Improve parsing of ostree prepare-root config

Prep for further work.

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

Author: cgwalters

lib/src/lints.rs

@@ -6,14 +6,15 @@ use std::collections::BTreeSet;
 use std::env::consts::ARCH;
 use std::os::unix::ffi::OsStrExt;
 
-use anyhow::{Context, Result};
+use anyhow::Result;
 use camino::{Utf8Path, Utf8PathBuf};
 use cap_std::fs::Dir;
 use cap_std_ext::cap_std;
 use cap_std_ext::cap_std::fs::MetadataExt;
 use cap_std_ext::dirext::CapStdExtDirExt as _;
 use fn_error_context::context;
 use indoc::indoc;
+use ostree_ext::ostree_prepareroot;
 use serde::Serialize;
 
 /// Reference to embedded default baseimage content that should exist.
@@ -286,15 +287,8 @@ fn check_baseimage_root_norecurse(dir: &Dir) -> LintResult {
         return lint_err("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)? {
+    let config = ostree_prepareroot::require_config_from_root(dir)?;
+    if !ostree_prepareroot::overlayfs_enabled_in_config(&config)? {
         return lint_err("{prepareroot_path} does not have composefs enabled");
     }
 

ostree-ext/src/ostree_prepareroot.rs

@@ -3,11 +3,14 @@
 
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
+use std::io::Read;
 use std::str::FromStr;
 
 use anyhow::{Context, Result};
 use camino::Utf8Path;
+use cap_std_ext::dirext::CapStdExtDirExt;
 use glib::Cast;
+use ocidir::cap_std::fs::Dir;
 use ostree::prelude::FileExt;
 use ostree::{gio, glib};
 
@@ -37,6 +40,29 @@ pub(crate) fn load_config(root: &ostree::RepoFile) -> Result<Option<glib::KeyFil
     Ok(None)
 }
 
+/// Load the configuration from the target root.
+pub fn load_config_from_root(root: &Dir) -> Result<Option<glib::KeyFile>> {
+    for path in ["etc", "usr/lib"].into_iter().map(Utf8Path::new) {
+        let path = path.join(CONF_PATH);
+        let Some(mut f) = root.open_optional(&path)? else {
+            continue;
+        };
+        let mut contents = String::new();
+        f.read_to_string(&mut contents)?;
+        let kf = glib::KeyFile::new();
+        kf.load_from_data(&contents, glib::KeyFileFlags::NONE)
+            .with_context(|| format!("Parsing {path}"))?;
+        return Ok(Some(kf));
+    }
+    Ok(None)
+}
+
+/// Require the configuration in the target root.
+pub fn require_config_from_root(root: &Dir) -> Result<glib::KeyFile> {
+    load_config_from_root(root)?
+        .ok_or_else(|| anyhow::anyhow!("Failed to find {CONF_PATH} in /usr/lib or /etc"))
+}
+
 /// Query whether the target root has the `root.transient` key
 /// which sets up a transient overlayfs.
 pub(crate) fn overlayfs_root_enabled(root: &ostree::RepoFile) -> Result<bool> {