[pbs-devel] [PATCH proxmox-backup] api: chunk reader: make reading from filesystem fully async

[Christian Ebner]

Blocking the thread is problematic here and must be avoided, so
read the chunk data via tokio::fs::read() instead of std::fs::read()
and make the full loading from filesystem branch async.

Encountered while investigating a user provided backtrace looking for
possible causes of hanging backups reported in [0].

[0] https://forum.proxmox.com/threads/176444/post-819858

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
 src/api2/reader/mod.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/api2/reader/mod.rs b/src/api2/reader/mod.rs
index f7adc366f..1e74b0758 100644
--- a/src/api2/reader/mod.rs
+++ b/src/api2/reader/mod.rs
@@ -321,7 +321,7 @@ fn download_chunk(
         }
 
         let body = match &env.backend {
-            DatastoreBackend::Filesystem => load_from_filesystem(env, &digest)?,
+            DatastoreBackend::Filesystem => load_from_filesystem(env, &digest).await?,
             DatastoreBackend::S3(s3_client) => match env.datastore.cache() {
                 None => fetch_from_object_store(s3_client, &digest).await?,
                 Some(cache) => {
@@ -357,13 +357,14 @@ async fn fetch_from_object_store(s3_client: &S3Client, digest: &[u8; 32]) -> Res
     bail!("cannot find chunk with digest {}", hex::encode(digest));
 }
 
-fn load_from_filesystem(env: &ReaderEnvironment, digest: &[u8; 32]) -> Result<Body, Error> {
+async fn load_from_filesystem(env: &ReaderEnvironment, digest: &[u8; 32]) -> Result<Body, Error> {
     let (path, _) = env.datastore.chunk_path(digest);
     let path2 = path.clone();
 
     env.debug(format!("download chunk {path:?}"));
 
-    let data = proxmox_async::runtime::block_in_place(|| std::fs::read(path))
+    let data = tokio::fs::read(path)
+        .await
         .map_err(move |err| http_err!(BAD_REQUEST, "reading file {path2:?} failed: {err}"))?;
     Ok(Body::from(data))
 }
-- 
2.47.3