We don't directly mount the underlying devices for each mount because
the kernel notices multiple mounts and doesn't setup a new super block
for each.
Previously the script used loopback devices to create the local shared
block construct 'cause it was easy. This introduced corruption of
blocks that saw concurrent read and write IOs. The buffered kernel file
IO paths that loopback eventually degrades into by default (via splice)
could have buffered readers copying out of pages without the page lock
while writers modified the page. This manifest as occasional crc
failure of blocks that we knowingly issue concurrent reads and writes to
from multiple mounts (the quorum and super blocks).
This changes the script to use device-mapper linear passthrough devices.
Their IOs don't hit a caching layer and don't provide an opportunity to
corrupt blocks.
Signed-off-by: Zach Brown <zab@versity.com>
The README in tests/ had gone a bit stale. While it was originally
written to be a README.md displayed in the github repo, we can
still use it in place as a quick introduction to the tests.
Signed-off-by: Zach Brown <zab@versity.com>
The first commit of the scoutfs-tests suite which uses multiple mounts
on one host to test multi-node scoutfs.
Signed-off-by: Zach Brown <zab@versity.com>
