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Diffstat (limited to '9ns/docs/DESIGN.md')
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diff --git a/9ns/docs/DESIGN.md b/9ns/docs/DESIGN.md index 1d66387..6b1b80c 100644 --- a/9ns/docs/DESIGN.md +++ b/9ns/docs/DESIGN.md @@ -114,6 +114,31 @@ posted name reaches that server's whole 9P tree, and nothing is connected until something walks. XDG_RUNTIME_DIR unset is fatal before anything is forked (the registry is not guessable; no `/tmp` fallback). +A registry entry that is a **directory** is served the same way the root +is: a synthetic directory (its node id under the reserved index +`synth_index`, the slot in the low bits) listing the real directory's +entries, dialing the sockets found inside on walk and recursing into +further directories — up to `max_synth_depth` (8) levels, bounded by +`max_synth_dirs` (64) synthetic nodes per 9ns process. This is how +multi-service providers organize themselves (zmx posts its sessions +under `zmx/<name>`), the plan9port `mntgen` shape: one tree, many +mounts, each entry a mount point. Non-socket, non-directory entries +inside a directory answer EIO on walk, exactly like a plain file in the +registry itself; a directory's slots are freed when the kernel forgets +the dentry. + +A synthetic node's slot comes back through FORGET, and the kernel sends +most of them as `BATCH_FORGET`, whose header `nodeid` is 0 and whose +body carries one `(nodeid, nlookup)` per forgotten node — for any mix of +owners. The dispatcher therefore cannot route a batch by its header the +way it routes every other request: `distributeForgets` unpacks the body +and hands each entry to its owner (synthetic root, synthetic +subdirectory or per-mount bridge). Routing the batch whole instead loses +every entry in it, so the 64 slots leak and a subdirectory served once +answers EIO forever. The forgets themselves arrive on the kernel's +schedule, not at `close`, so a slot may take a moment to return; a +listing that needs one meanwhile answers EIO rather than waiting. + ``` program 9ns parent in new userns │ |