rust/treefile: Support creating client from /etc dropins

Add support for creating a client treefile based on the dropins in
`/etc/rpm-ostree/origin.d`. This will currently be used only by the
container flow, but could eventually also end up being used client-side
as discussed in coreos#2326.

rust/src/lib.rs

@@ -392,6 +392,7 @@ pub mod ffi {
             workdir: i32,
         ) -> Result<Box<Treefile>>;
         fn treefile_new_client(filename: &str, basearch: &str) -> Result<Box<Treefile>>;
+        fn treefile_new_client_from_etc(basearch: &str) -> Result<Box<Treefile>>;
 
         fn get_workdir(&self) -> i32;
         fn get_passwd_fd(&mut self) -> i32;

rust/src/treefile.rs

@@ -28,11 +28,11 @@ use ostree_ext::{glib, ostree};
 use serde_derive::{Deserialize, Serialize};
 use std::collections::btree_map::Entry;
 use std::collections::{BTreeMap, HashMap, HashSet};
-use std::fs::File;
+use std::fs::{read_dir, File};
 use std::io::prelude::*;
 use std::os::unix::fs::{MetadataExt, PermissionsExt};
 use std::os::unix::io::{AsRawFd, RawFd};
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::pin::Pin;
 use std::{collections, fs, io};
 use tracing::{event, instrument, Level};
@@ -46,6 +46,9 @@ const INCLUDE_MAXDEPTH: u32 = 50;
 /// it's intended to be informative.
 const COMPOSE_JSON_PATH: &str = "usr/share/rpm-ostree/treefile.json";
 
+/// Path to client-side treefiles.
+const CLIENT_TREEFILES_DIR: &str = "/etc/rpm-ostree/origin.d";
+
 /// This struct holds file descriptors for any external files/data referenced by
 /// a TreeComposeConfig.
 #[derive(Debug, Default)]
@@ -1021,6 +1024,14 @@ impl TreefileExternals {
         }
         Ok(())
     }
+
+    fn assert_nonempty(&self) {
+        // can't use the Default trick here because we can't auto-derive Eq because of `File`
+        assert!(self.postprocess_script.is_none());
+        assert!(self.add_files.is_empty());
+        assert!(self.passwd.is_none());
+        assert!(self.group.is_none());
+    }
 }
 
 /// For increased readability in YAML/JSON, we support whitespace in individual
@@ -2260,3 +2271,37 @@ pub(crate) fn treefile_new_client(filename: &str, basearch: &str) -> CxxResult<B
     r.error_if_base()?;
     Ok(r)
 }
+
+fn iter_etc_treefiles() -> Result<impl Iterator<Item = Result<PathBuf>>> {
+    Ok(read_dir(CLIENT_TREEFILES_DIR)?.filter_map(|res| match res {
+        Ok(e) => {
+            let path = e.path();
+            if let Some(ext) = path.extension() {
+                if ext == "yaml" {
+                    return Some(anyhow::Result::Ok(path));
+                }
+            }
+            None
+        }
+        Err(err) => Some(Err(anyhow::Error::msg(err))),
+    }))
+}
+
+/// Create a new client treefile using the treefile dropins in /etc/rpm-ostree/origin.d/.
+pub(crate) fn treefile_new_client_from_etc(basearch: &str) -> CxxResult<Box<Treefile>> {
+    let basearch = opt_string(basearch);
+    let mut cfg = TreeComposeConfig::default();
+    let mut tfs = iter_etc_treefiles()?.collect::<Result<Vec<PathBuf>>>()?;
+    tfs.sort(); // sort because order matters; later treefiles override earlier ones
+    for tf in tfs {
+        let new_cfg = treefile_parse_and_process(tf, basearch)?;
+        new_cfg.config.base.error_if_nonempty()?;
+        new_cfg.externals.assert_nonempty();
+        let mut new_cfg = new_cfg.config;
+        treefile_merge(&mut new_cfg, &mut cfg);
+        cfg = new_cfg;
+    }
+    let r = Treefile::new_from_config(cfg, None)?;
+    r.error_if_base()?;
+    Ok(Box::new(r))
+}