Move /dev mounting to loopback

lib/src/blockdev.rs

@@ -13,6 +13,11 @@ use std::os::unix::io::AsRawFd;
 use std::path::Path;
 use std::process::Command;
 
+/// The mount path and type for devtmpfs
+#[cfg(feature = "install")]
+const DEV_MOUNT_POINT: &str = "/dev";
+const DEVTMPFS: &str = "devtmpfs";
+
 #[derive(Debug, Deserialize)]
 struct DevicesOutput {
     blockdevices: Vec<Device>,
@@ -80,9 +85,17 @@ pub(crate) struct LoopbackDevice {
     pub(crate) dev: Option<Utf8PathBuf>,
 }
 
+// Ensure that `/dev` directory exists and is mounted.
+fn ensure_dev_mounted() -> Result<()> {
+    crate::mount::ensure_mount(DEVTMPFS, DEV_MOUNT_POINT, DEVTMPFS)?;
+    Ok(())
+}
+
 impl LoopbackDevice {
     // Create a new loopback block device targeting the provided file path.
     pub(crate) fn new(path: &Path) -> Result<Self> {
+        // Ensure /dev exists and is mounted
+        ensure_dev_mounted()?;
         let dev = Task::new("losetup", "losetup")
             .args(["--show", "--direct-io=on", "-P", "--find"])
             .arg(path)

lib/src/install.rs

@@ -58,9 +58,6 @@ const SELINUXFS: &str = "/sys/fs/selinux";
 #[cfg(feature = "install")]
 const EFIVARFS: &str = "/sys/firmware/efi/efivars";
 pub(crate) const ARCH_USES_EFI: bool = cfg!(any(target_arch = "x86_64", target_arch = "aarch64"));
-/// The mount path for devtmpfs
-#[cfg(feature = "install")]
-const DEVTMPFS: &str = "/dev";
 
 /// Kernel argument used to specify we want the rootfs mounted read-write by default
 const RW_KARG: &str = "rw";
@@ -1079,14 +1076,6 @@ async fn prepare_install(
         super::cli::ensure_self_unshared_mount_namespace().await?;
     }
 
-    // We need to ensure that /dev is mounted before we get to any losetup tasks
-    for (fstype, fspath) in [("devtmpfs", DEVTMPFS)] {
-        let _ = Task::new(format!("Mounting {fstype} {fspath}"), "mount")
-            .args(["-t", fstype, fstype, fspath])
-            .quiet()
-            .run();
-    }
-
     setup_sys_mount("efivarfs", EFIVARFS)?;
 
     // Now, deal with SELinux state.

lib/src/mount.rs

@@ -57,3 +57,19 @@ pub(crate) fn mount(dev: &str, target: &Utf8Path) -> Result<()> {
         [dev, target.as_str()],
     )
 }
+
+// Ensure the `/dev` directory exists.
+fn ensure_mountpoint(target: &str) -> Result<()> {
+    std::fs::create_dir_all(target)?;
+    Ok(())
+}
+
+/// General mount that also checks that mount path exists
+pub(crate) fn ensure_mount(dev: &str, target: &str, fstype: &str) -> Result<()> {
+    ensure_mountpoint(target)?;
+    Task::new(format!("Mounting {fstype} {target}"), "mount")
+        .args(["-t", fstype, dev, target])
+        .quiet()
+        .run()?;
+    Ok(())
+}