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Adopted different strategy for hypothetical future configs

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Instead of writing every possible config that has the potential to be
useful in the future, stick to just writing the configs that we know are
useful, and error if we see any configs we don't understand.

This prevents unnecessary config bloat, while still allowing configs to
be introduced in a backwards compatible way in the future.

Currently unknown configs are treated as a mount error, but in theory
you could still try to read the filesystem, just with potentially
corrupted data. Maybe this could be behind some sort of "FORCE" mount
flag. littlefs must never write to the filesystem if it finds unknown
configs.

---

This also creates a curious case for the hole in our tag encoding
previously taken up by the OCOMPATFLAGS config. We can query for any
config > SIZELIMIT with lookupnext, but the OCOMPATFLAGS flag would need
an extra lookup which just isn't worth it.

Instead I'm just adding OCOMPATFLAGS back in. To support OCOMPATFLAGS
littlefs has to do literally nothing, so this is really more of a
documentation change. And who know, maybe OCOMPATFLAGS will have some
weird use case in the future...
This commit is contained in:
Christopher Haster
2023-12-08 14:03:56 -06:00
parent 337bdf61ae
commit 6ccd9eb598
6 changed files with 31 additions and 295 deletions
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14
scripts/dbgbtree.py
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@@ -12,18 +12,13 @@ TAG_NULL = 0x0000
TAG_CONFIG = 0x0000
TAG_MAGIC = 0x0003
TAG_VERSION = 0x0004
TAG_OCOMPATFLAGS = 0x0005
TAG_RCOMPATFLAGS = 0x0006
TAG_WCOMPATFLAGS = 0x0007
TAG_BLOCKSIZE = 0x0008
TAG_BLOCKCOUNT = 0x0009
TAG_NAMELIMIT = 0x000a
TAG_SIZELIMIT = 0x000b
TAG_UTAGLIMIT = 0x000c
TAG_UATTRLIMIT = 0x000d
TAG_STAGLIMIT = 0x000e
TAG_SATTRLIMIT = 0x000f
TAG_MDIRLIMIT = 0x0010
TAG_MTREELIMIT = 0x0011
TAG_GDELTA = 0x0100
TAG_GRMDELTA = 0x0100
TAG_NAME = 0x0200
@@ -168,18 +163,13 @@ def tagrepr(tag, w, size, off=None):
'shrub' if tag & TAG_SHRUB else '',
'magic' if (tag & 0xfff) == TAG_MAGIC
else 'version' if (tag & 0xfff) == TAG_VERSION
else 'ocompatflags' if (tag & 0xfff) == TAG_OCOMPATFLAGS
else 'rcompatflags' if (tag & 0xfff) == TAG_RCOMPATFLAGS
else 'wcompatflags' if (tag & 0xfff) == TAG_WCOMPATFLAGS
else 'blocksize' if (tag & 0xfff) == TAG_BLOCKSIZE
else 'blockcount' if (tag & 0xfff) == TAG_BLOCKCOUNT
else 'sizelimit' if (tag & 0xfff) == TAG_SIZELIMIT
else 'namelimit' if (tag & 0xfff) == TAG_NAMELIMIT
else 'utaglimit' if (tag & 0xfff) == TAG_UTAGLIMIT
else 'uattrlimit' if (tag & 0xfff) == TAG_UATTRLIMIT
else 'staglimit' if (tag & 0xfff) == TAG_STAGLIMIT
else 'sattrlimit' if (tag & 0xfff) == TAG_SATTRLIMIT
else 'mdirlimit' if (tag & 0xfff) == TAG_MDIRLIMIT
else 'mtreelimit' if (tag & 0xfff) == TAG_MTREELIMIT
else 'config 0x%02x' % (tag & 0xff),
' w%d' % w if w else '',
size)