Changed most references to crc/csum -> cksum
The reason for this is to move away from the idea that littlefs is strictly bound to CRCs and make the code more welcoming to other checksum types, such as SHA256, etc. Of course, changing the name doesn't really do anything. littlefs actually _is_ strictly bound to CRCs in a couple ways that other filesystems aren't. These would need to have workarounds for other checksum types: - We leverage the parity-preserving nature of (some) CRCs to not have to also calculate the parity of metadata in rbyd commits. - We leverage the linearity of CRCs to retroactively flip the perturb bit in the cksum tag without needing to recalculate the checksum. Though the fact we need to do this is because of how we use parity above, so this may just not be needed for non-CRC checksums. - The plans for global-CRCs (not yet implemented) rely heavily on the mathematical properties of CRC polynomials. This doesn't mean global-CRCs can't work with other checksums, you would just need to find a different type of polynomial.
This commit is contained in:
Christopher Haster
+32
-32
@@ -38,8 +38,8 @@ TAG_DID = 0x0307
|
||||
TAG_UATTR = 0x0400
|
||||
TAG_SATTR = 0x0500
|
||||
TAG_ALT = 0x4000
|
||||
TAG_CRC = 0x2000
|
||||
TAG_FCRC = 0x2100
|
||||
TAG_CKSUM = 0x2000
|
||||
TAG_FCKSUM = 0x2100
|
||||
|
||||
|
||||
|
||||
@@ -109,7 +109,7 @@ def fromtag(data):
|
||||
def popc(x):
|
||||
return bin(x).count('1')
|
||||
|
||||
def xxd(data, width=16, crc=False):
|
||||
def xxd(data, width=16):
|
||||
for i in range(0, len(data), width):
|
||||
yield '%-*s %-*s' % (
|
||||
3*width,
|
||||
@@ -169,13 +169,13 @@ def tagrepr(tag, w, size, off=None):
|
||||
tag & 0xff,
|
||||
' w%d' % w if w else '',
|
||||
size)
|
||||
elif (tag & 0xff00) == TAG_CRC:
|
||||
return 'crc%x%s %d' % (
|
||||
elif (tag & 0xff00) == TAG_CKSUM:
|
||||
return 'cksum%x%s %d' % (
|
||||
1 if tag & 0x1 else 0,
|
||||
' 0x%x' % w if w > 0 else '',
|
||||
size)
|
||||
elif tag == TAG_FCRC:
|
||||
return 'fcrc%s %d' % (
|
||||
elif tag == TAG_FCKSUM:
|
||||
return 'fcksum%s %d' % (
|
||||
' 0x%x' % w if w > 0 else '',
|
||||
size)
|
||||
elif tag & 0x4000:
|
||||
@@ -194,7 +194,7 @@ def tagrepr(tag, w, size, off=None):
|
||||
def dbg_log(data, block_size, rev, off, weight, *,
|
||||
color=False,
|
||||
**args):
|
||||
crc = crc32c(data[0:4])
|
||||
cksum = crc32c(data[0:4])
|
||||
|
||||
# preprocess jumps
|
||||
if args.get('jumps'):
|
||||
@@ -444,20 +444,20 @@ def dbg_log(data, block_size, rev, off, weight, *,
|
||||
|
||||
j = j_
|
||||
v, tag, w, size, d = fromtag(data[j_:])
|
||||
if v != (popc(crc) & 1):
|
||||
notes.append('v!=%x' % (popc(crc) & 1))
|
||||
crc = crc32c(data[j_:j_+d], crc)
|
||||
if v != (popc(cksum) & 1):
|
||||
notes.append('v!=%x' % (popc(cksum) & 1))
|
||||
cksum = crc32c(data[j_:j_+d], cksum)
|
||||
j_ += d
|
||||
|
||||
# take care of crcs
|
||||
# take care of cksums
|
||||
if not tag & 0x4000:
|
||||
if (tag & 0xff00) != TAG_CRC:
|
||||
crc = crc32c(data[j_:j_+size], crc)
