Write write write your boat

Cargo.toml

@@ -22,6 +22,7 @@ anyhow = "1"
 bitflags = "1"
 byteorder = "1"
 crc = "1"
+derivative = "2.1.1"
 positioned-io = "0.2"
 thiserror = "1"
 

shell.nix

@@ -0,0 +1,12 @@
+with import <nixpkgs> {};
+stdenv.mkDerivation rec {
+  name = "env";
+  env = buildEnv { name = name; paths = buildInputs; };
+  buildInputs = [
+    fuse
+    #fuse3
+    #fuse-common
+    rustup
+    pkg-config
+  ];
+}

src/block_groups.rs

@@ -17,6 +17,149 @@ struct Entry {
     max_inode_number: u32,
 }
 
+#[derive(Debug)]
+pub struct BlockGroup {
+    bg_block_bitmap_lo: u32,      /* Blocks bitmap block */
+    bg_inode_bitmap_lo: u32,      /* Inodes bitmap block */
+    bg_inode_table_lo: u32,       /* Inodes table block */
+    bg_free_blocks_count_lo: u16, /* Free blocks count */
+    bg_free_inodes_count_lo: u16, /* Free inodes count */
+    bg_used_dirs_count_lo: u16,   /* Directories count */
+    bg_flags: u16,                /* EXT4_BG_flags (INODE_UNINIT, etc) */
+    bg_exclude_bitmap_lo: u32,    /* Exclude bitmap for snapshots */
+    bg_block_bitmap_csum_lo: u16, /* crc32c(s_uuid+grp_num+bbitmap) LE */
+    bg_inode_bitmap_csum_lo: u16, /* crc32c(s_uuid+grp_num+ibitmap) LE */
+    bg_itable_unused_lo: u16,     /* Unused inodes count */
+    bg_checksum: u16,             /* crc16(sb_uuid+group+desc) */
+    bg_block_bitmap_hi: u32,      /* Blocks bitmap block MSB */
+    bg_inode_bitmap_hi: u32,      /* Inodes bitmap block MSB */
+    bg_inode_table_hi: u32,       /* Inodes table block MSB */
+    bg_free_blocks_count_hi: u16, /* Free blocks count MSB */
+    bg_free_inodes_count_hi: u16, /* Free inodes count MSB */
+    bg_used_dirs_count_hi: u16,   /* Directories count MSB */
+    bg_itable_unused_hi: u16,     /* Unused inodes count MSB */
+    bg_exclude_bitmap_hi: u32,    /* Exclude bitmap block MSB */
+    bg_block_bitmap_csum_hi: u16, /* crc32c(s_uuid+grp_num+bbitmap) BE */
+    bg_inode_bitmap_csum_hi: u16, /* crc32c(s_uuid+grp_num+ibitmap) BE */
+    bg_reserved: u32,             /* Padding to 64 bytes */
+}
+
+impl BlockGroup {
+    pub fn new(buffer: Vec<u8>, s_desc_size: u16) -> Result<BlockGroup, Error> {
+        let mut inner = io::Cursor::new(buffer);
+
+        let bg_block_bitmap_lo = inner.read_u32::<LittleEndian>()?; /* Blocks bitmap block */
+        let bg_inode_bitmap_lo = inner.read_u32::<LittleEndian>()?; /* Inodes bitmap block */
+        let bg_inode_table_lo = inner.read_u32::<LittleEndian>()?; /* Inodes table block */
+        let bg_free_blocks_count_lo = inner.read_u16::<LittleEndian>()?; /* Free blocks count */
+        let bg_free_inodes_count_lo = inner.read_u16::<LittleEndian>()?; /* Free inodes count */
+        let bg_used_dirs_count_lo = inner.read_u16::<LittleEndian>()?; /* Directories count */
+        let bg_flags = inner.read_u16::<LittleEndian>()?; /* EXT4_BG_flags (INODE_UNINIT, etc) */
+        let bg_exclude_bitmap_lo = inner.read_u32::<LittleEndian>()?; /* Exclude bitmap for snapshots */
+        let bg_block_bitmap_csum_lo = inner.read_u16::<LittleEndian>()?; /* crc32c(s_uuid+grp_num+bbitmap) LE */
+        let bg_inode_bitmap_csum_lo = inner.read_u16::<LittleEndian>()?; /* crc32c(s_uuid+grp_num+ibitmap) LE */
+        let bg_itable_unused_lo = inner.read_u16::<LittleEndian>()?; /* Unused inodes count */
+        let bg_checksum = inner.read_u16::<LittleEndian>()?; /* crc16(sb_uuid+group+desc) */
+
+        // In ext2, ext3, and ext4 (when the 64bit feature is not enabled),
+        // the block group descriptor was only 32 bytes long and therefore ends at bg_checksum.
+        // On an ext4 filesystem with the 64bit feature enabled, the block group descriptor expands
+        // to at least the 64 bytes described below; the size is stored in the superblock.
+
+        let bg_block_bitmap_hi = if s_desc_size > 32 {
+            inner.read_u32::<LittleEndian>()?
+        } else {
+            0
+        };
+        let bg_inode_bitmap_hi = if s_desc_size > 32 {
+            inner.read_u32::<LittleEndian>()?
+        } else {
+            0
+        };
+        let bg_inode_table_hi = if s_desc_size > 32 {
+            inner.read_u32::<LittleEndian>()?
+        } else {
+            0
+        };
+
+        let bg_free_blocks_count_hi = if s_desc_size > 32 {
+            inner.read_u16::<LittleEndian>()?
+        } else {
+            0
+        };
+
+        let bg_free_inodes_count_hi = if s_desc_size > 32 {
+            inner.read_u16::<LittleEndian>()?
+        } else {
+            0
+        };
+
+        /* Directories count MSB */
+        let bg_used_dirs_count_hi = if s_desc_size > 32 {
+            inner.read_u16::<LittleEndian>()?
+        } else {
+            0
+        };
+        /* Unused inodes count MSB */
+        let bg_itable_unused_hi = if s_desc_size > 32 {
+            inner.read_u16::<LittleEndian>()?
+        } else {
+            0
+        };
+        /* Exclude bitmap block MSB */
+        let bg_exclude_bitmap_hi = if s_desc_size > 32 {
+            inner.read_u32::<LittleEndian>()?
+        } else {
+            0
+        };
+        /* crc32c(s_uuid+grp_num+bbitmap) BE */
+        let bg_block_bitmap_csum_hi = if s_desc_size > 32 {
+            inner.read_u16::<LittleEndian>()?
+        } else {
+            0
+        };
+        /* crc32c(s_uuid+grp_num+ibitmap) BE */
+        let bg_inode_bitmap_csum_hi = if s_desc_size > 32 {
+            inner.read_u16::<LittleEndian>()?
+        } else {
+            0
+        };
+
+        /* Padding to 64 bytes */
+        let bg_reserved = if s_desc_size > 32 {
+            inner.read_u32::<LittleEndian>()?
+        } else {
+            0
+        };
+
+        Ok(BlockGroup {
+            bg_block_bitmap_lo,
+            bg_inode_bitmap_lo,
+            bg_inode_table_lo,
+            bg_free_blocks_count_lo,
+            bg_free_inodes_count_lo,
+            bg_used_dirs_count_lo,
+            bg_flags,
+            bg_exclude_bitmap_lo,
+            bg_block_bitmap_csum_lo,
+            bg_inode_bitmap_csum_lo,
+            bg_itable_unused_lo,
+            bg_checksum,
+            bg_block_bitmap_hi,
+            bg_inode_bitmap_hi,
+            bg_inode_table_hi,
+            bg_free_blocks_count_hi,
+            bg_free_inodes_count_hi,
+            bg_used_dirs_count_hi,
+            bg_itable_unused_hi,
+            bg_exclude_bitmap_hi,
+            bg_block_bitmap_csum_hi,
+            bg_inode_bitmap_csum_hi,
+            bg_reserved,
+        })
+    }
+}
+
 #[derive(Debug)]
 pub struct BlockGroups {
     groups: Vec<Entry>,
@@ -42,78 +185,28 @@ impl BlockGroups {
         let mut groups = Vec::with_capacity(blocks_count);
 
