superblock: Convert to zerocopy/endian-aware

Vastly simplify processing of superblock structs by
using the zerocopy derive traits and eliminate a
whole bunch of hacks/unsafe.

Also nice: Endian aware now.

For more niceness, add `test-log` to allow use of
the logging macros in test suites.

Signed-off-by: Ikey Doherty <[email protected]>

Author: ikeycode

Cargo.lock

@@ -11,6 +11,8 @@ members = [
 
 [workspace.dependencies]
 log = "0.4.21"
+test-log = "0.2.17"
 thiserror = "2.0.3"
 uuid = { version = "1.8.0", features = ["v8"] }
 zstd = "0.13.1"
+zerocopy = "0.8.0"

Cargo.toml

@@ -9,6 +9,8 @@ edition = "2021"
 uuid = { workspace = true, features = ["v8"] }
 thiserror.workspace = true
 log.workspace = true
+zerocopy = { workspace = true, features = ["derive", "std"] }
 
 [dev-dependencies]
-zstd.workspace = true
+test-log.workspace = true
+zstd.workspace = true

crates/superblock/Cargo.toml

@@ -8,45 +8,42 @@
 
 use crate::{Error, Kind, Superblock};
 use log;
-use std::{
-    io::{self, Read},
-    slice,
-};
+use std::
+    io::{self, Read}
+;
 use uuid::Uuid;
+use zerocopy::*;
 
 /// BTRFS superblock definition (as seen in the kernel)
 /// This is a PARTIAL representation that matches only the
 /// first 72 bytes, verifies the magic, and permits extraction
 /// of the UUID
-#[derive(Debug)]
+#[derive(FromBytes, Debug)]
 #[repr(C)]
 pub struct Btrfs {
     csum: [u8; 32],
     fsid: [u8; 16],
-    bytenr: u64,
-    flags: u64,
-    magic: u64,
-    generation: u64,
-    root: u64,
-    chunk_root: u64,
-    log_root: u64,
+    bytenr: U64<LittleEndian>,
+    flags: U64<LittleEndian>,
+    magic: U64<LittleEndian>,
+    generation: U64<LittleEndian>,
+    root: U64<LittleEndian>,
+    chunk_root: U64<LittleEndian>,
+    log_root: U64<LittleEndian>,
 }
 
 // Superblock starts at 65536 for btrfs.
 const START_POSITION: u64 = 0x10000;
 
 // "_BHRfS_M"
-const MAGIC: u64 = 0x4D5F53665248425F;
+const MAGIC: U64<LittleEndian> = U64::new(0x4D5F53665248425F);
 
 /// Attempt to decode the Superblock from the given read stream
 pub fn from_reader<R: Read>(reader: &mut R) -> Result<Btrfs, Error> {
-    const SIZE: usize = std::mem::size_of::<Btrfs>();
-    let mut data: Btrfs = unsafe { std::mem::zeroed() };
-    let data_sliced = unsafe { slice::from_raw_parts_mut(&mut data as *mut _ as *mut u8, SIZE) };
-
     // Drop unwanted bytes (Seek not possible with zstd streamed inputs)
     io::copy(&mut reader.by_ref().take(START_POSITION), &mut io::sink())?;
-    reader.read_exact(data_sliced)?;
+
+    let data = Btrfs::read_from_io(reader).map_err(|_| Error::InvalidSuperblock)?;
 
     if data.magic != MAGIC {
         Err(Error::InvalidMagic)
@@ -78,7 +75,7 @@ mod tests {
 
     use crate::{btrfs::from_reader, Superblock};
 
-    #[test]
+    #[test_log::test]
     fn test_basic() {
         let mut fi = fs::File::open("tests/btrfs.img.zst").expect("cannot open ext4 img");
         let mut stream = zstd::stream::Decoder::new(&mut fi).expect("Unable to decode stream");

crates/superblock/src/btrfs.rs

@@ -6,114 +6,109 @@
 
 use crate::{Error, Kind, Superblock};
 use log;
-use std::{
-    io::{self, Read},
-    slice,
-};
+use std::io::{self, Read};
 use uuid::Uuid;
+use zerocopy::*;
 
