tool: improve sd-boot generation display name

Leverage the bootspec `label` field in its intended way. The VERSION_ID
of the os-release in the stub now only contains the generation number
and the build time. This makes a correct PRETTY_NAME entirely dependent
on correct information in the bootspec `label` field.

rust/tool/src/generation.rs

@@ -80,22 +80,12 @@ impl Generation {
     ///
     /// This is currently implemented by poking around the filesystem to find the necessary data.
     /// Ideally, the needed data should be included in the bootspec.
-    pub fn describe(&self) -> Result<String> {
+    pub fn describe(&self) -> String {
-        let toplevel = &self.spec.bootspec.toplevel.0;
-
-        let nixos_version = fs::read_to_string(toplevel.join("nixos-version"))
-            .unwrap_or_else(|_| String::from("Unknown"));
-        let kernel_version =
-            read_kernel_version(toplevel).context("Failed to read kernel version.")?;
         let build_time = self
             .build_time
             .map(|x| x.to_string())
             .unwrap_or_else(|| String::from("Unknown"));
-
+        format!("Generation {}, Built on {}", self.version, build_time)
-        Ok(format!(
-            "Generation {} NixOS {}, Linux Kernel {}, Built on {}",
-            self.version, nixos_version, kernel_version, build_time
-        ))
     }
 }
 
@@ -105,25 +95,6 @@ impl fmt::Display for Generation {
     }
 }
 
-/// Read the kernel version from the name of a directory inside the toplevel directory.
-///
-/// The path looks something like this: $toplevel/kernel-modules/lib/modules/6.1.1
-fn read_kernel_version(toplevel: &Path) -> Result<String> {
-    let path = fs::read_dir(toplevel.join("kernel-modules/lib/modules"))?
-        .into_iter()
-        .next()
-        .transpose()?
-        .map(|x| x.path())
-        .with_context(|| format!("Failed to read directory {:?}.", toplevel))?;
-
-    let file_name = path
-        .file_name()
-        .and_then(|x| x.to_str())
-        .context("Failed to convert path to filename string.")?;
-
-    Ok(String::from(file_name))
-}
-
 fn read_build_time(path: &Path) -> Result<Date> {
     let build_time = time::OffsetDateTime::from_unix_timestamp(fs::metadata(path)?.mtime())?.date();
     Ok(build_time)

rust/tool/src/os_release.rs

@@ -27,12 +27,7 @@ impl OsRelease {
         // it is fine to use a dummy value.
         map.insert("ID".into(), String::from("lanza"));
         map.insert("PRETTY_NAME".into(), generation.spec.bootspec.label.clone());
-        map.insert(
+        map.insert("VERSION_ID".into(), generation.describe());
-            "VERSION_ID".into(),
-            generation
-                .describe()
-                .context("Failed to describe generation.")?,
-        );
 
         Ok(Self(map))
     }

rust/tool/tests/os_release.rs

@@ -30,7 +30,7 @@ fn generate_expected_os_release() -> Result<()> {
     let expected = expect![[r#"
         ID=lanza
         PRETTY_NAME=LanzaOS
-        VERSION_ID=Generation 1 NixOS 23.05, Linux Kernel 6.1.1, Built on 1970-01-01
+        VERSION_ID=Generation 1, Built on 1970-01-01
     "#]];
 
     expected.assert_eq(&String::from_utf8(os_release_section)?);