These docs are under active development and cover the v0.20 Kobicha security model.
Peios Learn
On this page
Print Full Specification
§1.4

Compatibility

§1.4.1 Format compatibility

LCS has one hard external format compatibility requirement: registry.pol. The registry MUST support every data type, path semantic, and operation that registry.pol can express -- the binary format used by Active Directory Group Policy to deliver configuration to domain-joined machines. registry.pol compatibility is the reason the registry exists.

LCS is not responsible for parsing registry.pol files. Parsing is a userspace concern -- the Group Policy client reads registry.pol and translates its contents into registry syscalls. LCS provides the data model and operations necessary to faithfully represent everything registry.pol can express.

registry.pol drives the following format decisions:

  • Value types. The full Windows registry value type set (REG_SZ, REG_EXPAND_SZ, REG_BINARY, REG_DWORD, REG_DWORD_BIG_ENDIAN, REG_LINK, REG_MULTI_SZ, REG_QWORD, REG_NONE) MUST be supported. LCS treats values as opaque typed blobs -- it stores the type tag but does not interpret the data, except REG_LINK which triggers symlink resolution.

  • Path format. Registry paths use backslash separators and are case-preserving, case-insensitive. registry.pol paths follow this convention.

  • Access right bit positions. Registry-specific access rights (KEY_QUERY_VALUE, KEY_SET_VALUE, KEY_CREATE_SUB_KEY, etc.) occupy the same bit positions as Windows registry access rights. This ensures Security Descriptors containing registry ACEs are binary-compatible. The bit positions are defined in the Access Rights section of this specification; the SD binary format itself is specified by KACS.

No other format parity with Windows is claimed or required by LCS. SD binary format compatibility is a KACS guarantee, not an LCS one.

§1.4.2 Architectural divergences

LCS is modelled on the Windows Configuration Manager but diverges in several areas. These are intentional design decisions, not compatibility gaps.

Divergence Windows LCS Rationale
Backing store Kernel-internal hive files Userspace sources via RSI Enables different storage backends without kernel changes. Storage is a source concern, not a kernel concern.
Hive routing Fixed set of predefined hives Extensible -- any source can register any hive name at runtime Supports role installation, testing, and future hive types without kernel changes.
Layer system No equivalent. registry.pol is applied by flattening values. Precedence-ordered layers with tombstones. Reads resolve at query time. Automatic revert on layer deletion (no-tattoo semantics). Role uninstall and GP removal are layer deletion.
Change observation RegNotifyChangeKeyValue is single-shot (must re-register after each event) Persistent watches (remain armed until fd closes) Eliminates the race window between notification and re-registration where changes can be missed. Matches the inotify model.
Key identity Hive cell offsets (internal) GUIDs (128-bit, kernel-assigned, source-persisted) Stable across storage reorganisation. Consistent with Peios's identifier model.
Forward slash Not accepted in registry paths Accepted on input, normalised to backslash Convenience for Linux users. The canonical form is always backslash.
Case comparison RtlCompareUnicodeString Unicode Simple Case Folding (CaseFolding.txt, status S and C entries) Practical compatibility with Windows behaviour, not byte-identical in all edge cases. Fixed one-to-one codepoint mapping with no locale dependency.

§1.4.3 Excluded Windows features

The following Windows registry features have been evaluated and excluded from LCS.

Feature Why excluded
Key classes The "class" parameter in RegCreateKeyEx is documented as reserved by Microsoft. No known consumer.
RegOverridePredefKey Per-process key redirection. COM-specific. Would require unbounded per-process state in the kernel. Private hives and private layers cover the legitimate use cases.
WoW64 redirection 32/64-bit registry key splitting. Peios has no 32-bit compatibility concern.
HKEY_CLASSES_ROOT merged overlay Merges HKLM and HKCU Software\Classes. COM-specific. No Peios equivalent.