ephemeral: Two debug improvement patches

crates/kit/src/qemu.rs

@@ -907,6 +907,8 @@ pub struct VirtiofsConfig {
     pub debug: bool,
     /// Mount as read-only
     pub readonly: bool,
+    /// Optional log file path for virtiofsd output
+    pub log_file: Option<Utf8PathBuf>,
 }
 
 impl Default for VirtiofsConfig {
@@ -917,6 +919,7 @@ impl Default for VirtiofsConfig {
             debug: false,
             // We don't need to write to this, there's a transient overlay
             readonly: true,
+            log_file: None,
         }
     }
 }
@@ -998,8 +1001,31 @@ pub async fn spawn_virtiofsd_async(config: &VirtiofsConfig) -> Result<tokio::pro
     // but we want to be compatible with older virtiofsd too.
     cmd.arg("--inode-file-handles=fallback");
 
-    cmd.stdout(std::process::Stdio::piped());
-    cmd.stderr(std::process::Stdio::piped());
+    // Configure output redirection
+    if let Some(log_file) = &config.log_file {
+        // Create/open log file for both stdout and stderr
+        let tokio_file = tokio::fs::OpenOptions::new()
+            .create(true)
+            .append(true)
+            .open(log_file)
+            .await
+            .with_context(|| format!("Failed to open virtiofsd log file: {}", log_file))?;
+
+        let log_file_handle = tokio_file.into_std().await;
+
+        // Clone for stderr
+        let stderr_handle = log_file_handle
+            .try_clone()
+            .with_context(|| "Failed to clone log file handle for stderr")?;
+
+        cmd.stdout(std::process::Stdio::from(log_file_handle));
+        cmd.stderr(std::process::Stdio::from(stderr_handle));
+
+        debug!("virtiofsd output will be logged to: {}", log_file);
+    } else {
+        cmd.stdout(std::process::Stdio::piped());
+        cmd.stderr(std::process::Stdio::piped());
+    }
 
     let child = cmd.spawn().with_context(|| {
         format!(
@@ -1009,8 +1035,8 @@ pub async fn spawn_virtiofsd_async(config: &VirtiofsConfig) -> Result<tokio::pro
     })?;
 
     debug!(
-        "Spawned virtiofsd: binary={}, socket={}, shared_dir={}, debug={}",
-        virtiofsd_binary, config.socket_path, config.shared_dir, config.debug
+        "Spawned virtiofsd: binary={}, socket={}, shared_dir={}, debug={}, log_file={:?}",
+        virtiofsd_binary, config.socket_path, config.shared_dir, config.debug, config.log_file
     );
 
     Ok(child)

crates/kit/src/run_ephemeral.rs

@@ -823,6 +823,7 @@ pub(crate) async fn run_impl(opts: RunEphemeralOpts) -> Result<()> {
                 shared_dir: source_path,
                 debug: false,
                 readonly: is_readonly,
+                log_file: Some(format!("/run/virtiofsd-{}.log", mount_name_str).into()),
             };
             additional_mounts.push((virtiofsd_config, tag.clone()));
 
@@ -892,6 +893,35 @@ WantedBy=local-fs.target
     let default_wantsdir = format!("{target_unitdir}/default.target.wants");
     fs::create_dir_all(&default_wantsdir)?;
 
