From fb273dd54f77dfd9ae5da1e7078b860014a8fb85 Mon Sep 17 00:00:00 2001
From: "re:fi.64" <hello@refi64.dev>
Date: Sat, 26 Sep 2026 18:06:21 -0500
Subject: [PATCH] Fix race when querying a devnode major/minor before it exists

Devnode points to the symlink, which is created asynchronously by udev,
so when this code runs it might not actually exist yet.
---
 src/service.rs | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/src/service.rs b/src/service.rs
index e6eac1d..203710b 100644
--- a/src/service.rs
+++ b/src/service.rs
@@ -44,13 +44,33 @@ impl<T: zvariant::Type> IntoTonicResult<T> for OperationResult<T> {
     }
 }
 
+fn major_minor_from_stat(stat: rustix::fs::Stat) -> (u32, u32) {
+    (
+        rustix::fs::major(stat.st_rdev),
+        rustix::fs::minor(stat.st_rdev),
+    )
+}
+
 fn devnode_major_minor(path: &str) -> tonic::Result<(u32, u32)> {
     let stat = rustix::fs::stat(path)
         .map_err(|e| tonic::Status::internal(format!("stat {path}: {e:?}")))?;
-    Ok((
-        rustix::fs::major(stat.st_rdev),
-        rustix::fs::minor(stat.st_rdev),
-    ))
+    Ok(major_minor_from_stat(stat))
+}
+
+async fn devnode_major_minor_retry_missing(path: &str) -> tonic::Result<(u32, u32)> {
+    for _ in 0..50 {
+        match rustix::fs::stat(path) {
+            Ok(stat) => return Ok(major_minor_from_stat(stat)),
+            Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
+                tokio::time::sleep(Duration::from_millis(100)).await;
+            }
+            Err(e) => return Err(tonic::Status::internal(format!("stat {path}: {e:?}"))),
+        }
+    }
+
+    Err(tonic::Status::deadline_exceeded(format!(
+        "waiting for devnode {path}"
+    )))
 }
 
 fn get_size_bytes_unsigned(size_bytes: i64) -> tonic::Result<u64> {
@@ -415,7 +435,7 @@ impl lvmd::lv_service_server::LvService for Service {
 
         info!("retrieving devnode information");
         let devnode = fs.proxy.devnode().await.into_tonic_result()?;
-        let (dev_major, dev_minor) = devnode_major_minor(&devnode)?;
+        let (dev_major, dev_minor) = devnode_major_minor_retry_missing(&devnode).await?;
 
         #[allow(deprecated)]
         Ok(tonic::Response::new(lvmd::CreateLvResponse {
@@ -595,7 +615,7 @@ impl lvmd::lv_service_server::LvService for Service {
 
         info!("retrieving devnode information");
         let devnode = snapshot.proxy.devnode().await.into_tonic_result()?;
-        let (dev_major, dev_minor) = devnode_major_minor(&devnode)?;
+        let (dev_major, dev_minor) = devnode_major_minor_retry_missing(&devnode).await?;
 
         #[allow(deprecated)]
         Ok(tonic::Response::new(lvmd::CreateLvSnapshotResponse {
-- 
2.51.2