This just means a rewrite of the superblock entry with the new minor
version.
Though it's interesting to note, we don't need to rewrite the superblock
entry until the first write operation in the filesystem, an optimization
that is already in use for the fixing of orphans and in-flight moves.
To keep track of any outdated minor version found during lfs_mount, we
can carve out a bit from the reserved bits in our gstate. These are
currently used for a counter tracking the number of orphans in the
filesystem, but this is usually a very small number so this hopefully
won't be an issue.
In-device gstate tag:
[-- 32 --]
[1|- 11 -| 10 |1| 9 ]
^----^-----^--^--^-- 1-bit has orphans
'-----|--|--|-- 11-bit move type
'--|--|-- 10-bit move id
'--|-- 1-bit needs superblock
'-- 9-bit orphan count
This is a bit tricky since we need two different version of littlefs in
order to test for most compatibility concerns.
Fortunately we already have scripts/changeprefix.py for version-specific
symbols, so it's not that hard to link in the previous version of
littlefs in CI as a separate set of symbols, "lfsp_" in this case.
So that we can at least test the compatibility tests locally, I've added
an ifdef against the expected define "LFSP" to define a set of aliases
mapping "lfsp_" symbols to "lfs_" symbols. This is manual at the moment,
and a bit hacky, but gets the job done.
---
Also changed BUILDDIR creation to derive subdirectories from a few
Makefile variables. This makes the subdirectories less manual and more
flexible for things like LFSP. Note this wasn't possible until BUILDDIR
was changed to default to "." when omitted.
Christopher Haster