Also finished migrating tests with test_relocations and test_exhaustion.
The issue I was running into when migrating these tests was a lack of
flexibility with what you could do with the block devices. It was
possible to hack in some hooks for things like bad blocks and power
loss, but it wasn't clean or easily extendable.
The solution here was to just put all of these test extensions into a
third block device, testbd, that uses the other two example block
devices internally.
testbd has several useful features for testing. Note this makes it a
pretty terrible block device _example_ since these hooks look more
complicated than a block device needs to be.
- testbd can simulate different erase values, supporting 1s, 0s, other byte
patterns, or no erases at all (which can cause surprising bugs). This
actually depends on the simulated erase values in ramdb and filebd.
I did try to move this out of rambd/filebd, but it's not possible to
simulate erases in testbd without buffering entire blocks and creating
an excessive amount of extra write operations.
- testbd also helps simulate power-loss by containing a "power cycles"
counter that is decremented every write operation until it calls exit.
This is notably faster than the previous gdb approach, which is
valuable since the reentrant tests tend to take a while to resolve.
- testbd also tracks wear, which can be manually set and read. This is
very useful for testing things like bad block handling, wear leveling,
or even changing the effective size of the block device at runtime.
The idea behind emubd (file per block), was neat, but doesn't add much
value over a block device that just operates on a single linear file
(other than adding a significant amount of overhead). Initially it
helped with debugging, but when the metadata format became more complex
in v2, most debugging ends up going through the debug.py script anyways.
Aside from being simpler, moving to filebd means it is also possible to
mount disk images directly.
Also introduced rambd, which keeps the disk contents in RAM. This is
very useful for testing where it increases the speed _significantly_.
- test_dirs w/ filebd - 0m7.170s
- test_dirs w/ rambd - 0m0.966s
These follow the emubd model of using the lfs_config for geometry. I'm
not convinced this is the best approach, but it gets the job done.
I've also added lfs_ramdb_createcfg to add additional config similar to
lfs_file_opencfg. This is useful for specifying erase_value, which tells
the block device to simulate erases similar to flash devices. Note that
the default (-1) meets the minimum block device requirements and is the
most performant.
