Exit if booted into a container image

This is part of coreos/fedora-coreos-tracker#1263

We don't yet have an official stance on how zincati and custom
container images interact.  Today, zincati just crash loops.
This changes things so that we exit (but still with an error) if we detect
the booted system is using a container image origin.

One nicer thing here is that the unit status is also updated, e.g.
`systemctl status zincati` will show:

`Status: "Automatic updates disabled; booted into container image ..."`

dist/systemd/system/zincati.service

@@ -21,6 +21,8 @@ Environment=ZINCATI_VERBOSITY="-v"
 Type=notify
 ExecStart=/usr/libexec/zincati agent ${ZINCATI_VERBOSITY}
 Restart=on-failure
+# This status signals a non-restartable condition
+RestartPreventExitStatus=7
 RestartSec=10s
 
 [Install]

src/main.rs

@@ -56,20 +56,27 @@ fn run() -> i32 {
     match cli_opts.run() {
         Ok(_) => libc::EXIT_SUCCESS,
         Err(e) => {
-            log_error_chain(e);
-            libc::EXIT_FAILURE
+            log_error_chain(&e);
+            if e.root_cause()
+                .downcast_ref::<crate::rpm_ostree::FatalError>()
+                .is_some()
+            {
+                7
+            } else {
+                libc::EXIT_FAILURE
+            }
         }
     }
 }
 
 /// Pretty-print a chain of errors, as a series of error-priority log messages.
-fn log_error_chain(err_chain: anyhow::Error) {
+fn log_error_chain(err_chain: &anyhow::Error) {
     let mut chain_iter = err_chain.chain();
     let top_err = match chain_iter.next() {
         Some(e) => e.to_string(),
         None => "(unspecified failure)".to_string(),
     };
-    log::error!("critical error: {}", top_err);
+    log::error!("error: {}", top_err);
     for err in chain_iter {
         log::error!(" -> {}", err);
     }

src/rpm_ostree/cli_status.rs

@@ -37,6 +37,18 @@ lazy_static::lazy_static! {
     )).unwrap();
 }
 
+/// An error which should not result in a retry/restart.
+#[derive(Debug, Clone)]
+pub struct FatalError(String);
+
+impl std::fmt::Display for FatalError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl std::error::Error for FatalError {}
+
 /// JSON output from `rpm-ostree status --json`
 #[derive(Clone, Debug, Deserialize)]
 pub struct StatusJson {
@@ -48,6 +60,7 @@ pub struct StatusJson {
 #[serde(rename_all = "kebab-case")]
 pub struct DeploymentJson {
     booted: bool,
+    container_image_reference: Option<String>,
     base_checksum: Option<String>,
     #[serde(rename = "base-commit-meta")]
     base_metadata: BaseCommitMetaJson,
@@ -62,7 +75,7 @@ pub struct DeploymentJson {
 #[derive(Clone, Debug, Deserialize)]
 struct BaseCommitMetaJson {
     #[serde(rename = "fedora-coreos.stream")]
-    stream: String,
+    stream: Option<String>,
 }
 
 impl DeploymentJson {
@@ -85,12 +98,21 @@ impl DeploymentJson {
 
 /// Parse the booted deployment from status object.
 pub fn parse_booted(status: &StatusJson) -> Result<Release> {
-    let json = booted_json(status)?;
-    Ok(json.into_release())
+    let status = booted_json(status)?;
+    if let Some(img) = status.container_image_reference.as_ref() {
+        let msg = format!("Automatic updates disabled; booted into container image {img}");
+        crate::utils::update_unit_status(&msg);
+        return Err(anyhow::Error::new(FatalError(msg)));
+    }
+    Ok(status.into_release())
 }
 
 fn fedora_coreos_stream_from_deployment(deploy: &DeploymentJson) -> Result<String> {
-    let stream = deploy.base_metadata.stream.as_str();
+    let stream = deploy
+        .base_metadata
+        .stream
+        .as_ref()
+        .ok_or_else(|| anyhow!("Missing `fedora-coreos.stream` in commit metadata"))?;
     ensure!(!stream.is_empty(), "empty stream value");
     Ok(stream.to_string())
 }

src/rpm_ostree/mod.rs

@@ -1,7 +1,7 @@
 mod cli_deploy;
 mod cli_finalize;
 mod cli_status;
-pub use cli_status::{invoke_cli_status, parse_booted, parse_booted_updates_stream};
+pub use cli_status::{invoke_cli_status, parse_booted, parse_booted_updates_stream, FatalError};
 
 mod actor;
 pub use actor::{