misc: test_infra: streamline #[source] and Error impl

This streamlines the Error implementation in the Cloud Hypervisor code
base to match the remaining parts so that everything follows the agreed
conventions. These are leftovers missed in the previous commits.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

Cargo.lock

@@ -2068,6 +2068,7 @@ dependencies = [
  "serde",
  "serde_json",
  "ssh2",
+ "thiserror 2.0.6",
  "vmm-sys-util",
  "wait-timeout",
 ]

test_infra/Cargo.toml

@@ -12,5 +12,6 @@ once_cell = "1.20.2"
 serde = { version = "1.0.208", features = ["derive", "rc"] }
 serde_json = { workspace = true }
 ssh2 = { version = "0.9.4", features = ["vendored-openssl"] }
+thiserror = "2.0.6"
 vmm-sys-util = { workspace = true }
 wait-timeout = "0.2.0"

test_infra/src/lib.rs

@@ -21,27 +21,40 @@ use std::{env, fmt, fs, io, thread};
 use once_cell::sync::Lazy;
 use serde_json::Value;
 use ssh2::Session;
+use thiserror::Error;
 use vmm_sys_util::tempdir::TempDir;
 use wait_timeout::ChildExt;
 
-#[derive(Debug)]
+#[derive(Error, Debug)]
 pub enum WaitTimeoutError {
+    #[error("timeout")]
     Timedout,
+    #[error("exit status indicates failure")]
     ExitStatus,
-    General(std::io::Error),
+    #[error("general failure: {0}")]
+    General(#[source] std::io::Error),
 }
 
-#[derive(Debug)]
+#[derive(Error, Debug)]
 pub enum Error {
-    Parsing(std::num::ParseIntError),
-    SshCommand(SshCommandError),
-    WaitForBoot(WaitForBootError),
-    EthrLogFile(std::io::Error),
+    #[error("Failed to parse: {0}")]
+    Parsing(#[source] std::num::ParseIntError),
+    #[error("ssh command failed: {0}")]
+    SshCommand(#[source] SshCommandError),
+    #[error("waiting for boot failed: {0}")]
+    WaitForBoot(#[source] WaitForBootError),
+    #[error("reading log file failed: {0}")]
+    EthrLogFile(#[source] std::io::Error),
+    #[error("parsing log file failed")]
     EthrLogParse,
+    #[error("parsing fio output failed")]
     FioOutputParse,
+    #[error("parsing iperf3 output failed")]
     Iperf3Parse,
-    Spawn(std::io::Error),
-    WaitTimeout(WaitTimeoutError),
+    #[error("spawning process failed: {0}")]
+    Spawn(#[source] std::io::Error),
+    #[error("waiting for timeout failed: {0}")]
+    WaitTimeout(#[source] WaitTimeoutError),
 }
 
 impl From<SshCommandError> for Error {
@@ -67,13 +80,18 @@ pub const DEFAULT_TCP_LISTENER_MESSAGE: &str = "booted";
 pub const DEFAULT_TCP_LISTENER_PORT: u16 = 8000;
 pub const DEFAULT_TCP_LISTENER_TIMEOUT: i32 = 120;
 
-#[derive(Debug)]
+#[derive(Error, Debug)]
 pub enum WaitForBootError {
-    EpollWait(std::io::Error),
-    Listen(std::io::Error),
+    #[error("Failed to wait for epoll: {0}")]
+    EpollWait(#[source] std::io::Error),
+    #[error("Failed to listen for boot: {0}")]
+    Listen(#[source] std::io::Error),
+    #[error("Epoll wait timeout")]
     EpollWaitTimeout,
+    #[error("wrong guest address")]
     WrongGuestAddr,
-    Accept(std::io::Error),
+    #[error("Failed to accept a TCP request: {0}")]
+    Accept(#[source] std::io::Error),
 }
 
 impl GuestNetworkConfig {
@@ -532,21 +550,34 @@ pub struct PasswordAuth {
 pub const DEFAULT_SSH_RETRIES: u8 = 6;
 pub const DEFAULT_SSH_TIMEOUT: u8 = 10;
 
-#[derive(Debug)]
+#[derive(Error, Debug)]
 pub enum SshCommandError {
-    Connection(std::io::Error),
-    Handshake(ssh2::Error),
-    Authentication(ssh2::Error),
-    ChannelSession(ssh2::Error),
-    Command(ssh2::Error),
-    ExitStatus(ssh2::Error),
+    #[error("ssh connection failed: {0}")]
+    Connection(#[source] std::io::Error),
+    #[error("ssh handshake failed: {0}")]
+    Handshake(#[source] ssh2::Error),
+    #[error("ssh authentication failed: {0}")]
+    Authentication(#[source] ssh2::Error),
+    #[error("ssh channel session failed: {0}")]
+    ChannelSession(#[source] ssh2::Error),
+    #[error("ssh command failed: {0}")]
+    Command(#[source] ssh2::Error),
+    #[error("retrieving exit status from ssh command failed: {0}")]
+    ExitStatus(#[source] ssh2::Error),
+    #[error("the exit code indicates failure: {0}")]
     NonZeroExitStatus(i32),
-    FileRead(std::io::Error),
-    FileMetadata(std::io::Error),
-    ScpSend(ssh2::Error),
-    WriteAll(std::io::Error),
-    SendEof(ssh2::Error),
-    WaitEof(ssh2::Error),
+    #[error("failed to read file: {0}")]
+    FileRead(#[source] std::io::Error),
+    #[error("failed to read metadata: {0}")]
+    FileMetadata(#[source] std::io::Error),
+    #[error("scp send failed: {0}")]
+    ScpSend(#[source] ssh2::Error),
+    #[error("scp write failed: {0}")]
+    WriteAll(#[source] std::io::Error),
+    #[error("scp send EOF failed: {0}")]
+    SendEof(#[source] ssh2::Error),
+    #[error("scp wait EOF failed: {0}")]
+    WaitEof(#[source] ssh2::Error),
 }
 
 fn scp_to_guest_with_auth(