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attrs: Reduced UATTR/SATTR range down to 7-bits

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It would be nice to have a full 8-bit range for both user attrs and
system attrs, for both backwards compatibility and maximizing the
available attr space, but I think it just doesn't make sense from an API
perspective.

Sure we could finagle the user/sys bit into a flags argument, or provide
separate lfsr_getuattr/getsattr functions, but asking users to use a
9-bit int for higher-level operations (dynamic attrs, iteration, etc) is
a bit much...

So this reduces the two attr ranges down to 7-bits, requiring 8-bits
total to store all possible attr types in the current system:

  TAG_ATTR      0x0400  v--- -1-a -aaa aaaa
  TAG_UATTR     0x04aa  v--- -1-- -aaa aaaa
  TAG_SATTR     0x05aa  v--- -1-1 -aaa aaaa

This really just affects scripts, since we haven't actually implemented
attributes yet.

Worst case we still have the 9-bit encoding space carved out, so we can
always add an additional set of attrs in the future if we start running
into attr pressure.

Or, you know, just turn on the subtype leb128 encoding the 8th subtype
bit is reserved for. Then you'd only be limited by internal driver
details, probably 24-bits per attr range if we make tags 32-bits
internally. Though this would probably come with quite a code cost...
This commit is contained in:
Christopher Haster
2024-08-21 14:19:38 -05:00
parent 2407cc2ae5
commit 4d8bfeae71
9 changed files with 2200 additions and 2223 deletions
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18
scripts/dbgbtree.py
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@@ -35,8 +35,9 @@ TAG_MDIR = 0x0315 # 0x0314 v--- --11 ---1 -1rr
TAG_MTREE = 0x031c # 0x031c v--- --11 ---1 11rr
TAG_DID = 0x0320 # 0x0320 v--- --11 --1- ----
TAG_BRANCH = 0x032c # 0x032c v--- --11 --1- 11rr
TAG_UATTR = 0x0400 # 0x04aa v--- -1-a -aaa aaaa
TAG_SATTR = 0x0600 # 0x06aa v--- -11a -aaa aaaa
TAG_ATTR = 0x0400 ## 0x04aa v--- -1-a -aaa aaaa
TAG_UATTR = 0x0400 # 0x04aa v--- -1-- -aaa aaaa
TAG_SATTR = 0x0500 # 0x05aa v--- -1-1 -aaa aaaa
TAG_SHRUB = 0x1000 ## 0x1kkk v--1 kkkk -kkk kkkk
TAG_ALT = 0x4000 ## 0x4kkk v1cd kkkk -kkk kkkk
TAG_B = 0x0000
@@ -213,16 +214,11 @@ def tagrepr(tag, w=None, size=None, off=None):
else 'struct 0x%02x' % (tag & 0xff),
' w%d' % w if w else '',
' %s' % size if size is not None else '')
elif (tag & 0x6e00) == TAG_UATTR:
return '%suattr 0x%02x%s%s' % (
elif (tag & 0x6e00) == TAG_ATTR:
return '%s%sattr 0x%02x%s%s' % (
'shrub' if tag & TAG_SHRUB else '',
((tag & 0x100) >> 1) | (tag & 0xff),
' w%d' % w if w else '',
' %s' % size if size is not None else '')
elif (tag & 0x6e00) == TAG_SATTR:
return '%ssattr 0x%02x%s%s' % (
'shrub' if tag & TAG_SHRUB else '',
((tag & 0x100) >> 1) | (tag & 0xff),
's' if tag & 0x100 else 'u',
((tag & 0x100) >> 1) ^ (tag & 0xff),
' w%d' % w if w else '',
' %s' % size if size is not None else '')
elif tag & TAG_ALT: