# `gno.land/p/moul/x/plan9/synfs/v0`
**A synthetic, read-only file server whose contents are computed at read time.**
This is the package that makes the rest of the suite adoptable.
```go
import synfs "gno.land/p/moul/x/plan9/synfs/v0"
t := synfs.New("dev", "sys", func() int64 { return runtime.ChainHeight() })
t.Root().
Add("sysname", func() string { return runtime.ChainID() }).
Add("height", func() string { return strconv.FormatInt(runtime.ChainHeight(), 10) })
```
In Plan 9 a device is not storage, it is code behind a name: reading `/dev/time`
runs a function. A realm that wants to publish its state as a browsable tree
does the same thing here, in a few lines, and gets `ls`, `cat`, `stat` and
mountability for free.
**Read-only by construction.** The tree implements `ninep.File` and not
`ninep.Mutable`, so every method is free of side effects and the tree is safe to
hand to a namespace owned by somebody else. That is the property the whole
cross-realm mount story rests on.
Two details worth knowing:
- **A synthetic file pins `Qid.Version` at 0 forever.** Its contents can change
on every block, so a version would be a lie; a client that needs change
detection should read the file.
- **`AddRange` serves the 9P read window itself**, for a file with no natural
end. `/dev/zero` uses it: an unbounded read returns nothing rather than an
endless value, which is what stops `cat /dev/zero` from being a denial of
service.
**Live demo:** [`r/moul/x/plan9/dev`](../../../../../r/moul/x/plan9/dev/v0)
publishes the chain itself as a device tree. Design and analysis:
[moul/gno-contracts#136](https://github.com/moul/gno-contracts/issues/136).
---
**Not affiliated with Plan 9.** Plan 9 from Bell Labs is the work of the
Computing Science Research Center at Bell Labs; the name and the marks are
theirs, and the copyright is held by the [Plan 9 Foundation](https://p9f.org).
This package borrows the vocabulary and none of the code: it is an independent
homage, asking what that ecosystem's spirit looks like on a chain. Full
attribution: [NOTICE](../../../../../NOTICE.md).
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---
Part of **[moul/gno-contracts](https://github.com/moul/gno-contracts)** — moul's versioned gno.land contracts. See the repository for the full catalog, build/test tooling, and usage.
**Dependency graph:**
> 🧪 **Highly experimental — potentially vibe-coded.** Not audited; may break, change, or be removed at any time. Do not use with anything of value. Full disclaimer: [DISCLAIMER](https://github.com/moul/gno-contracts/blob/main/DISCLAIMER.md).
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Signatures reconstructed verbatim from vm/qfuncs — interface params keep their inline definitions.