This saves a bit of rbyd overhead, since these almost always come
together.
Perhaps more interesting, it carves out space for storing mroot-anchor
redundancy information. This uses the lowest two bits of the GEOMETRY
tag to indicate how many redundant blocks belong to the mroot-anchor:
LFSR_TAG_GEOMETRY 0x0008 v--- ---- ---- 1-rr
This solves a bit of a hole in our redundancy encoding. The plan is for
this info to be stored in the lowest two bits of every pointer, but the
mroot-anchor doesn't really have a pointer.
Though this is just future plans. Right now the redundancy information
is unused. Current implementations should use the GEOMETRY tag 0x0009,
which you may notice implied redundancy level-1. This matches our
current 2-block per mdir default.
Geometry attr encoding:
.---+---+---+---. tag (0x0008+r): 1 be16 2 bytes
|x0008+r| 0 |siz| weight (0): 1 leb128 1 byte
+---+---+---+---+ size: 1 leb128 1 byte
| block_size | block_size: 1 leb128 <=4 bytes
+---+- -+- -+- -+- -.
| block_count | block_count: 1 leb128 <=5 bytes
'---+- -+- -+- -+- -' total: <=13 bytes
Code changes:
code stack
before: 34092 2880
after: 34040 (-0.2%) 2880 (+0.0%)
Christopher Haster
9366674416