From d608ffeeda1a479c9dc0e5f6ad269ba07a510d7f Mon Sep 17 00:00:00 2001
From: Andrew Guschin <guschin@altlinux.org>
Date: Fri, 30 Oct 2026 03:10:41 +0400
Subject: Implement Linux proxy controller, subscription state, and CLI/TUI

---
 src/locking.rs | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 src/locking.rs

(limited to 'src/locking.rs')

diff --git a/src/locking.rs b/src/locking.rs
new file mode 100644
index 0000000..1c39471
--- /dev/null
+++ b/src/locking.rs
@@ -0,0 +1,35 @@
+use anyhow::{Context, Result, ensure};
+use std::{
+    fs::{File, OpenOptions},
+    os::fd::AsRawFd,
+    os::unix::fs::{MetadataExt, OpenOptionsExt},
+    path::Path,
+};
+
+pub fn controller_lock() -> Result<File> {
+    let directory = Path::new("/run/roentgen");
+    std::fs::create_dir_all(directory)?;
+    let metadata = std::fs::symlink_metadata(directory)?;
+    ensure!(
+        metadata.is_dir()
+            && metadata.uid() == unsafe { libc::geteuid() }
+            && metadata.mode() & 0o022 == 0,
+        "Runtime directory must be service-owned and not writable by other users"
+    );
+    let file = OpenOptions::new()
+        .create(true)
+        .truncate(false)
+        .read(true)
+        .write(true)
+        .mode(0o600)
+        .custom_flags(libc::O_NOFOLLOW)
+        .open(directory.join("controller.lock"))
+        .context("Open controller lock")?;
+    // SAFETY: file owns this live fd; flock does not retain a pointer.
+    let result = unsafe { libc::flock(file.as_raw_fd(), libc::LOCK_EX | libc::LOCK_NB) };
+    ensure!(
+        result == 0,
+        "Another controller is running; stop it before explicit recovery"
+    );
+    Ok(file)
+}
-- 
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