filetree: add failpoint when doing exchange

Inspired by #669 (comment)

Cargo.toml

@@ -25,6 +25,7 @@ camino = "1.1.7"
 chrono = { version = "0.4.38", features = ["serde"] }
 clap = { version = "3.2", default-features = false, features = ["cargo", "derive", "std", "suggestions"] }
 env_logger = "0.10"
+fail = { version = "0.5", features = ["failpoints"] }
 fn-error-context = "0.2.1"
 fs2 = "0.4.3"
 hex = "0.4.3"

src/failpoints.rs

@@ -0,0 +1,21 @@
+//! Wrappers and utilities on top of the `fail` crate.
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+/// TODO: Use https://github.com/tikv/fail-rs/pull/68 once it merges
+/// copy from https://github.com/coreos/rpm-ostree/commit/aa8d7fb0ceaabfaf10252180e2ddee049d07aae3#diff-adcc419e139605fae34d17b31418dbaf515af2fe9fb766fcbdb2eaad862b3daa
+#[macro_export]
+macro_rules! try_fail_point {
+    ($name:expr) => {{
+        if let Some(e) = fail::eval($name, |msg| {
+            let msg = msg.unwrap_or_else(|| "synthetic failpoint".to_string());
+            anyhow::Error::msg(msg)
+        }) {
+            return Err(From::from(e));
+        }
+    }};
+    ($name:expr, $cond:expr) => {{
+        if $cond {
+            $crate::try_fail_point!($name);
+        }
+    }};
+}

src/filetree.rs

@@ -328,6 +328,7 @@ pub(crate) fn apply_diff(
     diff: &FileTreeDiff,
     opts: Option<&ApplyUpdateOptions>,
 ) -> Result<()> {
+    println!("{diff:?}");
     let default_opts = ApplyUpdateOptions {
         ..Default::default()
     };
@@ -382,6 +383,7 @@ pub(crate) fn apply_diff(
             .with_context(|| format!("copying {:?} to {:?}", path, path_tmp))?;
     }
 
+    println!("{updates:?}");
     // do local exchange or rename
     for (dst, tmp) in updates.iter() {
         let dst = dst.as_std_path();
@@ -395,6 +397,7 @@ pub(crate) fn apply_diff(
                 .local_rename(tmp, dst)
                 .with_context(|| format!("rename for {} and {:?}", tmp, dst))?;
         }
+        crate::try_fail_point!("exchange");
     }
     // Ensure all of the updates & changes are written persistently to disk
     if !opts.skip_sync {
@@ -705,7 +708,6 @@ mod tests {
             let b_btime_foo_new = fs::metadata(pb.join(foo))?.created()?;
             assert_eq!(b_btime_foo_new, b_btime_foo);
         }
-
         Ok(())
     }
 }

src/main.rs

@@ -24,6 +24,7 @@ mod component;
 mod coreos;
 #[cfg(any(target_arch = "x86_64", target_arch = "aarch64"))]
 mod efi;
+mod failpoints;
 mod filesystem;
 mod filetree;
 #[cfg(any(

tests/e2e-update/e2e-update-in-vm.sh

@@ -67,6 +67,11 @@ tmpefimount=$(mount_tmp_efi)
 
 assert_not_has_file ${tmpefimount}/EFI/fedora/test-bootupd.efi
 
+if env FAILPOINTS='exchange=return' bootupctl update -vvv 2>err.txt; then
+    fatal "should have errored"
+fi
+assert_file_has_content_literal err.txt "error: synthetic failpoint"
+
 bootupctl update | tee out.txt
 assert_file_has_content out.txt "Previous EFI: .*"
 assert_file_has_content out.txt "Updated EFI: ${TARGET_GRUB_PKG}.*,test-bootupd-payload-1.0"