Ensure /dev is mounted before losetup is called

Not a race condition, but more of a timing issue. Just needed to make
sure the /dev mount was happening before any of the losetup calls.

Fixes #352

Signed-off-by: Brad P. Crochet <brad@redhat.com>

rh-pre-commit.version: 2.2.0
rh-pre-commit.check-secrets: ENABLED

lib/src/blockdev.rs

@@ -13,6 +13,10 @@ 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";
+
 #[derive(Debug, Deserialize)]
 struct DevicesOutput {
     blockdevices: Vec<Device>,
@@ -80,9 +84,21 @@ 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(
+        "none",
+        DEV_MOUNT_POINT.into(),
+        crate::mount::FilesystemType::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

@@ -1069,6 +1069,11 @@ async fn prepare_install(
 
     ensure_var()?;
     setup_tmp_mounts()?;
+    crate::mount::ensure_mount(
+        "none",
+        Utf8Path::new("/dev"),
+        crate::mount::FilesystemType::DevTmpFs,
+    )?;
 
     // Even though we require running in a container, the mounts we create should be specific
     // to this process, so let's enter a private mountns to avoid leaking them.

lib/src/mount.rs

@@ -4,6 +4,7 @@ use anyhow::{anyhow, Context, Result};
 use camino::Utf8Path;
 use fn_error_context::context;
 use serde::Deserialize;
+use std::fmt;
 
 use crate::task::Task;
 
@@ -17,6 +18,19 @@ pub(crate) struct Filesystem {
     pub(crate) uuid: Option<String>,
 }
 
+#[derive(Deserialize, Debug)]
+pub(crate) enum FilesystemType {
+    DevTmpFs,
+}
+
+impl fmt::Display for FilesystemType {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            FilesystemType::DevTmpFs => write!(f, "devtmpfs"),
+        }
+    }
+}
+
 #[derive(Deserialize, Debug)]
 pub(crate) struct Findmnt {
     pub(crate) filesystems: Vec<Filesystem>,
@@ -57,3 +71,13 @@ pub(crate) fn mount(dev: &str, target: &Utf8Path) -> Result<()> {
         [dev, target.as_str()],
     )
 }
+
+/// Create the target directory if it does not exist, then mount the specified filesystem
+pub(crate) fn ensure_mount(dev: &str, target: &Utf8Path, fstype: FilesystemType) -> Result<()> {
+    std::fs::create_dir_all(target)?;
+    Task::new(format!("Mounting {fstype} {target}"), "mount")
+        .args(["-t", format!("{fstype}").as_str(), dev, target.as_str()])
+        .quiet()
+        .run()?;
+    Ok(())
+}