         for block in 0..blocks_count {
-            //            let bg_block_bitmap_lo =
-            inner.read_u32::<LittleEndian>()?; /* Blocks bitmap block */
-            //            let bg_inode_bitmap_lo =
-            inner.read_u32::<LittleEndian>()?; /* Inodes bitmap block */
-            let bg_inode_table_lo = inner.read_u32::<LittleEndian>()?; /* Inodes table block */
-            //            let bg_free_blocks_count_lo =
-            inner.read_u16::<LittleEndian>()?; /* Free blocks count */
-            let bg_free_inodes_count_lo = inner.read_u16::<LittleEndian>()?; /* Free inodes count */
-            //            let bg_used_dirs_count_lo =
-            inner.read_u16::<LittleEndian>()?; /* Directories count */
-            let bg_flags = inner.read_u16::<LittleEndian>()?; /* EXT4_BG_flags (INODE_UNINIT, etc) */
-            //            let bg_exclude_bitmap_lo =
-            inner.read_u32::<LittleEndian>()?; /* Exclude bitmap for snapshots */
-            //            let bg_block_bitmap_csum_lo =
-            inner.read_u16::<LittleEndian>()?; /* crc32c(s_uuid+grp_num+bbitmap) LE */
-            //            let bg_inode_bitmap_csum_lo =
-            inner.read_u16::<LittleEndian>()?; /* crc32c(s_uuid+grp_num+ibitmap) LE */
-            //            let bg_itable_unused_lo =
-            inner.read_u16::<LittleEndian>()?; /* Unused inodes count */
-            //            let bg_checksum =
-            inner.read_u16::<LittleEndian>()?; /* crc16(sb_uuid+group+desc) */
-
-            //            let bg_block_bitmap_hi =
-            if s_desc_size < 4 {
-                None
-            } else {
-                Some(inner.read_u32::<LittleEndian>()?) /* Blocks bitmap block MSB */
-            };
-            //            let bg_inode_bitmap_hi =
-            if s_desc_size < 4 + 4 {
-                None
-            } else {
-                Some(inner.read_u32::<LittleEndian>()?) /* Inodes bitmap block MSB */
-            };
-            let bg_inode_table_hi = if s_desc_size < 4 + 4 + 4 {
-                None
-            } else {
-                Some(inner.read_u32::<LittleEndian>()?) /* Inodes table block MSB */
-            };
-            //            let bg_free_blocks_count_hi =
-            if s_desc_size < 4 + 4 + 4 + 2 {
-                None
+            // let mut entire_blockgroup = [0u8; s_desc_size];
+            let bufsize = if s_desc_size == 0 {
+                32
             } else {
-                Some(inner.read_u16::<LittleEndian>()?) /* Free blocks count MSB */
-            };
-            let bg_free_inodes_count_hi = if s_desc_size < 4 + 4 + 4 + 2 + 2 {
-                None
-            } else {
-                Some(inner.read_u16::<LittleEndian>()?) /* Free inodes count MSB */
+                s_desc_size.into()
             };
+            let mut entire_blockgroup = vec![0u8; bufsize];
+            inner.read_exact(&mut entire_blockgroup)?;
+            let blockgroup = BlockGroup::new(entire_blockgroup, s_desc_size)?;
 
