crates/triggers: Add OsEnv

crates/triggers/src/lib.rs

@@ -10,6 +10,7 @@ use format::Trigger;
 use thiserror::Error;
 
 pub mod format;
+pub mod osenv;
 
 /// Grouped management of a set of triggers
 pub struct Collection<'a> {

crates/triggers/src/osenv.rs

@@ -0,0 +1,67 @@
+// SPDX-FileCopyrightText: Copyright © 2020-2024 Serpent OS Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+use std::os::linux::fs::MetadataExt;
+use std::path::Path;
+use std::{fs, io};
+
+use serde::Deserialize;
+
+/// The root directory as seen by the init process.
+const ROOT_FILE: &str = "proc/1/root";
+
+/// A canary file we create in live images.
+const LIVE_FILE: &str = "run/livedev";
+
+/// Describes a special status the operating system may be in.
+#[derive(Debug, Deserialize)]
+pub enum OsEnv {
+    /// The operating system is inside a container.
+    Container,
+
+    /// The operating system in running as a live
+    /// (and ephemeral) image.
+    Live,
+}
+
+impl OsEnv {
+    /// Detects the environment of the operating system
+    /// by analyzing the root directory content ("/").
+    pub fn detect() -> io::Result<Option<Self>> {
+        Self::detect_from_root(Path::new("/"))
+    }
+
+    /// Detects the environment of the operating system
+    /// by analyzing a sysroot directory.
+    pub fn detect_from_root(root: &Path) -> io::Result<Option<Self>> {
+        if Self::is_container(root)? {
+            return Ok(Some(Self::Container));
+        }
+        if Self::is_live(root)? {
+            return Ok(Some(Self::Live));
+        }
+        Ok(None)
+    }
+
+    fn is_container(root: &Path) -> io::Result<bool> {
+        // The logic above is heuristic and I'm not sure
+        // it works in all cases, particularly when containers
+        // are designed to be transparent.
+        // Anyway, the principle is to check that the "real" root
+        // directory and the root seen by the init process are the same.
+        let proc_root = fs::metadata(root)?;
+        let proc_meta = fs::metadata(root.join(ROOT_FILE))?;
+        if proc_root.st_dev() != proc_meta.st_dev() {
+            return Ok(true);
+        }
+        if proc_root.st_ino() != proc_meta.st_ino() {
+            return Ok(true);
+        }
+        Ok(false)
+    }
+
+    fn is_live(root: &Path) -> io::Result<bool> {
+        root.join(LIVE_FILE).try_exists()
+    }
+}