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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.
The args for pvcreate/pvremove (and vgcreate/vgextend
when applicable) were not efficiently opened, scanned,
and filtered. This change reorganizes the opening
and filtering in the following steps:
- label scan and filter all devs
. open ro
. standard label scan at the start of command
- label scan and filter dev args
. open ro
. uses full md component check
. typically the first scan and filter of pvcreate devs
- close and reopen dev args
. open rw and excl
- repeat label scan and filter dev args
. using reopened rw excl fd
- wipe and write new headers
. using reopened rw excl fd
To read the lvm headers and set dev->pvid if the
device is a PV. Difference from label_scan_ functions
is this does not read any vg metadata or add any info
to lvmcache.
lvm opens devices readonly to scan them, but
needs to open then readwrite to update the metadata.
Previously, the ro fd was closed before the rw fd
was opened, leaving a small gap where the dev was
not held open, and during which the dev could
possibly change which storage it referred to.
With the bcache_change_fd() interface, lvm opens a
rw fd on a device to be written, tells bcache to
change to the new rw fd, and closes the ro fd.
. open dev ro
. read dev with the ro fd (label_scan)
. lock vg (ex for writing)
. open dev rw
. close ro fd
. rescan dev to check if the metadata changed
between the scan and the lock
. if the metadata did change, reread in full
. write the metadata
When vg_read rescans devices with the intention of
writing the VG, the label rescan can open the devs
RW so they do not need to be closed and reopened
RW in dev_write_bytes.
Have the caller pass the label_sector to the read
function so the read function can set the sector
field in the label struct, instead of having the
read function return a pointer to the label for
the caller to set the sector field.
Also have the read function return a flag indicating
to the caller that the scanned device was identified
as a duplicate pv.
wipe_lv knows it's going to write the device, so it
can open rw from the start. It was opening readonly,
and then dev_write needed to reopen it readwrite.
lvm uses a bcache block size of 128K. A bcache block
at the end of the metadata area will overlap the PEs
from which LVs are allocated. How much depends on
alignments. When lvm reads and writes one of these
bcache blocks to update VG metadata, it can also be
reading and writing PEs that belong to an LV.
If these overlapping PEs are being written to by the
LV user (e.g. filesystem) at the same time that lvm
is modifying VG metadata in the overlapping bcache
block, then the user's updates to the PEs can be lost.
This patch is a quick hack to prevent lvm from writing
past the end of the metadata area.
Native disk scanning is now both reduced and
async/parallel, which makes it comparable in
performance (and often faster) when compared
to lvm using lvmetad.
Autoactivation now uses local temp files to record
online PVs, and no longer requires lvmetad.
There should be no apparent command-level change
in behavior.
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/
with the --labelsector option. We probably don't
need all this code to support any value for this
option; it's unclear how, when, why it would be
used.
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.
This is a temporary hacky workaround to the problem of
reads going through bcache and writes not using bcache.
The write path wants to read parts of data that it is
incrementally writing to disk, but the reads (using
bcache) don't work because the writes are not in the
bcache. For now, add a dev to bcache before each attempt
to read it in case it's being used on the write path.
Create a new dev->bcache_fd that the scanning code owns
and is in charge of opening/closing. This prevents other
parts of lvm code (which do various open/close) from
interfering with the bcache fd. A number of dev_open
and dev_close are removed from the reading path since
the read path now uses the bcache.
With that in place, open(O_EXCL) for pvcreate/pvremove
can then be fixed. That wouldn't work previously because
of other open fds.
New label_scan function populates bcache for each device
on the system.
The two read paths are updated to get data from bcache.
The bcache is not yet used for writing. bcache blocks
for a device are invalidated when the device is written.
No longer use the external 'result' pointer internally to set up the
cached label. The callback _set_label_read_result() is now given the
internal label pointer directly
Callers that don't need the result are no longer required to pass a
label pointer into label_read().
Refactor the recent metadata-reading optimisation patches.
Remove the recently-added cache fields from struct labeller
and struct format_instance.
Instead, introduce struct lvmcache_vgsummary to wrap the VG information
that lvmcache holds and add the metadata size and checksum to it.
Allow this VG summary information to be looked up by metadata size +
checksum. Adjust the debug log messages to make it clear when this
shortcut has been successful.
(This changes the optimisation slightly, and might be extendable
further.)
Add struct cached_vg_fmtdata to format-specific vg_read calls to
preserve state alongside the VG across separate calls and indicate
if the details supplied match, avoiding the need to read and
process the VG metadata again.
Use similar logic as with text_vg_import_fd() and avoid repeated
parsing of same mda and its config tree for vgname_from_mda().
Remember last parsed vgname, vgid and creation_host in labeller
structure and if the metadata have the same size and checksum,
return this stored info.
TODO: The reuse of labeller struct is not ideal, some lvmcache API for
this functionality would be nicer.
All labellers always use the "private" (void *) field as the fmt pointer. Making
this fact explicit in the type of the labeller simplifies the label reporting
code which needs to extract the format. Moreover, it removes a number of
error-prone casts from the code.
Fix some memory leaks in error paths found by coverity.
Use C99 struct initialisers.
Move DEFS into configure.h.
Clean-ups to remove miscellaneous compiler warnings.
