MagnitudeOS/littlefs
1
0
Fork 0
forked from Imagelibrary/littlefs
Code Pull Requests Activity

Reworked config tags, adopted rflags/wflags/oflags

Browse Source 
The biggest change here is the breaking up of the FLAGS config into
RFLAGS/WFLAGS/OFLAGS. This is directly inspired by, and honestly not
much more than a renaming, of the compat/ro_compat/incompat flags found
in Linux/Unix/POSIX filesystems.

I think these were first introduced in ext2? But I need to do a bit more
research on that.

RFLAGS/WFLAGS/OFLAGS provide a much more flexible, and extensible,
feature flag mechanism than the previous minor version bumps.

The (re)naming of these flags is intended to make their requirements
more clear. In order to do the relevant operation, you must understand
every flag set in the relevant flag:

- RFLAGS / incompat flags - All flags must be understood to read the
  filesystem, if not understood the only possible behavior is to fail.

- WFLAGS / ro-compat flags - All flags must be understood to write to the
  filesystem, if not understood the filesystem may be mounted read-only.

- OFLAGS / compat flags - Optional flags, if not understood the relevant
  flag must be cleared before the filesystem can be written to, but other
  than that these flags can mostly be ignored.

Some hypothetical littlefs examples:

- RFLAGS / incompat flags - Transparent compression

  Is this the same as a major disk-version break? Yes kinda? An
  implementation that doesn't understand compression can't read the
  filesystem.

  On the other hand, it's useful to have a filesystem that can read both
  compressed and uncompressed variants.

- WFLAGS / ro-compat flags - Closed block-map

  The idea behind a closed block-map (currently planned), is that
  littlefs maintains in global space a complete mapping of all blocks in
  use by the filesystem.

  For such a mapping to remain consistent means that if you write to the
  filesystem you must understand the closed block-map. Or in other
  words, if you don't understand the closed block-map you must not write
  to the filesystem.

  Reading, on the other hand, can ignore many such write-related
  auxiliary features, so the filesystem can still be read from.

- OFLAGS / compat flags - Global checksums

  Global checksums (currently planned) are extra checksums attached to
  each mdir that when combined self-validate the filesystem.

  But if you don't understand global checksums, you can still read and
  write the filesystem without them. The only catch is that when you write
  to the filesystem, you may end up invalidating the global checksum.

  Clearing the global checksum bit in the OFLAGS is a cheap way to
  signal that the global checksum is no longer valid, allowing you to
  still write to the filesystem without this optional feature.

Other tweaks to note:

- Renamed BLOCKLIMIT/DISKLIMIT -> BLOCKSIZE/BLOCKCOUNT

  Note these are still the _actual_ block_size/block_count minus 1. The
  subtle difference here was the original reason for the name change,
  but after working with it for a bit, I just don't think new, otherwise
  unused, names are worth it.

  The minus 1 stays, however, since it avoids overflow issues at
  extreme boundaries of powers of 2.

- Introduces STAGLIMIT/SATTRLIMIT, sys-attribute parallels to
  UTAGLIMIT/UATTRLIMIT.

  These may be useful if only uattrs are supported, or vice-versa.

- Dropped UATTRLIMIT/SATTRLIMIT to 255 bytes.

  This feels extreme, but matches NAMELIMIT. These _should_ be small,
  and limiting the uattr/sattr size to a single-byte leads to really
  nice packing of the utag+uattrsize in a single integer.

  This can always be expanded in the future if this limit proves to be a
  problem.

- Renamed MLEAFLIMIT -> MDIRLIMIT and (re?)introduced MTREELIMIT.

  These may be useful to limiting the mtree when needed, though it's not
  clear the exact use case quite yet.
This commit is contained in:
Christopher Haster
2023-10-25 01:58:23 -05:00
parent 6dcdf1ed61
commit bfc8021176
6 changed files with 429 additions and 269 deletions
Download Patch File Download Diff File Expand all files Collapse all files

36
scripts/dbgrbyd.py
View File

@@ -21,16 +21,19 @@ TAG_NULL = 0x0000
TAG_CONFIG = 0x0000
TAG_MAGIC = 0x0003
TAG_VERSION = 0x0004
TAG_FLAGS = 0x0005
TAG_CKSUMTYPE = 0x0006
TAG_REDUNDTYPE = 0x0007
TAG_BLOCKLIMIT = 0x0008
TAG_DISKLIMIT = 0x0009
TAG_MLEAFLIMIT = 0x000a
TAG_RFLAGS = 0x0005
TAG_WFLAGS = 0x0006
TAG_OFLAGS = 0x0007
TAG_BLOCKSIZE = 0x0008
TAG_BLOCKCOUNT = 0x0009
TAG_NAMELIMIT = 0x000a
TAG_SIZELIMIT = 0x000b
TAG_NAMELIMIT = 0x000c
TAG_UTAGLIMIT = 0x000d
TAG_UATTRLIMIT = 0x000e
TAG_UTAGLIMIT = 0x000c
TAG_UATTRLIMIT = 0x000d
TAG_STAGLIMIT = 0x000e
TAG_SATTRLIMIT = 0x000f
TAG_MDIRLIMIT = 0x0010
TAG_MTREELIMIT = 0x0011
TAG_GSTATE = 0x0100
TAG_GRM = 0x0100
TAG_NAME = 0x0200
@@ -144,16 +147,19 @@ 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 'flags' if (tag & 0xfff) == TAG_FLAGS
else 'cksumtype' if (tag & 0xfff) == TAG_CKSUMTYPE
else 'redundtype' if (tag & 0xfff) == TAG_REDUNDTYPE
else 'blocklimit' if (tag & 0xfff) == TAG_BLOCKLIMIT
else 'disklimit' if (tag & 0xfff) == TAG_DISKLIMIT
else 'mleaflimit' if (tag & 0xfff) == TAG_MLEAFLIMIT
else 'rflags' if (tag & 0xfff) == TAG_RFLAGS
else 'wflags' if (tag & 0xfff) == TAG_WFLAGS
else 'oflags' if (tag & 0xfff) == TAG_OFLAGS
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)