actiondfs: simplify cached directories, inode ownership, and backing files - #26
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Continue merged #26 with 30 separately reviewable actiondfs commits. Prevent unprivileged staged operations from triggering the Linux notify_change BUG on privilege removal; serialize staged writes and copy_file_range, preserve and correctly clear setuid/setgid bits, honor backing mount idmaps, reject malformed protobuf keys, and sanitize forwarded ATTR_OPEN. Simplify staged dentry publication, inode classification and ownership, CAS and staged path references, cached-child allocation, generation locking, and protobuf fixed-width decoding. The actiondfs implementation removes 28 net lines and adds focused VM regressions for non-root privileged-file creation, truncation, copy_file_range, and O_TRUNC. Validation: all 66 supported cross-architecture Bazel build targets and repository tests; standalone timing-parser test; production and instrumented macOS Virtualization.framework VM suites; fresh LLVM VM smoke with 2,017 warmup and 2,106 measured actions; all five GitHub Actions checks passed. Matched 1,998-action CI benchmarks: Linux actiond 304.743s / native 313.029s = 0.974x versus main 1.055x; Windows actiond 348.083s / native 373.566s = 0.932x versus main 1.005x. Both VM timing reports are refreshed.
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Continue #25 with 25 separately reviewable actiondfs cleanups. Derive inode and merged-directory state from cached children, use RCU for immutable directory-cache hits, search only cached input directories, borrow backing dentries and staged copy files, transfer root-node ownership to root inodes, reduce each superblock allocation from 128 to 96 bytes, allocate unhashed roots directly, publish staged backing dentries before inode insertion, initialize locks only for loadable inputs, and remove unnecessary ancestor zeroing, repeated inode classification, blob checks, synthetic symlink digests, protobuf copies, cache cleanup branches, and released-file state resets.
Validation: all 66 supported Bazel targets, both repository test suites, the standalone timing-parser test, production and instrumented Virtualization.framework VM end-to-end tests, and two fresh llvm-tblgen VM smoke runs with identical 2,106 remote actions (88.494s and 86.002s; previous run 74.995s). Warmups ranged from 63.992s to 83.160s, indicating host contention; compare matched Linux and Windows CI actiond/native results for performance changes. e2e/LLVM_VM_SMOKE_TIMINGS.md contains the exact counters and both measurements.