 /// EXT4 Superblock definition (as seen in the kernel)
-#[derive(Debug)]
+#[derive(Debug, FromBytes)]
 #[repr(C)]
 pub struct Ext4 {
-    inodes_count: u32,
-    block_counts_lo: u32,
-    r_blocks_count_lo: u32,
-    free_blocks_count_lo: u32,
-    free_inodes_count: u32,
-    first_data_block: u32,
-    log_block_size: u32,
-    log_cluster_size: u32,
-    blocks_per_group: u32,
-    clusters_per_group: u32,
-    inodes_per_group: u32,
-    m_time: u32,
-    w_time: u32,
-    mnt_count: u16,
-    max_mnt_count: u16,
-    magic: u16,
-    state: u16,
-    errors: u16,
-    minor_rev_level: u16,
-    lastcheck: u32,
-    checkinterval: u32,
-    creator_os: u32,
-    rev_level: u32,
-    def_resuid: u16,
-    def_resgid: u16,
-    first_ino: u32,
-    inode_size: u16,
-    block_group_nr: u16,
-    feature_compat: u32,
-    feature_incompat: u32,
-    feature_ro_compat: u32,
+    inodes_count: U32<LittleEndian>,
+    block_counts_lo: U32<LittleEndian>,
+    r_blocks_count_lo: U32<LittleEndian>,
+    free_blocks_count_lo: U32<LittleEndian>,
+    free_inodes_count: U32<LittleEndian>,
+    first_data_block: U32<LittleEndian>,
+    log_block_size: U32<LittleEndian>,
+    log_cluster_size: U32<LittleEndian>,
+    blocks_per_group: U32<LittleEndian>,
+    clusters_per_group: U32<LittleEndian>,
+    inodes_per_group: U32<LittleEndian>,
+    m_time: U32<LittleEndian>,
+    w_time: U32<LittleEndian>,
+    mnt_count: U16<LittleEndian>,
+    max_mnt_count: U16<LittleEndian>,
+    magic: U16<LittleEndian>,
+    state: U16<LittleEndian>,
+    errors: U16<LittleEndian>,
+    minor_rev_level: U16<LittleEndian>,
+    lastcheck: U32<LittleEndian>,
+    checkinterval: U32<LittleEndian>,
+    creator_os: U32<LittleEndian>,
+    rev_level: U32<LittleEndian>,
+    def_resuid: U16<LittleEndian>,
+    def_resgid: U16<LittleEndian>,
+    first_ino: U32<LittleEndian>,
+    inode_size: U16<LittleEndian>,
+    block_group_nr: U16<LittleEndian>,
+    feature_compat: U32<LittleEndian>,
+    feature_incompat: U32<LittleEndian>,
+    feature_ro_compat: U32<LittleEndian>,
     uuid: [u8; 16],
     volume_name: [u8; 16],
     last_mounted: [u8; 64],
-    algorithm_usage_bitmap: u32,
+    algorithm_usage_bitmap: U32<LittleEndian>,
     prealloc_blocks: u8,
     prealloc_dir_blocks: u8,
-    reserved_gdt_blocks: u16,
+    reserved_gdt_blocks: U16<LittleEndian>,
     journal_uuid: [u8; 16],
-    journal_inum: u32,
-    journal_dev: u32,
-    last_orphan: u32,
-    hash_seed: [u32; 4],
+    journal_inum: U32<LittleEndian>,
+    journal_dev: U32<LittleEndian>,
+    last_orphan: U32<LittleEndian>,
+    hash_seed: [U32<LittleEndian>; 4],
     def_hash_version: u8,
     jnl_backup_type: u8,
-    desc_size: u16,
-    default_mount_opts: u32,
-    first_meta_bg: u32,
-    mkfs_time: u32,
-    jnl_blocks: [u32; 17],
-    blocks_count_hi: u32,
-    free_blocks_count_hi: u32,
-    min_extra_isize: u16,
-    want_extra_isize: u16,
-    flags: u32,
-    raid_stride: u16,
-    mmp_update_interval: u16,
-    mmp_block: u64,
-    raid_stripe_width: u32,
+    desc_size: U16<LittleEndian>,
+    default_mount_opts: U32<LittleEndian>,
+    first_meta_bg: U32<LittleEndian>,
+    mkfs_time: U32<LittleEndian>,
+    jnl_blocks: [U32<LittleEndian>; 17],
+    blocks_count_hi: U32<LittleEndian>,
+    free_blocks_count_hi: U32<LittleEndian>,
+    min_extra_isize: U16<LittleEndian>,
+    want_extra_isize: U16<LittleEndian>,
+    flags: U32<LittleEndian>,
+    raid_stride: U16<LittleEndian>,
+    mmp_update_interval: U16<LittleEndian>,
+    mmp_block: U64<LittleEndian>,
+    raid_stripe_width: U32<LittleEndian>,
     log_groups_per_flex: u8,
     checksum_type: u8,
-    reserved_pad: u16,
-    kbytes_written: u64,
-    snapshot_inum: u32,
-    snapshot_id: u32,
-    snapshot_r_blocks_count: u64,
-    snapshot_list: u32,
-    error_count: u32,
-    first_error_time: u32,
-    first_error_inod: u32,
-    first_error_block: u64,
+    reserved_pad: U16<LittleEndian>,
+    kbytes_written: U64<LittleEndian>,
+    snapshot_inum: U32<LittleEndian>,
+    snapshot_id: U32<LittleEndian>,
+    snapshot_r_blocks_count: U64<LittleEndian>,
+    snapshot_list: U32<LittleEndian>,
+    error_count: U32<LittleEndian>,
+    first_error_time: U32<LittleEndian>,
+    first_error_inod: U32<LittleEndian>,
+    first_error_block: U64<LittleEndian>,
     first_error_func: [u8; 32],
-    first_error_line: u32,
-    last_error_time: u32,
-    last_error_inod: u32,
-    last_error_line: u32,
-    last_error_block: u64,
+    first_error_line: U32<LittleEndian>,
+    last_error_time: U32<LittleEndian>,
+    last_error_inod: U32<LittleEndian>,
+    last_error_line: U32<LittleEndian>,
+    last_error_block: U64<LittleEndian>,
     last_error_func: [u8; 32],
     mount_opts: [u8; 64],
-    usr_quota_inum: u32,
-    grp_quota_inum: u32,
-    overhead_clusters: u32,
-    reserved: [u32; 108],
-    checksum: u32,
+    usr_quota_inum: U32<LittleEndian>,
+    grp_quota_inum: U32<LittleEndian>,
+    overhead_clusters: U32<LittleEndian>,
+    reserved: [U32<LittleEndian>; 108],
+    checksum: U32<LittleEndian>,
 }
 
