cubefs: add .czyx.C.Z.Y.X FUSE magic-prefix for Phase-3 'open by CZYX' (same inode as canonical path)

STARTUP-README.md

@@ -45,11 +45,18 @@ is real. Each must be reproduced live, not asserted.
    `fixed-durable-20260813`). Re-verified 2026-08-13: OS state written to
    `/cubefs/c200/...` survived a `systemctl restart cube-server cubefs`. **STATUS: VERIFIED.**
 3. **Phase 3 syscall surface** — "open by CZYX + flags": a record addressable
-   directly by coordinate, not path. **SHIPPED 2026-08-13**: `cube open <path>
-   <K.Z.Y.X> <tf>` and `cube seal ...` are now first-class CLI commands (were
-   REPL/script-only) in `cubesys/src/bin/cube.rs`; reachable in-process AND over
-   the durable daemon via `cubec --socket /run/cube/cube.sock 'open ...'`.
-   Verified: dispatch reaches the crypto/run layer. **STATUS: DONE.**
+   directly by coordinate, not path. **SHIPPED 2026-08-13**:
+   (a) `cube open <path> <K.Z.Y.X> <tf>` and `cube seal ...` are first-class CLI
+   commands in `cubesys/src/bin/cube.rs` (reachable in-process + over the durable
+   daemon). Verified: dispatch reaches the crypto/run layer.
+   (b) **`.czyx.C.Z.Y.X` FUSE magic-prefix (2026-08-13)** — `cubefs/src/path.rs`
+   `parse_dot_czyx` + `cubefs/src/fuse.rs::lookup` intercept: a path component
+   `.czyx.200.50.1.7` resolves to the SAME inode as the canonical
+   `/cubefs/c200/z050/y001/x007` and reads/writes the real record. This is the
+   Phase-3 "open by CZYX" at the filesystem level — the kernel addresses the
+   record by coordinate. LIVE VERIFIED: stat both spellings -> identical inode
+   3358720263; `cat .czyx.200.50.1.7` returns the record content. Unit tests in
+   `path.rs` cover full/partial/rejected forms. **STATUS: DONE.**
 4. **Boot substrate** — the VM brings up CUBELinux as a storage layer the rest of
    the OS reads/writes through. **DONE (systemd-managed, 2026-08-13)**: units
    `cube-os-state.service` (oneshot, writes boot manifest + machine identity +

cubefs/src/fuse.rs

@@ -143,6 +143,25 @@ impl<B: CubeBackend> CubeFuse<B> {
 
 impl<B: CubeBackend + 'static> Filesystem for CubeFuse<B> {
     fn lookup(&mut self, _req: &Request<'_>, parent: u64, name: &OsStr, reply: ReplyEntry) {
+        // Phase-3 "open by CZYX": a `.czyx.C.Z.Y.X` name resolves directly to
+        // the coordinate's inode, independent of the canonical `cC/zZ/yY/xX`
+        // spelling. The kernel then opens the record *by its coordinate*.
+        if let Some(s) = name.to_str() {
+            if let Some(axes) = path::parse_dot_czyx(s) {
+                let non_zero: Vec<u8> = axes.iter().take_while(|&&v| v != 0).copied().collect();
+                let p = path::render_path(&non_zero);
+                match self.fs.getattr(&p) {
+                    Ok(a) => {
+                        reply.entry(&TTL, &to_file_attr(&a), 0);
+                        return;
+                    }
+                    Err(e) => {
+                        reply.error(errno(&e));
+                        return;
+                    }
+                }
+            }
+        }
         match self
             .child_path(parent, name)
             .and_then(|p| self.fs.getattr(&p))

cubefs/src/path.rs

@@ -198,6 +198,40 @@ pub fn render_path(axes: &[u8]) -> String {
     s
 }
 
+/// Parse the `.czyx.C.Z.Y.X` magic-prefix form — the Phase-3 "open by CZYX"
+/// at the filesystem level. A single path component `.czyx.12.34.56.78`
+/// resolves to the coordinate `(12,34,56,78)` regardless of the normal
+/// `c012/z034/y056/x078` spelling, so the kernel opens the record *by its
+/// coordinate*, not by path. Partial forms (`.czyx.12`, `.czyx.12.34`) address
+/// the synthetic directory prefix (trailing axes default to 0).
+///
+/// Returns the four axis values (trailing axes 0 for partial forms).
+pub fn parse_dot_czyx(name: &str) -> Option<[u8; 4]> {
+    let parts: Vec<&str> = name.split('.').collect();
+    // expect ["", "czyx", C, (Z)?, (Y)?, (X)?]
+    if parts.len() < 3 || !parts[0].is_empty() || parts[1] != "czyx" {
+        return None;
+    }
+    let mut axes = [0u8; 4];
+    let mut n = 0usize;
+    for p in &parts[2..] {
+        if n >= 4 {
+            return None; // too many axes
+        }
+        let v: u32 = p.parse().ok()?;
+        // 0 is Null control space; >255 is out of the addressable range.
+        if v == 0 || v > 255 {
+            return None;
+        }
+        axes[n] = v as u8;
+        n += 1;
+    }
+    if n == 0 {
+        return None;
+    }
+    Some(axes)
+}
+
 /// Coordinate -> inode number.
 ///
 /// The inode IS the packed coordinate; see the crate docs for why no side
@@ -302,6 +336,33 @@ mod tests {
         assert!(ino_to_czyx(u64::from(u32::MAX) + 1).is_none());
     }
 
+    #[test]
+    fn dot_czyx_magic_prefix() {
+        // Full coordinate form resolves to (C,Z,Y,X).
+        assert_eq!(parse_dot_czyx(".czyx.12.34.56.78"), Some([12, 34, 56, 78]));
+        // Partial forms fill trailing axes with 0 (directory prefixes).
+        assert_eq!(parse_dot_czyx(".czyx.7"), Some([7, 0, 0, 0]));
+        assert_eq!(parse_dot_czyx(".czyx.1.2.3"), Some([1, 2, 3, 0]));
+        // Rejects malformed input and out-of-range / Null values.
+        assert_eq!(parse_dot_czyx("czyx.1.2.3.4"), None); // missing leading dot
+        assert_eq!(parse_dot_czyx(".czyx"), None); // no axes
+        assert_eq!(parse_dot_czyx(".czyx.0.1.2.3"), None); // Null axis 0
+        assert_eq!(parse_dot_czyx(".czyx.1.2.3.4.5"), None); // too many axes
+        assert_eq!(parse_dot_czyx(".czyx.256"), None); // out of range
+        assert_eq!(parse_dot_czyx(".czyx.abc"), None); // non-numeric
+    }
+
+    #[test]
+    fn dot_czyx_resolves_same_ino_as_canonical() {
+        // The magic prefix must map to the *same inode* as the canonical path,
+        // so the kernel opens the record by coordinate, not path.
+        let axes = parse_dot_czyx(".czyx.12.34.56.78").unwrap();
+        let c = Czyx::new(axes[0], axes[1], axes[2], axes[3]);
+        let canonical = parse_path("/c012/z034/y056/x078").unwrap().czyx().unwrap();
+        assert_eq!(c, canonical);
+        assert_eq!(czyx_to_ino(c), czyx_to_ino(canonical));
+    }
+
     /// Exhaustive proof of bijectivity over the full record space would be
     /// 255^4 = 4.2e9 iterations; we sample the boundaries plus a stride so the
     /// test stays fast but still covers every axis extreme.