mount: Add TempMount mount struct

Add a TempMount struct which mounts a device/partition on a tempdir and
automatically unmount on drop

Signed-off-by: Pragyan Poudyal <[email protected]>

Author: Johan-Liebert1

Cargo.lock

@@ -20,6 +20,8 @@ libc = { workspace = true }
 rustix = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
 tracing = { workspace = true }
+tempfile = { workspace = true }
+cap-std-ext = { workspace = true }
 
 [dev-dependencies]
 indoc = { workspace = true }

crates/mount/Cargo.toml

@@ -22,6 +22,8 @@ use rustix::{
 };
 use serde::Deserialize;
 
+pub mod tempmount;
+
 /// Well known identifier for pid 1
 pub const PID1: Pid = const {
     match Pid::from_raw(1) {

crates/mount/src/mount.rs

@@ -0,0 +1,40 @@
+use anyhow::{Context, Result};
+
+use camino::Utf8Path;
+use cap_std_ext::cap_std::{ambient_authority, fs::Dir};
+use fn_error_context::context;
+use rustix::mount::{unmount, UnmountFlags};
+
+pub struct TempMount {
+    pub dir: tempfile::TempDir,
+    pub fd: Dir,
+}
+
+impl TempMount {
+    /// Mount device/partition on a tempdir which will be automatically unmounted on drop
+    #[context("Mounting {dev}")]
+    pub fn mount_dev(dev: &str) -> Result<Self> {
+        let tempdir = tempfile::TempDir::new()?;
+
+        let utf8path = Utf8Path::from_path(tempdir.path())
+            .ok_or(anyhow::anyhow!("Failed to convert path to UTF-8 Path"))?;
+
+        crate::mount(dev, utf8path)?;
+
+        // There's a case here where if the following open fails, we won't unmount which should be
+        // unlikely
+        let fd = Dir::open_ambient_dir(tempdir.path(), ambient_authority())
+            .with_context(|| format!("Opening {:?}", tempdir.path()))?;
+
+        Ok(TempMount { dir: tempdir, fd })
+    }
+}
+
+impl Drop for TempMount {
+    fn drop(&mut self) {
+        match unmount(self.dir.path(), UnmountFlags::DETACH) {
+            Ok(_) => {}
+            Err(e) => tracing::warn!("Failed to unmount tempdir: {e:?}"),
+        }
+    }
+}