rsext4 0.3.1

A lightweight ext4 file system.
Documentation 
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use super::*;
use crate::{
    BLOCK_SIZE, bmalloc::InodeNumber, disknode::Ext4Inode, endian::DiskFormat,
    entries::Ext4DirEntryTail, error::Errno, superblock::Ext4Superblock,
};

fn metadata_csum_superblock() -> Ext4Superblock {
    let mut sb = Ext4Superblock::default();
    sb.s_magic = Ext4Superblock::EXT4_SUPER_MAGIC;
    sb.s_feature_ro_compat |= Ext4Superblock::EXT4_FEATURE_RO_COMPAT_METADATA_CSUM;
    sb.s_inode_size = Ext4Inode::LARGE_INODE_SIZE;
    sb.s_clusters_per_group = 8192;
    sb.s_inodes_per_group = 2048;
    sb.s_blocks_count_lo = 1024;
    sb.s_free_blocks_count_lo = 900;
    sb.s_free_inodes_count = 2000;
    sb.s_uuid = [
        0x5A, 0xC3, 0x11, 0x7E, 0x90, 0xAB, 0x4D, 0x2F, 0x10, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
        0x88,
    ];
    sb
}

fn sample_inode() -> Ext4Inode {
    let mut inode = Ext4Inode {
        i_mode: Ext4Inode::S_IFREG | 0o764,
        i_uid: 0x1234,
        i_size_lo: 0x5566_7788,
        i_atime: 100,
        i_ctime: 200,
        i_mtime: 300,
        i_dtime: 0,
        i_gid: 0x5678,
        i_links_count: 2,
        i_blocks_lo: 16,
        i_flags: Ext4Inode::EXT4_EXTENTS_FL,
        l_i_version: 7,
        i_generation: 0xCAFE_BABE,
        i_size_high: 1,
        l_i_blocks_high: 2,
        l_i_uid_high: 0x9ABC,
        l_i_gid_high: 0xDEF0,
        i_extra_isize: Ext4Inode::required_extra_isize(Ext4Inode::FIELD_END_I_PROJID),
        i_crtime: 400,
        i_projid: 123,
        ..Default::default()
    };
    inode.write_extend_header();
    inode
}

#[test]
fn superblock_checksum_round_trips_and_corruption_returns_euclean() {
    // Test idea: once a checksummed superblock is serialized, verification should accept
    // the stored value and reject a single-byte metadata mutation with EUCLEAN.
    let mut sb = metadata_csum_superblock();
    sb.update_checksum();

    let verified = sb.verify_superblock().unwrap();
    assert_eq!(verified.s_checksum, sb.s_checksum);

    let mut bytes = [0u8; Ext4Superblock::SUPERBLOCK_SIZE];
    sb.to_disk_bytes(&mut bytes);
    let stored = u32::from_le_bytes(
        bytes[Ext4Superblock::SUPERBLOCK_SIZE - 4..]
            .try_into()
            .unwrap(),
    );
    assert_eq!(stored, sb.s_checksum);

    let mut corrupted = sb;
    corrupted.s_free_blocks_count_lo ^= 1;
    let err = corrupted.verify_superblock().unwrap_err();
    assert_eq!(err.code, Errno::EUCLEAN);
}

#[test]
fn inode_checksum_is_split_and_persisted_to_disk() {
    // Test idea: inode checksum helpers must both compute the expected CRC32C value and
    // split it into the low/high on-disk checksum fields.
    let sb = metadata_csum_superblock();
    let inode_num = InodeNumber::new(42).unwrap();
    let generation = 0x1020_3040;
    let inode_size = Ext4Inode::LARGE_INODE_SIZE as usize;
    let mut inode = sample_inode();
    inode.i_generation = generation;

    ext4_update_inode_checksum(&sb, inode_num, generation, &mut inode, inode_size);

    let expected = ext4_inode_csum32(&sb, inode_num, generation, &inode, inode_size);
    assert_eq!(inode.l_i_checksum_lo, (expected & 0xFFFF) as u16);
    assert_eq!(inode.i_checksum_hi, ((expected >> 16) & 0xFFFF) as u16);

    let mut bytes = [0u8; Ext4Inode::LARGE_INODE_SIZE as usize];
    inode.to_disk_bytes(&mut bytes);
    assert_eq!(
        u16::from_le_bytes(bytes[124..126].try_into().unwrap()),
        inode.l_i_checksum_lo
    );
    assert_eq!(
        u16::from_le_bytes(bytes[130..132].try_into().unwrap()),
        inode.i_checksum_hi
    );
}

#[test]
fn dirblock_checksum_is_stored_and_detects_corruption() {
    // Test idea: directory block CRC must be written into the tail and verification must
    // fail after mutating any protected byte in the directory payload.
    let sb = metadata_csum_superblock();
    let ino = 11;
    let generation = 0x5566_7788;
    let mut block = [0u8; BLOCK_SIZE];
    let tail_offset = BLOCK_SIZE - Ext4DirEntryTail::TAIL_LEN as usize;

    block[..12].copy_from_slice(b"hello crc32c");
    Ext4DirEntryTail::new().to_disk_bytes(&mut block[tail_offset..tail_offset + 12]);

    update_ext4_dirblock_csum32(&sb, ino, generation, &mut block);

    let stored = u32::from_le_bytes(block[BLOCK_SIZE - 4..].try_into().unwrap());
    let expected = ext4_dirblock_csum32(&sb, ino, generation, &block[..tail_offset]);
    assert_eq!(stored, expected);
    assert!(verify_ext4_dirblock_checksum(&sb, ino, generation, &block));

    block[0] ^= 0x80;
    assert!(!verify_ext4_dirblock_checksum(&sb, ino, generation, &block));
}