These provide useful file powerloss testing that scales linearly as long
as progress can be made. They can still struggle a bit, especially with
relocations which often fail to make progress, but they are _much_ better
than the O(n^2) simulation-based fuzz tests:
- test_files_pl_fuzz - 258734 pls
- test_relocations_pl_fuzz - 928638 pls
Our current problem with simulation-based fuzz testing is that we lose
the simulation on powerloss. We could brute force this, repeatedly
rerunning the simulation until it succeeds, but this grows O(n^2) with
our linear powerloss heuristic.
To avoid this, test_*_pl_fuzz doesn't bother with a simulation, instead
relying on internal asserts to catch bugs. This is less rigorous, but
realistically probably going to catch any powerloss related issues.
Some notes:
- We need to store some state on disk. If we don't we will still end up
with O(n^2) behavior because we simply don't know how many operations
we've accomplished so far.
- Since we rely on file operations to store our test state, this makes
this approach incompatible with the dir tests, which assume file
operations may not yet be implemented.
We still use O(n^2) powerloss testing in test_dirs, just with a small
number of directories.
- It's tempting to try to store a full simulation on disk. But you
would quickly run into atomicity issues with the simulation itself.
Powerloss resilience is tricky!
- We can at least store a checksum in the files (currently just mod 26)
to check that the file itself was not corrupted. This doesn't protect
against swapped data though.
---
Also, a bit of a tangent, but I needed to add -Wno-format-overflow to
the test flags to avoid an annoying invalid format-overlow warning:
struct lfs_info info;
char name[256];
if (strlen(info.name) < 100) { // can't overflow!?
sprintf(name, "test/%s", info.name); // <--
}
warning: '%s' directive writing up to 255 bytes into a region of size
251 [-Wformat-overflow=]
This seems like a GCC bug, because as far as I can tell there is no way
to signal or hint that the size is in bounds without just disabling the
warning completely...
Christopher Haster
3b33c33339