-const MAGIC: u16 = 0xEF53;
+const MAGIC: U16<LittleEndian> = U16::new(0xEF53);
 const START_POSITION: u64 = 1024;
 
 /// Attempt to decode the Superblock from the given read stream
 pub fn from_reader<R: Read>(reader: &mut R) -> Result<Ext4, Error> {
-    const SIZE: usize = std::mem::size_of::<Ext4>();
-    let mut data: Ext4 = unsafe { std::mem::zeroed() };
-    let data_sliced = unsafe { slice::from_raw_parts_mut(&mut data as *mut _ as *mut u8, SIZE) };
-
     // Drop unwanted bytes (Seek not possible with zstd streamed inputs)
     io::copy(&mut reader.by_ref().take(START_POSITION), &mut io::sink())?;
-    reader.read_exact(data_sliced)?;
+
+    let data = Ext4::read_from_io(reader).map_err(|_| Error::InvalidSuperblock)?;
 
     if data.magic != MAGIC {
         Err(Error::InvalidMagic)
@@ -150,7 +145,7 @@ mod tests {
 
     use crate::{ext4::from_reader, Superblock};
 
-    #[test]
+    #[test_log::test]
     fn test_basic() {
         let mut fi = fs::File::open("tests/ext4.img.zst").expect("cannot open ext4 img");
         let mut stream = zstd::stream::Decoder::new(&mut fi).expect("Unable to decode stream");