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Port another optimization from pvscan -aay to vgchange -aay:
"pvscan: only add device args to dev cache"
This optimization avoids doing a full dev_cache_scan, and
instead populates dev-cache with only the devices in the
VG being activated.
This involves shifting the use of pvs_online files from
the hints interface up to the higher level label_scan
interface. This specialized label_scan is structured
around creating a list of devices from the pvs_online
files. Previously, a list of all devices was created
first, and then reduced based on the pvs_online files.
The initial step of listing all devices was slow when
thousands of devices are present on the system.
This optimization extends the previous optimization that
used pvs_online files to limit the devices that were
actually scanned (i.e. reading to identify the device):
"vgchange -aay: optimize device scan using pvs_online files"
When scanning configured /dev dir, avoid entring
directories with different filesystem.
This minimizes risk we will block on i.e. entring
directory with mount point.
Reporting non-PVs / "all devices" is only done by
pvs -a or pvdisplay -a, so avoid the work managing
a list of all devices in process_each_pv.
In the case when it's needed, use the results of
label_scan which already determines which devs
are not PVs.
sysconf() may also return -1 although rather theoretically.
Default to 4K when such case would happen.
Also in function call it just once and keep as static variable.
Ensure only nonNULL 'du' pointer is dereference altough the comment
to the last assign 'du' pointer already suggest 'NULL' case should not happen.
So just being explicit.
mer du
Some device id types can only be used with specific device major
numbers, so use this restriction to avoid some comparisions.
This is more efficient, and can avoid some incorrect matches.
pvid and vgid are sometimes a null-terminated string, and
other times a 'struct id', and the two types were often
cast between each other. When a struct id was cast to a char
pointer, the resulting string would not necessarily be null
terminated. Casting a null-terminated string id to a
struct id is fine, but is still avoided when possible.
A struct id is: int8_t uuid[ID_LEN]
A string id is: char pvid[ID_LEN + 1]
A convention is introduced to help distinguish them:
- variables and struct fields named "pvid" or "vgid"
should be null-terminated strings.
- variables and struct fields named "pv_id" or "vg_id"
should be struct id's.
- examples:
char pvid[ID_LEN + 1];
char vgid[ID_LEN + 1];
struct id pv_id;
struct id vg_id;
Function names also attempt to follow this convention.
Avoid casting between the two types as much as possible,
with limited exceptions when known to be safe and clearly
commented.
Avoid using variations of strcpy and strcmp, and instead
use memcpy/memcmp with ID_LEN (with similar limited
exceptions possible.)
sysfs-based multipath component detection quit if a
device had multiple holders, and in this case would
fail to detect a device was an mpath component.
related to config settings:
obtain_device_info_from_udev (controls if lvm gets
a list of devices from readdir /dev or from libudev)
external_device_info_source (controls if lvm asks
libudev for device information)
. Make the obtain_device_list_from_udev setting
affect only the choice of readdir /dev vs libudev.
The setting no longer controls if udev is used for
device type checks.
. Change obtain_device_list_from_udev default to 0.
This helps avoid boot timeouts due to slow libudev
queries, avoids reported failures from
udev_enumerate_scan_devices, and avoids delays from
"device not initialized in udev database" errors.
Even without errors, for a system booting with 1024 PVs,
lvm2-pvscan times improve from about 100 sec to 15 sec,
and the pvscan command from about 64 sec to about 4 sec.
. For external_device_info_source="none", remove all
libudev device info queries, and use only lvm
native device info.
. For external_device_info_source="udev", first check
lvm native device info, then check libudev info.
. Remove sleep/retry loop when attempting libudev
queries for device info. udev info will simply
be skipped if it's not immediately available.
. Only set up a libdev connection if it will be used by
obtain_device_list_from_udev/external_device_info_source.
. For native multipath component detection, use
/etc/multipath/wwids. If a device has a wwid
matching an entry in the wwids file, then it's
considered a multipath component. This is
necessary to natively detect multipath
components when the mpath device is not set up.
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.
This case happens when i.e. we convert LV to another type,
when we change existing LV into a different type - so change
to debug level and avoid confusing users with message about
Device path not match.
We may eventually enhnace caching code to drop cached info
after taking lock and reading VG.
