Z erofs decompression

README.md

@@ -121,7 +121,7 @@ erofs-cli inspect -i http://example.com/images/system.erofs cat /etc/os-release
 ### TODO
 
 - [ ] Extended attributes
-- [ ] Compressed data (lz4, lzma, deflate)
+- [-] Compressed data (lz4, lzma, deflate)
 - [ ] Image building (`mkfs.erofs` equivalent)
 
 ## License

erofs/src/decomp/mod.rs

@@ -0,0 +1,36 @@
+//! Basic Z_EROFS decompression support.
+//!
+//! This roughly follows parts of the Linux kernel implementation
+//! (fs/erofs/zmap.c, zdata.c), but is not a 1:1 port.
+//!
+//! The idea is:
+//! 1. VLE index  maps logical clusters
+//! 2. pclusters - contain compressed data
+//! 3. decompression - handled via lz4/lzma/deflate (not implemented here yet)
+//!
+//! Some details are still incomplete.
+
+#[derive(Debug, Clone, Copy)]
+pub struct VLEIndex {
+    pub advise: u16,           // compression hints (di_advise)
+    pub cluster_offset: u16,   // offset within the decompressed cluster
+    pub block_addr: u32,       // physical block (only meaningful for HEAD entries)
+}
+
+impl VLEIndex {
+    /// Read a VLE index from raw bytes.
+    /// Expects at least 8 bytes (little-endian layout).
+    pub fn from_bytes(data: &[u8]) -> crate::Result<Self> {
+        if data.len() < 8 {
+            return Err(crate::Error::NotSupported(
+                "VLE index too short".into()
+            ));
+        }
+
+        Ok(Self {
+            advise: u16::from_le_bytes([data[0], data[1]]),
+            cluster_offset: u16::from_le_bytes([data[2], data[3]]),
+            block_addr: u32::from_le_bytes([data[4], data[5], data[6], data[7]]),
+        })
+    }
+}

erofs/src/filesystem.rs

@@ -125,6 +125,8 @@ impl EroFSCore {
                 Ok(BlockPlan::Direct { offset, size: len })
             }
             Layout::CompressedFull | Layout::CompressedCompact => {
+                // TODO: Implement VLE index parsing and pcluster decompression
+                // See: decomp module, kernel fs/erofs/zmap.c + zdata.c
                 Err(Error::NotSupported("compressed compact layout".to_string()))
             }
             Layout::ChunkBased => {

erofs/src/lib.rs

@@ -53,6 +53,7 @@ extern crate std;
 
 pub(crate) mod dirent;
 pub(crate) mod filesystem;
+pub(crate) mod decomp;
 
 pub mod r#async;
 pub mod backend;