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No point to start building lvm without this header file.
Although there could be 'some point' in supporting standalone build
of 'just' libdm where the libaio might be avoided.
TODO: think about configure option for building libdm only.
Unfortunatelly on kernels <4.16 lvm2 can't user brd ramdisks
for backend device as number of test is failing with this kernel
message:
device-mapper: ioctl: can't change device type after initial table load.
caused by DAX request-based handling, and lvm2 tries to replace device
with backend 'error' bio-based device and such table reload is being
rejected.
So ATM keep ramdisk only on most recent kernel to experiment a bit,
for older machines just stay safe and keep old slower loop backend.
While newer system can detect need for 4K mkfs, on older test machines
running test suite over 4k is reporting problems.
Some more generic solution is needed thought.
When test happens to run in tmpfs, it cannot use O_DIRECT (unsupported
with tmpfs).
CHECKME: unsure if detection of tmpfs is 'valid' but kind of works and
is very simple.
As Makefiles already do use target with name 'device-mapper'
rename this new device-mapper dir to non-conflicting name.
We also seem to already use '_' in other dir names.
Also rename device_mapper/Makefile to source for generating Makefile.in
so we can use it for build in other source dirs properly.
It's very hard to use some 'non-recurive' Makefiles with
rest of system running 'recursively'.
So ATM drop inclusion of subdir makefile and add support
for 2 new top-level targets:
unit-test (builds test/unit dir)
run-unit-test (build & run test/unit/unit-test run)
Just like 52656c89fd
when now cache is compiled in 'unditionally'.
This patch is actually enforce by changes in
commit: 2bc896f2a3
where CACHE value is not set anymore.
If the test does not need root, it can use 'SKIP_ROOT_DM_CHECK'.
For such test no actions needed root to initilize DM devices and
nodes will be take and test can check i.e. functional unit tests.
Usage of dm_delay looks to be slowing not just 'delayed' portion
of device, but due to the fact it's also slows down ANY flush
operation on such device it's overal speed impact is huge.
In some case we can however user other methods to slowdown disk writes,
in case of old dm 'mirror' target we can throttle I/O of mirror
synchronisation giving the next commands enough time to test couple
race conditions.
Usage:
throttle_dm_mirror [percentage]
Thtrottle down sync speed (lowest is '1' which is also default when
unspecified)
restore_dm_mirror
Restores the value of throttling before call of 'throttle_dm_mirror'
Usually it should '100'
Currently usage of loop device over backend file in ramdisk (tmpfs)
is actually causing unnecassary memory consution, since just
reading such loop device is causing RAM provisioning.
This patch add another possible way how to use ramdisk directly
through 'brd' device when possible (and allowed).
This however has it's limitation as well - brd does not support
TRIM, so the only way how to erase is to remove brd module ??
Alse there is 4K sector size limitation imposed by ramdisk.
Anyway - for some mirror test that were using large amount of
disk space (tens of MB) this brings noticable speed boost.
(But could be worth to solve the slowness of loop in kernel?)
To prevent using 'brd' for testing set LVM_TEST_PREFER_BRD=0
like this:
make check_local LVM_TEST_PREFER_BRD=0
This test can't use brd (ramdisk) as backend since for some
weird reason lsblk is not listing these device.
TODO: test could be probably rewritten to avoid using lsblk somehow??
When the backend device supports only 4K blocks (like ramdisk)
we cannot use for testing any smaller blocksize.
So recalc test for 4K extent size.
We may possibly introduce one list extra test that
can be executed on devices with 512b sectors to
check lvm2 support those min extent sizes...
ATM it's a bit ugly to enforce flushing of 'stdio' here, but works as quick
hot-fix.
log_print*() is using buffered I/O.
But for pooling with typical 1s interval this may take a while before
buffer about continues progress gets flushed.
So ATM fflush().
TODO: either add log_print*_with_flush() or maybe directly use just
line buffering with log_print() and only log_debug() keep using buffered
I/O mode.
md devices using an older superblock version have
superblocks at the end of the md device. For commands
that skip reading the end of devices during filtering,
the md component devs will be scanned, and will appear
as duplicate PVs to the original md device. Remove
these md components from the list of unused duplicate
devices, so they are treated as if they had been
ignored during filtering. This avoids the restrictions
that are placed on using PVs with duplicates.
