tests: try running tests over ramdisk

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

1 files changed, 1 insertions, 0 deletions

diff --git a/test/Makefile.in b/test/Makefile.in
index ccf1f31c2..de8e3a159 100644
--- a/test/Makefile.in
+++ b/test/Makefile.in
@@ -90,6 +90,7 @@ help:
 	@echo "  LVM_TEST_BACKING_DEVICE Set device used for testing (see also LVM_TEST_DIR)."
 	@echo "  LVM_TEST_CAN_CLOBBER_DMESG Allow to clobber dmesg buffer without /dev/kmsg. (1)"
 	@echo "  LVM_TEST_DEVDIR	Set to '/dev' to run on real /dev."
+	@echo "  LVM_TEST_PREFER_BRD	Prefer using brd (ramdisk) over loop for testing [1]."
 	@echo "  LVM_TEST_DIR		Where to create test files  [$(LVM_TEST_DIR)]."
 	@echo "  LVM_TEST_LOCKING	Normal (1), Cluster (3)."
 	@echo "  LVM_TEST_LVMETAD	Start lvmetad (1)."