lcpfs 2026.1.102

LCP File System - A ZFS-inspired copy-on-write filesystem for Rust
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88

// Copyright 2025 LunaOS Contributors
// SPDX-License-Identifier: Apache-2.0

//! # Reflink Engine (Quantum Copy)
//!
//! This module implements O(1) file copying through block pointer aliasing,
//! also known as "reflinks" or "copy-on-write clones".
//!
//! ## Overview
//!
//! Traditional file copies require reading and writing every byte. With
//! reflinks, LCPFS creates an instant clone by sharing block pointers
//! between the source and destination files.
//!
//! ## How It Works
//!
//! ```text
//! Before Reflink:
//!   Source blkptr[0] --> Block A (refcount=1)
//!   Source blkptr[1] --> Block B (refcount=1)
//!
//! After Reflink (instant!):
//!   Source blkptr[0] --> Block A (refcount=2) <-- Dest blkptr[0]
//!   Source blkptr[1] --> Block B (refcount=2) <-- Dest blkptr[1]
//! ```
//!
//! ## Copy-on-Write
//!
//! When either file is modified, LCPFS allocates new blocks only for the
//! changed data, preserving the original blocks for the other file.
//!
//! ## Usage
//!
//! ```rust,ignore
//! use lcpfs::lcpfs_reflink::ReflinkEngine;
//!
//! // Instant O(1) copy
//! ReflinkEngine::entangle(&src_dnode, &mut dest_dnode)?;
//! ```

use crate::dedup::dedup::DDT;
use crate::fscore::structs::{Blkptr, DnodePhys};

/// Reflink engine for O(1) file copies
pub struct ReflinkEngine;

impl ReflinkEngine {
    /// Performs an instantaneous "Quantum Copy" of a file.
    pub fn entangle(src_dnode: &DnodePhys, dest_dnode: &mut DnodePhys) -> Result<(), &'static str> {
        // crate::lcpfs_println!("[ QUANTUM] Initiating Entanglement (Reflink)...");

        // 1. Structural Compatibility Check
        if src_dnode.indirection_levels != dest_dnode.indirection_levels
            && dest_dnode.used_bytes > 0
        {
            return Err("Destination not empty");
        }

        // 2. Clone the Block Pointers (The Entanglement)
        dest_dnode.nblkptr = src_dnode.nblkptr;
        dest_dnode.indirection_levels = src_dnode.indirection_levels;
        dest_dnode.max_blkid = src_dnode.max_blkid;
        dest_dnode.used_bytes = src_dnode.used_bytes;

        for i in 0..3 {
            dest_dnode.blkptr[i] = src_dnode.blkptr[i];

            // 3. Increment Reference Counts (The Anchor)
            if !src_dnode.blkptr[i].is_hole() {
                Self::increment_ref_tree(&src_dnode.blkptr[i]);
            }
        }

        crate::lcpfs_println!("[ QUANTUM] Entanglement Complete. 0 bytes copied.");
        Ok(())
    }

    fn increment_ref_tree(bp: &Blkptr) {
        let dva = bp.dva[0];
        let mut ddt = DDT.lock();

        if let Some(entry) = ddt.table.values_mut().find(|e| e.dva == dva) {
            entry.ref_count += 1;
        } else {
            // New entry logic would go here
        }
    }
}