Merge pull request #161 from nix-community/safeguard-gc

tool: disable gc in the presence of malformed gens

rust/tool/Cargo.lock

@@ -473,6 +473,12 @@ dependencies = [
  "cxx-build",
 ]
 
+[[package]]
+name = "indoc"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f2cb48b81b1dc9f39676bf99f5499babfec7cd8fe14307f7b3d747208fb5690"
+
 [[package]]
 name = "instant"
 version = "0.1.12"
@@ -541,6 +547,7 @@ dependencies = [
  "fastrand",
  "filetime",
  "goblin",
+ "indoc",
  "log",
  "nix",
  "rand",

rust/tool/Cargo.toml

@@ -27,6 +27,7 @@ sha2 = "0.10.6"
 fastrand = "1.9.0"
 log = { version = "0.4.17", features = ["std"] }
 stderrlog = "0.5.4"
+indoc = "2.0.1"
 
 [dev-dependencies]
 assert_cmd = "2.0.11"

rust/tool/src/install.rs

@@ -18,6 +18,7 @@ use crate::systemd::SystemdVersion;
 use crate::utils::{file_hash, SecureTempDirExt};
 
 pub struct Installer {
+    enable_gc: bool,
     gc_roots: Roots,
     lanzaboote_stub: PathBuf,
     systemd: PathBuf,
@@ -43,6 +44,7 @@ impl Installer {
         gc_roots.extend(esp_paths.to_iter());
 
         Self {
+            enable_gc: true,
             gc_roots,
             lanzaboote_stub,
             systemd,
@@ -85,6 +87,7 @@ impl Installer {
 
         self.install_systemd_boot()?;
 
+        if self.enable_gc {
             log::info!("Collecting garbage...");
             // Only collect garbage in these two directories. This way, no files that do not belong to
             // the NixOS installation are deleted. Lanzatool takes full control over the esp/EFI/nixos
@@ -100,6 +103,18 @@ impl Installer {
                         .and_then(|n| n.to_str())
                         .map_or(false, |n| n.starts_with("nixos-"))
                 })?;
+        } else {
+            // Garbage collection can only be disabled if there are malformed generations. If
+            // garbage collection can ever be disabled differently, the below log message most
+            // likely does not make sense anymore.
+            log::warn!(indoc::indoc! {"
+                Garbage collection is disabled because you have malformed NixOS generations that do
+                not contain a readable bootspec document.
+
+                Remove the malformed generations with `nix-env --delete-generations` to re-enable
+                garbage collection.
+            "})
+        };
 
         log::info!("Successfully installed Lanzaboote.");
         Ok(())
@@ -171,15 +186,13 @@ impl Installer {
 
                 // Ignore failing to read a generation so that old malformed generations do not stop
                 // lzbt from working.
-                if let Err(e) = &generation_result {
-                    // Semantically, this message should be a warning. However, since users might
-                    // have hundreds of old and thus malformed generations and can do little about
-                    // it, this should remain a debug message. This way the user is not spammed
-                    // with no-op warnings while still enabling debugging.
-                    log::debug!(
-                        "Ignoring generation {} because it's malformed: {e:#}",
-                        link.version
-                    );
+                if generation_result.is_err() {
+                    // If there is ANY malformed generation present, completely disable all garbage
+                    // collection to protect the old generations from being deleted. The user has
+                    // to manually intervene by getting rid of the old generations to re-enable
+                    // garbage collection. This safeguard against catastrophic failure in case of
+                    // unhandled upstream changes to NixOS.
+                    self.enable_gc = false;
                 }
 
                 generation_result.ok()