lints: Check base image content

This is mainly a sanity check for people building custom base
images.

But it also unit tests our own reference content.

Signed-off-by: Colin Walters <[email protected]>

lib/src/lints.rs

@@ -3,15 +3,19 @@
 //! This module implements `bootc container lint`.
 
 use std::env::consts::ARCH;
+use std::os::unix::ffi::OsStrExt;
 
-use anyhow::{bail, ensure, Result};
+use anyhow::{bail, ensure, Context, Result};
 use cap_std::fs::Dir;
 use cap_std_ext::cap_std;
 use cap_std_ext::dirext::CapStdExtDirExt as _;
 use fn_error_context::context;
 
 use crate::utils::openat2_with_retry;
 
+/// Reference to embedded default baseimage content that should exist.
+const BASEIMAGE_REF: &str = "usr/share/doc/bootc/baseimage/base";
+
 /// check for the existence of the /var/run directory
 /// if it exists we need to check that it links to /run if not error
 /// if it does not exist error.
@@ -23,6 +27,7 @@ pub(crate) fn lint(root: &Dir) -> Result<()> {
         check_parse_kargs,
         check_usretc,
         check_utf8,
+        check_baseimage_root,
     ];
     for lint in lints {
         lint(&root)?;
@@ -116,6 +121,57 @@ fn check_utf8(dir: &Dir) -> Result<()> {
     Ok(())
 }
 
+/// Check for a few files and directories we expect in the base image.
+fn check_baseimage_root_norecurse(dir: &Dir) -> Result<()> {
+    // Check /sysroot
+    let meta = dir.symlink_metadata_optional("sysroot")?;
+    match meta {
+        Some(meta) if !meta.is_dir() => {
+            anyhow::bail!("Expected a directory for /sysroot")
+        }
+        None => anyhow::bail!("Missing /sysroot"),
+        _ => {}
+    }
+
+    // Check /ostree -> sysroot/ostree
+    let Some(meta) = dir.symlink_metadata_optional("ostree")? else {
+        anyhow::bail!("Missing ostree -> sysroot/ostree link")
+    };
+    if !meta.is_symlink() {
+        anyhow::bail!("/ostree should be a symlink");
+    }
+    let link = dir.read_link_contents("ostree")?;
+    let expected = "sysroot/ostree";
+    if link.as_os_str().as_bytes() != expected.as_bytes() {
+        anyhow::bail!("Expected /ostree -> {expected}, not {link:?}");
+    }
+
+    // Check the prepare-root config
+    let prepareroot_path = "usr/lib/ostree/prepare-root.conf";
+    let config_data = dir
+        .read_to_string(prepareroot_path)
+        .context(prepareroot_path)?;
+    let config = ostree_ext::glib::KeyFile::new();
+    config.load_from_data(&config_data, ostree_ext::glib::KeyFileFlags::empty())?;
+
+    if !ostree_ext::ostree_prepareroot::overlayfs_enabled_in_config(&config)? {
+        anyhow::bail!("{prepareroot_path} does not have composefs enabled")
+    }
+
+    Ok(())
+}
+
+/// Check ostree-related base image content.
+fn check_baseimage_root(dir: &Dir) -> Result<()> {
+    check_baseimage_root_norecurse(dir)?;
+    // If we have our own documentation with the expected root contents
+    // embedded, then check that too! Mostly just because recursion is fun.
+    if let Some(dir) = dir.open_dir_optional(BASEIMAGE_REF)? {
+        check_baseimage_root_norecurse(&dir)?;
+    }
+    Ok(())
+}
+
 #[cfg(test)]
 fn fixture() -> Result<cap_std_ext::cap_tempfile::TempDir> {
     let tempdir = cap_std_ext::cap_tempfile::tempdir(cap_std::ambient_authority())?;
@@ -257,3 +313,33 @@ fn test_non_utf8() {
     root.remove_file(badfile).unwrap(); // Get rid of the problem
     check_utf8(root).unwrap(); // Check it
 }
+
+#[test]
+fn test_baseimage_root() -> Result<()> {
+    use bootc_utils::CommandRunExt;
+    use cap_std_ext::cmdext::CapStdExtCommandExt;
+    use std::path::Path;
+
+    let td = fixture()?;
+
+    // An empty root should fail our test
+    assert!(check_baseimage_root(&td).is_err());
+
+    // Copy our reference base image content from the source dir
+    let manifest = std::env::var_os("CARGO_MANIFEST_PATH").unwrap();
+    let srcdir = Path::new(&manifest)
+        .parent()
+        .unwrap()
+        .join("../baseimage/base");
+    for ent in std::fs::read_dir(srcdir)? {
+        let ent = ent?;
+        std::process::Command::new("cp")
+            .cwd_dir(td.try_clone()?)
+            .arg("-pr")
+            .arg(ent.path())
+            .arg(".")
+            .run()?;
+    }
+    check_baseimage_root(&td).unwrap();
+    Ok(())
+}