compose: Change /etc/default/useradd to use HOME=/var/home

For a long time I've resisted encoding "policy" into rpm-ostree
as much as possible.  Doing so makes it more distribution specific
for example.  That said, for `/var/home` there argument for doing
this in rpm-ostree is that we already make that symlink in our
hardcoded rootfs.  So we might as well do the other fixups for it.

coreos/fedora-coreos-config#18
https://pagure.io/workstation-ostree-config/pull-request/121
https://discussion.fedoraproject.org/t/adapting-user-home-in-etc-passwd/487/6
justjanne/powerline-go#94

rust/src/composepost.rs

@@ -17,11 +17,66 @@
  */
 
 use openat;
+use std::{io, fs};
+use std::io::{Write, BufRead};
+use std::path::Path;
 use failure::Fallible;
 
+// IMO should propose this at least in a "utils" bit of the openat crate;
+// Like 95% of the time I'm looking at errno (with files) it's for ENOENT,
+// and Rust has an elegant way to map that with Option<>.  Every other
+// error I usually just want to propagate back up.
+fn openat_optional<P, F>(d: &openat::Dir, p: P, f: F) -> io::Result<Option<fs::File>>
+    where P: openat::AsPath, F: FnOnce(&openat::Dir, P) -> io::Result<fs::File>
+{
+    match f(d, p) {
+        Ok(f) => Ok(Some(f)),
+        Err(e) => {
+            if e.kind() == io::ErrorKind::NotFound {
+                Ok(None)
+            } else {
+                Err(e)
+            }
+        }
+    }
+}
+
+// rpm-ostree uses /home → /var/home by default as generated by our
+// rootfs; we don't expect people to change this.  Let's be nice
+// and also fixup the $HOME entries generated by `useradd` so
+// that `~` shows up as expected in shells, etc.
+//
+// https://github.com/coreos/fedora-coreos-config/pull/18
+// https://pagure.io/workstation-ostree-config/pull-request/121
+// https://discussion.fedoraproject.org/t/adapting-user-home-in-etc-passwd/487/6
+// https://github.com/justjanne/powerline-go/issues/94
+fn postprocess_useradd(rootfs_dfd: &openat::Dir) -> Fallible<()>
+{
+    let path = Path::new("usr/etc/default/useradd");
+    if let Some(f) = openat_optional(rootfs_dfd, path, openat::Dir::open_file)? {
+        let mut f = io::BufReader::new(f);
+        let o = rootfs_dfd.new_unnamed_file(0644)?;
+        let mut bufw = io::BufWriter::new(&o);
+        for line in f.lines() {
+            let line = line?;
+            if !line.starts_with("HOME=") {
+                bufw.write(line.as_bytes())?;
+            } else {
+                bufw.write("HOME=/var/home".as_bytes())?;
+            }
+            bufw.write("\n".as_bytes())?;
+        }
+        bufw.flush()?;
+        rootfs_dfd.remove_file(path)?;
+        rootfs_dfd.link_file_at(&o, path)?;
+    }
+    Ok(())
+}
+
 // This function is called from rpmostree_postprocess_final(); think of
 // it as the bits of that function that we've chosen to implement in Rust.
-fn compose_postprocess_final(_rootfs_dfd: &openat::Dir) -> Fallible<()> {
+fn compose_postprocess_final(rootfs_dfd: &openat::Dir) -> Fallible<()> {
+    postprocess_useradd(rootfs_dfd)?;
     Ok(())
 }
 

tests/compose-tests/libbasic-test.sh

@@ -19,6 +19,11 @@ validate_passwd() {
 validate_passwd passwd
 validate_passwd group
 
+
+ostree --repo=${repobuild} cat ${treeref} /usr/etc/default/useradd > useradd.txt
+assert_file_has_content_literal useradd.txt HOME=/var/home
+echo "ok etc/default/useradd"
+
 for path in /usr/share/rpm /usr/lib/sysimage/rpm-ostree-base-db; do
     ostree --repo=${repobuild} ls -R ${treeref} ${path} > db.txt
     assert_file_has_content_literal db.txt /Packages