ic_memory/runtime/
layout.rs

1//! Read-only adapter for the documented ic-stable-structures 0.7.2 MGR V1
2//! layout. No ledger or payload reads. Keep the dependency pinned when changing
3//! this adapter; layout changes require a new review, not a fallback decoder.
4use super::RuntimeConstructionError;
5use crate::WASM_PAGE_SIZE_BYTES;
6use ic_stable_structures::Memory;
7
8pub(super) const IDS: usize = 255;
9pub(super) const BUCKETS: usize = 32_768;
10pub(super) const HEADER_BYTES: usize = 40 + IDS * 8;
11pub(super) const METADATA_BYTES: usize = HEADER_BYTES + BUCKETS;
12
13///
14/// MemoryManagerLayoutError
15///
16/// Invalid or unsupported persisted manager metadata. No writes are performed
17/// when reporting these failures. Memory implementations must obey [`Memory`].
18///
19
20#[derive(Clone, Copy, Debug, Eq, PartialEq, thiserror::Error)]
21#[non_exhaustive]
22pub enum MemoryManagerLayoutError {
23    /// This adapter supports the little-endian IC/current native layout only.
24    #[error("unsupported big-endian manager layout")]
25    UnsupportedByteOrder,
26    /// The persisted bucket size is zero.
27    #[error("persisted bucket size is zero")]
28    ZeroBucketSize,
29    /// Reserved header fields are not recognized by this adapter.
30    #[error("nonzero reserved manager header bytes")]
31    ReservedHeader,
32    /// The allocated count exceeds the finite bucket table.
33    #[error("allocated bucket count {count} exceeds 32768")]
34    BucketCount { count: u16 },
35    /// Allocated buckets must be a dense prefix and all later entries unused.
36    #[error("invalid bucket table entry at index {index}")]
37    BucketTable { index: u16 },
38    /// Virtual extent disagrees with the number of assigned buckets.
39    #[error("virtual extent and bucket count disagree for memory ID {id}")]
40    VirtualExtent { id: u8 },
41    /// Backing memory does not cover every assigned bucket.
42    #[error("physical extent {physical_pages} pages is below assigned end {required_pages}")]
43    TruncatedBacking {
44        physical_pages: u64,
45        required_pages: u64,
46    },
47    /// Backing size cannot be represented in bytes.
48    #[error("backing memory extent overflows bytes")]
49    ExtentOverflow,
50    /// A live manager's cached state differs from persisted metadata.
51    #[error("persisted manager metadata differs from runtime authority")]
52    RuntimeMismatch,
53}
54
55pub(super) struct Layout {
56    pub physical_pages: u64,
57    pub bucket_pages: u16,
58    pub allocated_buckets: u16,
59    pub pages: [u64; IDS],
60    pub buckets: [u16; IDS],
61}
62
63pub(super) fn read<M: Memory>(memory: &M) -> Result<Layout, RuntimeConstructionError> {
64    if cfg!(target_endian = "big") {
65        return Err(MemoryManagerLayoutError::UnsupportedByteOrder.into());
66    }
67    let physical_pages = memory.size();
68    physical_pages
69        .checked_mul(WASM_PAGE_SIZE_BYTES)
70        .ok_or(MemoryManagerLayoutError::ExtentOverflow)?;
71    // The caller handles empty memory. Even one page covers all metadata.
72    if physical_pages == 0 {
73        return Err(MemoryManagerLayoutError::TruncatedBacking {
74            physical_pages,
75            required_pages: 1,
76        }
77        .into());
78    }
79    let mut header = [0; HEADER_BYTES];
80    memory.read(0, &mut header);
81    let observed_magic = [header[0], header[1], header[2]];
82    if observed_magic != *b"MGR" {
83        return Err(RuntimeConstructionError::ForeignMemory { observed_magic });
84    }
85    if header[3] != 1 {
86        return Err(RuntimeConstructionError::UnsupportedMemoryManagerVersion {
87            observed: header[3],
88            supported: 1,
89        });
90    }
91    if header[8..40].iter().any(|byte| *byte != 0) {
92        return Err(MemoryManagerLayoutError::ReservedHeader.into());
93    }
94    let allocated_buckets = u16::from_le_bytes([header[4], header[5]]);
95    let bucket_pages = u16::from_le_bytes([header[6], header[7]]);
96    if bucket_pages == 0 {
97        return Err(MemoryManagerLayoutError::ZeroBucketSize.into());
98    }
99    if usize::from(allocated_buckets) > BUCKETS {
100        return Err(MemoryManagerLayoutError::BucketCount {
101            count: allocated_buckets,
102        }
103        .into());
104    }
105    let required_pages = 1 + u64::from(allocated_buckets) * u64::from(bucket_pages);
106    if physical_pages < required_pages {
107        return Err(MemoryManagerLayoutError::TruncatedBacking {
108            physical_pages,
109            required_pages,
110        }
111        .into());
112    }
113    // Fixed allocation and read bound, independent of physical size/history.
114    let mut table = vec![0; BUCKETS];
115    memory.read(HEADER_BYTES as u64, &mut table);
116    let mut buckets = [0_u16; IDS];
117    for (index, id) in (0_u16..32_768).zip(table) {
118        if (index < allocated_buckets) != (id != 255) {
119            return Err(MemoryManagerLayoutError::BucketTable { index }.into());
120        }
121        if id != 255 {
122            buckets[usize::from(id)] += 1;
123        }
124    }
125    let mut pages = [0; IDS];
126    for (id, value) in (0_u8..255).zip(&mut pages) {
127        let offset = 40 + usize::from(id) * 8;
128        *value = u64::from_le_bytes(header[offset..offset + 8].try_into().expect("eight bytes"));
129        if value.div_ceil(u64::from(bucket_pages)) != u64::from(buckets[usize::from(id)]) {
130            return Err(MemoryManagerLayoutError::VirtualExtent { id }.into());
131        }
132    }
133    Ok(Layout {
134        physical_pages,
135        bucket_pages,
136        allocated_buckets,
137        pages,
138        buckets,
139    })
140}
ic_memory/runtime/layout.rs

ic_memory/runtime/
layout.rs
