# `gno.land/p/moul/x/plan9/memfs/v0`
**A RAM file server**: Plan 9's `ramfs`, in a realm's heap. The reference
implementation of [`ninep.File`](../../ninep/v0) and `ninep.Mutable`.
```go
import memfs "gno.land/p/moul/x/plan9/memfs/v0"
fs := memfs.New("g1...", runtime.ChainHeight())
fs.MkdirAll("/usr/glenda/bin", height)
fs.WriteFile("/tmp/greeting", "hello\n", height)
root := fs.Root() // a ninep.File, mountable into any namespace
```
Children live in an `avl.Tree`, so a directory listing is ordered by name and
therefore identical on every validating node. A map would make `Render` a
consensus bug.
**`Mutable` is in-realm only.** A non-crossing method runs in the *caller's*
frame, so a foreign realm calling `Create` or `Write` here would be mutating
objects it does not own. The read half is safe from anywhere, which is exactly
what makes a memfs tree mountable into somebody else's namespace: they get
reads, and only its owner gets writes.
**The clock is a parameter, not an import.** Every mutation takes the block
height from the caller rather than reading chain state itself, so the same tree
runs in a plain unit test.
9P behaviours reproduced rather than approximated:
- A directory reports `Length` 0, as 9P does.
- `Qid.Version` increments on every write, so a client holding a qid can tell
"same file, changed" from "different file" without reading it.
- Writing past the end extends the file with NUL bytes.
- `DMAPPEND` pins every write to the end, whatever offset was asked for.
- Removing a non-empty directory is refused.
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.