waiting for device to exist

It might be possible that the storage device does not probe fast enough
causing an error when trying to mount it. Thus, we should wait for it
passively before proceeding with the code.

Signed-off-by: Fabian Pfitzner <f.pfitzner@pengutronix.de>

Author: Fabian Pfitzner

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;
 
@@ -120,9 +120,7 @@ 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);
-    }
+    wait_for_device(root_device)?;
 
     let mut data_blocks = "";
     let mut data_sectors = "";

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 mut counter = 0;
+    while !Path::new(&root_device).exists() {
+        let duration = time::Duration::from_millis(5);
+
+        if counter > 1000 {
+            return Err("timout reached while waiting for the device".into());
+        }
+
+        thread::sleep(duration);
+        counter += 1;
+    }
+    Ok(())
+}
+
 /*
  * 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>,
@@ -49,6 +49,13 @@ pub fn mount_root(options: &CmdlineOptions) -> Result<()> {
         return Err("root= not found in /proc/cmdline".into());
     }
 
+    if options.rootfstype != Some("nfs".to_string()) &&
+        options.rootfstype != Some("9p".to_string())
+    {
+        let root_device = options.root.as_ref().ok_or("No root device argument")?;
+        wait_for_device(root_device)?;
+    }
+
     mkdir("/root")?;
 
     debug!(