These simply imply LFS_O_FLUSH/SYNC on all open writable files.
LFS_M_SYNC is equivalent to MS_SYNCHRONOUS in Linux/etc, while
LFS_M_FLUSH is just provided for consistency.
As pure conveniences, these may seem a bit out of scope for littlefs,
except they are _very_ cheap:
code stack
before: 36356 2664
after: 36356 (+0.0%) 2664 (+0.0%)
Ok, they're not _completely_ free! It just turns out they cost 8 bytes,
and a bit of simplification around flag checking in lfsr_mount saved
8 bytes:
code stack
before: 36356 2664
m_flush/sync: 36364 (+0.0%) 2664 (+0.0%)
mount-no-mask: 36356 (+0.0%) 2664 (+0.0%)
Christopher Haster
b37bff377b