feat(fs/mem): tarfs implementation

Author: fogti

Cargo.lock

@@ -326,6 +326,7 @@ simple-shell = { version = "0.0.1", optional = true }
 smallvec = { version = "1", features = ["const_new"] }
 take-static = "0.1"
 talc = { version = "5" }
+tar-no-std = { version = "0.4", features = ["alloc"] }
 thiserror = { version = "2", default-features = false }
 time = { version = "0.3", default-features = false }
 volatile = "0.6"

Cargo.toml

@@ -122,15 +122,6 @@ pub(crate) struct RamFileInner {
 	pub attr: FileAttr,
 }
 
-impl RamFileInner {
-	pub fn new(attr: FileAttr) -> Self {
-		Self {
-			data: Vec::new(),
-			attr,
-		}
-	}
-}
-
 pub struct RamFileInterface {
 	/// Position within the file
 	pos: Mutex<usize>,
@@ -354,6 +345,10 @@ impl VfsNode for RamFile {
 
 impl RamFile {
 	pub fn new(mode: AccessPermission) -> Self {
+		Self::new_with_data(Vec::new(), mode)
+	}
+
+	fn new_with_data(data: Vec<u8>, mode: AccessPermission) -> Self {
 		let microseconds = arch::kernel::systemtime::now_micros();
 		let t = timespec::from_usec(microseconds as i64);
 		let attr = FileAttr {
@@ -365,7 +360,7 @@ impl RamFile {
 		};
 
 		Self {
-			data: Arc::new(RwLock::new(RamFileInner::new(attr))),
+			data: Arc::new(RwLock::new(RamFileInner { data, attr })),
 		}
 	}
 }
@@ -464,6 +459,44 @@ impl MemDirectory {
 		}
 	}
 
+	pub fn try_from_image(image: &'static [u8]) -> io::Result<Self> {
+		let this = Self::new(AccessPermission::S_IRUSR);
+
+		let taref = tar_no_std::TarArchiveRef::new(image).map_err(|e| {
+			error!("[Hermit image] Tar file has invalid format: {e:?}");
+			Errno::Inval
+		})?;
+
+		for i in taref.entries() {
+			let filename = i.filename();
+			let filename = filename.as_str().map_err(|e| {
+				error!(
+					"[Hermit image] Tar entry has not supported filename (non UTF-8): {filename:?}; {e}",
+				);
+				Errno::Inval
+			})?;
+
+			let mode = i.posix_header().mode.to_flags().map_err(|e| {
+				error!(
+					"[Hermit image] Tar entry {filename:?} has invalid mode: {:?}; {e}",
+					i.posix_header().mode,
+				);
+				Errno::Inval
+			})?;
+			let mode = AccessPermission::from_bits(mode.bits() as u32).ok_or_else(|| {
+				error!("[Hermit image] Tar entry {filename:?} has invalid mode: {mode:?}");
+				Errno::Inval
+			})?;
+
+			this.traverse_create_file(filename, i.data(), mode)
+				.inspect_err(|e| {
+					error!("[Hermit image] Unable to write entry {filename:?}: {e}");
+				})?;
+		}
+
+		Ok(this)
+	}
+
 	async fn async_traverse_open(
 		&self,
 		path: &str,
@@ -693,11 +726,16 @@ impl VfsNode for MemDirectory {
 					return directory.traverse_create_file(rest, data, mode);
 				}
 
-				let file = RomFile::new(data, mode);
-				self.inner
-					.write()
-					.await
-					.insert(component.to_owned(), Box::new(file));
+				let file: Box<dyn VfsNode> = if mode.contains(AccessPermission::S_IWUSR)
+					|| mode.contains(AccessPermission::S_IWGRP)
+					|| mode.contains(AccessPermission::S_IWOTH)
+				{
+					Box::new(RamFile::new_with_data(data.to_vec(), mode))
+				} else {
+					Box::new(RomFile::new(data, mode))
+				};
+
+				self.inner.write().await.insert(component.to_owned(), file);
 				Ok(())
 			},
 			None,

src/fs/mem.rs

@@ -304,7 +304,46 @@ pub(crate) fn init() {
 	const VERSION: &str = env!("CARGO_PKG_VERSION");
 	const UTC_BUILT_TIME: &str = build_time::build_time_utc!();
 
-	let root_filesystem = Filesystem::new();
+	let mut root_filesystem = Filesystem::new();
+
+	// Handle optional Hermit Image specified in FDT.
+	if let Some(fdt) = crate::env::fdt() {
+		let mut tar_image: Option<&'static [u8]> = None;
+
+		// per FDT specification, /chosen always exists.
+		let chosen = fdt.find_node("/chosen").unwrap();
+		if let Some(fdt::node::NodeProperty {
+			value: image_reg, ..
+		}) = chosen.property("image_reg")
+		{
+			let cell_sizes = fdt.root().cell_sizes();
+			let split_point = cell_sizes.address_cells * 4;
+			let end_point = split_point + cell_sizes.size_cells * 4;
+			if image_reg.len() == end_point {
+				let (addr, len) = image_reg.split_at(split_point);
+				if addr.len() == size_of::<*const u8>() && len.len() == size_of::<usize>() {
+					let addr = usize::from_be_bytes(addr.try_into().unwrap());
+					let len = usize::from_be_bytes(len.try_into().unwrap());
+					info!("Hermit image at {addr:x} with length {len:x}");
+					// technically, the following is UB, because the kernel might be contained within...
+					tar_image = Some(unsafe {
+						slice::from_raw_parts(core::ptr::with_exposed_provenance::<u8>(addr), len)
+					});
+				} else {
+					error!(
+						"Hermit image supplied with invalid address range (#addr = {}, #len = {})",
+						addr.len(),
+						len.len(),
+					);
+				}
+			}
+		}
+
+		if let Some(tar_image) = tar_image {
+			root_filesystem.root =
+				MemDirectory::try_from_image(tar_image).expect("Unable to parse Hermit Image");
+		}
+	}
 
 	root_filesystem
 		.mkdir("/tmp", AccessPermission::from_bits(0o777).unwrap())