+    // Create systemd unit to stream journal to virtio-serial device
+    let journal_stream_unit = r#"[Unit]
+Description=Stream systemd journal to host via virtio-serial
+DefaultDependencies=no
+After=systemd-journald.service dev-virtio\x2dports-org.bcvk.journal.device
+Requires=systemd-journald.service dev-virtio\x2dports-org.bcvk.journal.device
+
+[Service]
+Type=simple
+ExecStart=/usr/bin/journalctl -f -o short-precise --no-pager
+StandardOutput=file:/dev/virtio-ports/org.bcvk.journal
+StandardError=file:/dev/virtio-ports/org.bcvk.journal
+Restart=always
+RestartSec=1s
+
+[Install]
+WantedBy=sysinit.target
+"#;
+    let journal_unit_path = format!("{target_unitdir}/bcvk-journal-stream.service");
+    tokio::fs::write(&journal_unit_path, journal_stream_unit).await?;
+    debug!("Created journal streaming unit at {journal_unit_path}");
+
+    // Enable the journal streaming unit
+    let sysinit_wantsdir = format!("{target_unitdir}/sysinit.target.wants");
+    tokio::fs::create_dir_all(&sysinit_wantsdir).await?;
+    let journal_wants_link = format!("{sysinit_wantsdir}/bcvk-journal-stream.service");
+    tokio::fs::symlink("../bcvk-journal-stream.service", &journal_wants_link).await?;
+    debug!("Enabled journal streaming unit in sysinit.target.wants");
+
     match opts.common.execute.as_slice() {
         [] => {}
         elts => {
@@ -945,6 +975,8 @@ StandardOutput=file:/dev/virtio-ports/executestatus
     // Prepare main virtiofsd config for the source image (will be spawned by QEMU)
     let mut main_virtiofsd_config = qemu::VirtiofsConfig::default();
     main_virtiofsd_config.debug = std::env::var("DEBUG_MODE").is_ok();
+    // Always log virtiofsd output for debugging
+    main_virtiofsd_config.log_file = Some("/run/virtiofsd.log".into());
 
     std::fs::create_dir_all(CONTAINER_STATEDIR)?;
 
@@ -1092,6 +1124,10 @@ Options=
         .set_kernel_cmdline(kernel_cmdline)
         .set_console(opts.common.console);
 
+    // Add virtio-serial device for journal streaming
+    qemu_config.add_virtio_serial_out("org.bcvk.journal", "/run/journal.log".to_string(), false);
+    debug!("Added virtio-serial device for journal streaming to /run/journal.log");
+
     if opts.common.ssh_keygen {
         qemu_config.enable_ssh_access(None); // Use default port 2222
         debug!("Enabled SSH port forwarding: host port 2222 -> guest port 22");

docs/src/man/bcvk-ephemeral-run.md

@@ -173,6 +173,48 @@ Development workflow example:
 
     # VM automatically cleans up when stopped due to --rm flag
 
+# DEBUGGING
+
+When troubleshooting ephemeral VM issues, bcvk provides several debugging logs that can be accessed from within the container.
+
+## Guest Journal Log
+
+The systemd journal from the guest VM is automatically streamed to `/run/journal.log` inside the container. This log captures all boot messages, service startup events, and system errors from the VM's perspective.
+
+To view the journal log:
+
+    # For a running detached VM
+    podman exec <container-id> tail -f /run/journal.log
+
+    # View specific systemd service messages
+    podman exec <container-id> grep "dbus-broker" /run/journal.log
+
+    # Save journal for offline analysis
+    podman exec <container-id> cat /run/journal.log > guest-journal.log
+
+The journal log is particularly useful for:
+- Diagnosing boot failures and systemd service issues
+- Investigating permission denied errors
+- Understanding VM initialization problems
+- Debugging network and device configuration
+
+## Virtiofsd Logs
+
+The virtiofsd daemon logs are written to `/run/virtiofsd.log` and `/run/virtiofsd-<mount-name>.log` for each filesystem mount. These logs show filesystem sharing operations between the container and VM.
+
+To view virtiofsd logs:
+
+    # Main virtiofsd log
+    podman exec <container-id> cat /run/virtiofsd.log
+
+    # Logs for additional bind mounts
+    podman exec <container-id> cat /run/virtiofsd-workspace.log
+
+Virtiofsd logs are helpful for:
+- Debugging filesystem access issues
+- Understanding file handle support warnings
+- Investigating mount-related errors
+
 # SEE ALSO
 
 **bcvk**(8)