Add a composefs backend

Makefile

@@ -113,6 +113,7 @@ validate-rust:
 	cargo test --no-run
 	(cd crates/ostree-ext && cargo check --no-default-features)
 	(cd crates/lib && cargo check --no-default-features)
+	cargo check --features=composefs-backend
 	cargo clippy -- $(CLIPPY_CONFIG)
 	env RUSTDOCFLAGS='-D warnings' cargo doc --lib
 .PHONY: validate-rust

crates/etc-merge/src/lib.rs

@@ -20,7 +20,9 @@ use cap_std_ext::dirext::CapStdExtDirExt;
 use composefs::fsverity::{FsVerityHashValue, Sha256HashValue, Sha512HashValue};
 use composefs::generic_tree::{Directory, Inode, Leaf, LeafContent, Stat};
 use composefs::tree::ImageError;
-use rustix::fs::{AtFlags, Gid, Uid, XattrFlags, lgetxattr, llistxattr, lsetxattr, readlinkat};
+use rustix::fs::{
+    AtFlags, Gid, Uid, XattrFlags, lgetxattr, llistxattr, lsetxattr, readlinkat, symlinkat,
+};
 
 /// Metadata associated with a file, directory, or symlink entry.
 #[derive(Debug)]
@@ -627,9 +629,8 @@ fn merge_leaf(
         .context(format!("Deleting {file:?}"))?;
 
     if let Some(target) = symlink {
-        new_etc_fd
-            .symlink(target.as_ref(), &file)
-            .context(format!("Creating symlink {file:?}"))?;
+        // Using rustix's symlinkat here as we might have absolute symlinks which clash with ambient_authority
+        symlinkat(&**target, new_etc_fd, file).context(format!("Creating symlink {file:?}"))?;
     } else {
         current_etc_fd
             .copy(&file, new_etc_fd, &file)

crates/initramfs/src/lib.rs

@@ -112,8 +112,9 @@ pub fn mount_at_wrapper(
         .with_context(|| format!("Mounting at path {path:?}"))
 }
 
+/// Wrapper around [`rustix::fs::openat`]
 #[context("Opening dir {name:?}")]
-fn open_dir(dirfd: impl AsFd, name: impl AsRef<Path> + Debug) -> Result<OwnedFd> {
+pub fn open_dir(dirfd: impl AsFd, name: impl AsRef<Path> + Debug) -> Result<OwnedFd> {
     let res = openat(
         dirfd,
         name.as_ref(),

crates/kernel_cmdline/src/lib.rs

@@ -12,3 +12,8 @@
 
 pub mod bytes;
 pub mod utf8;
+
+/// This is used by dracut.
+pub const INITRD_ARG_PREFIX: &str = "rd.";
+/// The kernel argument for configuring the rootfs flags.
+pub const ROOTFLAGS: &str = "rootflags";

crates/lib/Cargo.toml

@@ -23,6 +23,7 @@ bootc-tmpfiles = { path = "../tmpfiles" }
 bootc-utils = { package = "bootc-internal-utils", path = "../utils", version = "0.0.0" }
 ostree-ext = { path = "../ostree-ext", features = ["bootc"] }
 etc-merge = { path = "../etc-merge" }
+bootc-initramfs-setup = { path = "../initramfs" }
 
 # Workspace dependencies
 anstream = { workspace = true }