|
||||
# found a crc?
|
||||
if (tag & 0xff00) != TAG_CKSUM:
|
||||
cksum = crc32c(data[j_:j_+size], cksum)
|
||||
# found a cksum?
|
||||
else:
|
||||
crc_ = fromle32(data[j_:j_+4])
|
||||
if crc != crc_:
|
||||
notes.append('crc!=%08x' % crc)
|
||||
cksum_ = fromle32(data[j_:j_+4])
|
||||
if cksum != cksum_:
|
||||
notes.append('cksum!=%08x' % cksum)
|
||||
j_ += size
|
||||
|
||||
# evaluate trunks
|
||||
@@ -499,7 +499,7 @@ def dbg_log(data, block_size, rev, off, weight, *,
|
||||
else ''))
|
||||
|
||||
# show in-device representation, including some extra
|
||||
# crc/parity info
|
||||
# cksum/parity info
|
||||
if args.get('device'):
|
||||
print('%s%8s %*s%*s %-47s %08x %x%s' % (
|
||||
'\x1b[90m' if color and j >= off else '',
|
||||
@@ -514,8 +514,8 @@ def dbg_log(data, block_size, rev, off, weight, *,
|
||||
for i in range(min(m.ceil(size/4), 3)))[:23]
|
||||
if not args.get('no_truncate')
|
||||
and not tag & 0x4000 else ''),
|
||||
crc,
|
||||
popc(crc) & 1,
|
||||
cksum,
|
||||
popc(cksum) & 1,
|
||||
'\x1b[m' if color and j >= off else ''))
|
||||
|
||||
# show on-disk encoding of tags
|
||||
@@ -852,8 +852,8 @@ def main(disk, blocks=None, *,
|
||||
# first figure out which block as the most recent revision
|
||||
def fetch(data, trunk):
|
||||
rev = fromle32(data[0:4])
|
||||
crc = 0
|
||||
crc_ = crc32c(data[0:4])
|
||||
cksum = 0
|
||||
cksum_ = crc32c(data[0:4])
|
||||
off = 0
|
||||
j_ = 4
|
||||
trunk_ = 0
|
||||
@@ -865,25 +865,25 @@ def main(disk, blocks=None, *,
|
||||
trunkoff = None
|
||||
while j_ < len(data) and (not trunk or off <= trunk):
|
||||
v, tag, w, size, d = fromtag(data[j_:])
|
||||
if v != (popc(crc_) & 1):
|
||||
if v != (popc(cksum_) & 1):
|
||||
break
|
||||
crc_ = crc32c(data[j_:j_+d], crc_)
|
||||
cksum_ = crc32c(data[j_:j_+d], cksum_)
|
||||
j_ += d
|
||||
if not tag & 0x4000 and j_ + size > len(data):
|
||||
break
|
||||
|
||||
# take care of crcs
|
||||
# take care of cksums
|
||||
if not tag & 0x4000:
|
||||
if (tag & 0xff00) != TAG_CRC:
|
||||
crc_ = crc32c(data[j_:j_+size], crc_)
|
||||
# found a crc?
|
||||
if (tag & 0xff00) != TAG_CKSUM:
|
||||
cksum_ = crc32c(data[j_:j_+size], cksum_)
|
||||
# found a cksum?
|
||||
else:
|
||||
crc__ = fromle32(data[j_:j_+4])
|
||||
if crc_ != crc__:
|
||||
cksum__ = fromle32(data[j_:j_+4])
|
||||
if cksum_ != cksum__:
|
||||
break
|
||||
# commit what we have
|
||||
off = trunkoff if trunkoff else j_ + size
|
||||
crc = crc_
|
||||
cksum = cksum_
|
||||
trunk_ = trunk__
|
||||
weight = weight_
|
||||
|
||||
|
||||
Reference in New Issue
Block a user