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The device-mapper directory now holds a copy of libdm source. At
the moment this code is identical to libdm. Over time code will
migrate out to appropriate places (see doc/refactoring.txt).
The libdm directory still exists, and contains the source for the
libdevmapper shared library, which we will continue to ship (though
not neccessarily update).
All code using libdm should now use the version in device-mapper.
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.
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/
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'
