LV that
are already initialized. The progress of integrity
initialization is reported by the "syncpercent" LV
reporting field (and under the Cpy%Sync lvs column.)
Example: create a raid1 LV with integrity:
$ lvcreate --type raid1 -m1 --raidintegrity y -n rr -L1G foo
Creating integrity metadata LV rr_rimage_0_imeta with size 12.00 MiB.
Logical volume "rr_rimage_0_imeta" created.
Creating integrity metadata LV rr_rimage_1_imeta with size 12.00 MiB.
Logical volume "rr_rimage_1_imeta" created.
Logical volume "rr" created.
$ lvs -a foo
LV VG Attr LSize Origin Cpy%Sync
rr foo rwi-a-r--- 1.00g 4.93
[rr_rimage_0] foo gwi-aor--- 1.00g [rr_rimage_0_iorig] 41.02
[rr_rimage_0_imeta] foo ewi-ao---- 12.00m
[rr_rimage_0_iorig] foo -wi-ao---- 1.00g
[rr_rimage_1] foo gwi-aor--- 1.00g [rr_rimage_1_iorig] 39.45
[rr_rimage_1_imeta] foo ewi-ao---- 12.00m
[rr_rimage_1_iorig] foo -wi-ao---- 1.00g
[rr_rmeta_0] foo ewi-aor--- 4.00m
[rr_rmeta_1] foo ewi-aor--- 4.00m
If udev info is missing for a device, (which would indicate
if it's an MD component), then do an end-of-device read to
check if a PV is an MD component. (This is skipped when
using hints since we already know devs in hints are good.)
A new config setting md_component_checks can be used to
disable the additional end-of-device MD checks, or to
always enable end-of-device MD checks.
When both hints and udev info are disabled/unavailable,
the end of PVs will now be scanned by default. If md
devices with end-of-device superblocks are not being
used, the extra I/O overhead can be avoided by setting
md_component_checks="start".
udev_dev_is_md_component and udev_dev_is_mpath_component
are not used for obtaining the device list, but they still
use libudev for device info. When there are problems with
udev, these functions can get stuck. So, use the existing
obtain_device_list_from_udev config setting to also control
whether these "is component" functions are used, which gives
us a way to avoid using libudev entirely when it's causing
problems.
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.)
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.
Rename dev_read() to dev_read_buf() - the function that reads data
into a supplied buffer.
Introduce a new dev_read() that allocates the buffer it returns and
switch the important users over to this. No caller may change the
returned data. (For now, callers are responsible for freeing it after
use, but later the device layer will take full ownership.)
dev_read_buf() should only be used for tiny buffers or unimportant code
(such as the old disk formats).
Introduce enum dev_io_reason to categorise block device I/O
in debug messages so it's obvious what it is for.
DEV_IO_SIGNATURES /* Scanning device signatures */
DEV_IO_LABEL /* LVM PV disk label */
DEV_IO_MDA_HEADER /* Text format metadata area header */
DEV_IO_MDA_CONTENT /* Text format metadata area content */
DEV_IO_FMT1 /* Original LVM1 metadata format */
DEV_IO_POOL /* Pool metadata format */
DEV_IO_LV /* Content written to an LV */
DEV_IO_LOG /* Logging messages */
Older udev versions (udev < v165), don't have the official
udev_device_get_is_initialized function available to query for
device initialization state in udev database. Also, devices don't
have USEC_INITIALIZED udev db variable set - this is bound to the
udev_device_get_is_initialized fn functionality.
In this case, check for "DEVLINKS" variable instead - all block devices
have at least one symlink set for the node (the "/dev/block/<major:minor>".
This symlink is set by default basic udev rules provided by udev directly.
We'll use this as an alternative for the check that initial udev
processing for a device has already finished.
Treat loop device created with 'losetup -P' as regular
partitioned device - so if it has partition table,
prevent its usage in commands like 'pvcreate'.
Before 'pvcreate /dev/loop0' could have erased and formated as PV,
after this patch, device is filtered out and cannot be used.
Recent kernel (4.4) start to report values smaller then sector size
(but in reporting size for SSD which support data zeroing on discard).
For now log warning and assume it really means 1 sector.
Addressing RHBZ:
https://bugzilla.redhat.com/show_bug.cgi?id=1313377
Non-dm devices have ID_PART_TABLE_TYPE variable exported in
udev db from blkid scan for *both* whole devices and partitions.
We used ID_PART_ENTRY_DISK in addition to decide whether this
is the whole device or partition and then we filtered out only
whole devices where the partition table really is.
However, ID_PART_ENTRY_DISK was added in blkid 2.20 so we need
to use a different set of variables to decide on whole devices
and partitions on systems where older blkid is still used.
Now, we use ID_PART_TABLE_TYPE to detect that there's something
related to partitioning with this device and we use DEVTYPE variable
instead to decide between whole device (DEVTYPE="disk") and partition
(DEVTYPE="partition").
For dm devices it's simpler, we have ID_PART_TABLE_TYPE variable\
set in udev db for whole devices. It's not set for partitions,
hence we don't need more variable in addition to make the decision
on whole device vs. partition (dm devices do not have regular
partitions, hence DEVTYPE can't be used anyway, it's always set
to "disk" for whole disks and partitions).
Doing 'stat' checking first and later opening is racy.
And since we do not really care about any 'status' info
here and we read 'sysfs' here - just drop whole 'stat()'
call and directly handle error from failing 'fopen()'.
The former patch(dab3ebce4c) is a little bit strict. For example, it is
OK to create PV on unpartitioned DASD devices with LDL formatted. So
after lvm version containing the patch, LVs created on those devices
could not be found.
Signed-off-by: Lidong Zhong <lzhong@suse.com>
Some signatures are spread around the disk in several copies, mainly for
backup. Make libblkid to detect these extra copies - there was missing
"blkid_probe_step_back" fn call after successful wipe of previous signature
copy.
An example with FAT table which has copies:
$ mkfs.vfat /dev/sda1
Before this patch:
$ pvcreate /dev/sda1
WARNING: vfat signature detected on /dev/sda1 at offset 54. Wipe it? [y/n]: y
Wiping vfat signature on /dev/sda1.
Physical volume "/dev/sda1" successfully created
With this patch applied:
$ pvcreate /dev/sda1
WARNING: vfat signature detected on /dev/sda1 at offset 54. Wipe it? [y/n]: y
Wiping vfat signature on /dev/sda1.
WARNING: vfat signature detected on /dev/sda1 at offset 0. Wipe it? [y/n]: y
Wiping vfat signature on /dev/sda1.
WARNING: vfat signature detected on /dev/sda1 at offset 510. Wipe it? [y/n]: y
Wiping vfat signature on /dev/sda1.
Physical volume "/dev/sda1" successfully created