-            //          let bg_used_dirs_count_hi =
-            //              inner.read_u16::<LittleEndian>()?; /* Directories count MSB */
-            //          let bg_itable_unused_hi =
-            //              inner.read_u16::<LittleEndian>()?; /* Unused inodes count MSB */
-            //          let bg_exclude_bitmap_hi =
-            //              inner.read_u32::<LittleEndian>()?; /* Exclude bitmap block MSB */
-            //          let bg_block_bitmap_csum_hi =
-            //              inner.read_u16::<LittleEndian>()?; /* crc32c(s_uuid+grp_num+bbitmap) BE */
-            //          let bg_inode_bitmap_csum_hi =
-            //              inner.read_u16::<LittleEndian>()?; /* crc32c(s_uuid+grp_num+ibitmap) BE */
-            if s_desc_size > 16 + 32 {
-                inner.seek(io::SeekFrom::Current(i64::from(s_desc_size - 32 - 16)))?;
-            }
+            // AA TODO What was this about?
+            // if s_desc_size > 16 + 32 {
+            //     inner.seek(io::SeekFrom::Current(i64::from(s_desc_size - 32 - 16)))?;
+            // }
 
-            let inode_table_block =
-                u64::from(bg_inode_table_lo) | ((u64::from(bg_inode_table_hi.unwrap_or(0))) << 32);
-            let free_inodes_count = u32::from(bg_free_inodes_count_lo)
-                | ((u32::from(bg_free_inodes_count_hi.unwrap_or(0))) << 16);
+            let inode_table_block = u64::from(blockgroup.bg_inode_table_lo)
+                | ((u64::from(blockgroup.bg_inode_table_hi)) << 32);
+            let free_inodes_count = u32::from(blockgroup.bg_free_inodes_count_lo)
+                | ((u32::from(blockgroup.bg_free_inodes_count_hi)) << 16);
 
-            let unallocated = bg_flags & EXT4_BLOCK_GROUP_INODES_UNUSED != 0
-                || bg_flags & EXT4_BLOCK_GROUP_BLOCKS_UNUSED != 0;
+            let unallocated = blockgroup.bg_flags & EXT4_BLOCK_GROUP_INODES_UNUSED != 0
+                || blockgroup.bg_flags & EXT4_BLOCK_GROUP_BLOCKS_UNUSED != 0;
 
             if free_inodes_count > s_inodes_per_group {
                 return Err(crate::parse_error(format!(