waiting for device to exist

src/dmverity.rs

@@ -12,7 +12,7 @@ use nix::libc::dev_t;
 use nix::sys::stat::minor;
 
 use crate::cmdline::CmdlineOptions;
-use crate::{read_file, Result};
+use crate::{read_file, wait_for_device, Result};
 
 const DM_VERSION_MAJOR: u32 = 4;
 
@@ -120,8 +120,9 @@ pub fn prepare_dmverity(options: &mut CmdlineOptions) -> Result<bool> {
         return Ok(false);
     }
     let root_device = options.root.as_ref().ok_or("No root device")?;
-    if !Path::new(&root_device).exists() {
-        return Ok(false);
+    match options.rootfstype.as_deref() {
+        Some("nfs") | Some("9p") => return Ok(false),
+        _ => wait_for_device(root_device)?,
     }
 
     let mut data_blocks = "";

src/main.rs

@@ -12,6 +12,8 @@ use std::os::fd::{AsFd, AsRawFd, RawFd};
 use std::os::unix::ffi::OsStrExt;
 use std::panic::set_hook;
 use std::path::Path;
+use std::thread;
+use std::time;
 
 use cmdline::{parse_cmdline, CmdlineOptions};
 #[cfg(feature = "dmverity")]
@@ -51,6 +53,21 @@ fn read_file(filename: &str) -> std::result::Result<String, String> {
     read_to_string(filename).map_err(|e| format!("Failed to read {filename}: {e}"))
 }
 
+fn wait_for_device(root_device: &str) -> Result<()> {
+    let duration = time::Duration::from_millis(5);
+    let path = Path::new(&root_device);
+
+    for _ in 0..1000 {
+        if path.exists() {
+            return Ok(());
+        }
+
+        thread::sleep(duration);
+    }
+
+    Err("timout reached while waiting for the device".into())
+}
+
 /*
  * Setup stdout/stderr. The kernel will create /dev/console in the
  * initramfs, so we can use that.

src/mount.rs

@@ -7,7 +7,7 @@ use log::debug;
 use nix::mount::{mount, MsFlags};
 
 use crate::cmdline::CmdlineOptions;
-use crate::{mkdir, Result};
+use crate::{mkdir, wait_for_device, Result};
 
 pub fn do_mount(
     src: Option<&str>,
@@ -45,10 +45,15 @@ pub fn mount_apivfs(dst: &str, fstype: &str) -> Result<()> {
 }
 
 pub fn mount_root(options: &CmdlineOptions) -> Result<()> {
-    if options.root.is_none() {
-        return Err("root= not found in /proc/cmdline".into());
+    let root = options
+        .root
+        .as_ref()
+        .ok_or("root= not found in /proc/cmdline")?;
+
+    match options.rootfstype.as_deref() {
+        Some("nfs") | Some("9p") => (),
+        _ => wait_for_device(root)?,
     }
-
     mkdir("/root")?;
 
     debug!(