Replace env var daemon spawning with hidden run-daemon subcommand

Signed-off-by: Cong Wang <cwang@multikernel.io>

Author: congwang-mk

src/daemon.rs

@@ -388,10 +388,15 @@ pub fn start_daemon_background(base_path: &Path, storage_path: &Path) -> std::io
     // proper fd inheritance control — stdin/stdout/stderr are /dev/null
     // so callers that capture output won't block.
     let exe = std::env::current_exe()?;
-    let env_val = format!("{}:{}", base_path.display(), storage_path.display());
 
     Command::new(exe)
-        .env("_BRANCHFS_DAEMON", env_val)
+        .args([
+            "run-daemon",
+            "--base",
+            &base_path.to_string_lossy(),
+            "--storage",
+            &storage_path.to_string_lossy(),
+        ])
         .stdin(Stdio::null())
         .stdout(Stdio::null())
         .stderr(Stdio::null())

src/main.rs

@@ -88,6 +88,16 @@ enum Commands {
         #[arg(long, default_value = "/var/lib/branchfs")]
         storage: PathBuf,
     },
+
+    /// Internal: run the daemon (used by `mount` to spawn the daemon process)
+    #[command(hide = true)]
+    RunDaemon {
+        #[arg(long)]
+        base: PathBuf,
+
+        #[arg(long)]
+        storage: PathBuf,
+    },
 }
 
 fn get_socket_path(storage: &Path) -> PathBuf {
@@ -118,23 +128,6 @@ fn get_mount_branch(storage: &Path, mountpoint: &Path) -> Result<String> {
 
 fn main() -> Result<()> {
     env_logger::init();
-
-    // Re-exec entry point: when spawned as a daemon by start_daemon_background(),
-    // we skip CLI parsing and run the daemon loop directly.
-    if let Ok(val) = std::env::var("_BRANCHFS_DAEMON") {
-        let parts: Vec<&str> = val.splitn(2, ':').collect();
-        if parts.len() == 2 {
-            let base = PathBuf::from(parts[0]);
-            let storage = PathBuf::from(parts[1]);
-            let daemon = daemon::Daemon::new(base.clone(), storage, base)
-                .map_err(|e| anyhow::anyhow!("Failed to create daemon: {}", e))?;
-            daemon
-                .run()
-                .map_err(|e| anyhow::anyhow!("Daemon error: {}", e))?;
-        }
-        return Ok(());
-    }
-
     let cli = Cli::parse();
 
     match cli.command {
@@ -328,6 +321,16 @@ fn main() -> Result<()> {
                 process::exit(1);
             }
         }
+        Commands::RunDaemon { base, storage } => {
+            std::fs::create_dir_all(&storage)?;
+            let storage = storage.canonicalize()?;
+            let base = base.canonicalize()?;
+
+            let d = daemon::Daemon::new(base.clone(), storage, base)
+                .map_err(|e| anyhow::anyhow!("Failed to create daemon: {}", e))?;
+            d.run()
+                .map_err(|e| anyhow::anyhow!("Daemon error: {}", e))?;
+        }
     }
 
     Ok(())