[PATCH proxmox v6 07/12] s3-client: sync flush request counters on client instance drop

[Christian Ebner <c.ebner@proxmox.com>]

Persist the counter state to the shared memory backing file on s3
client destruction via a blocking msync call. This assures that any
counter updates not yet persisted since the last asynchronous msync
call are written back to the file.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 proxmox-s3-client/src/client.rs                  | 15 +++++++++++++++
 proxmox-s3-client/src/shared_request_counters.rs |  5 +++++
 2 files changed, 20 insertions(+)

diff --git a/proxmox-s3-client/src/client.rs b/proxmox-s3-client/src/client.rs
index 0ff79a63..fc883186 100644
--- a/proxmox-s3-client/src/client.rs
+++ b/proxmox-s3-client/src/client.rs
@@ -175,6 +175,21 @@ pub struct S3Client {
     request_counters: Option<Arc<SharedRequestCounters>>,
 }
 
+impl Drop for S3Client {
+    fn drop(&mut self) {
+        if let Some(counters) = &self.request_counters {
+            SHARED_COUNTER_FLUSHER
+                .write()
+                .unwrap()
+                .remove_counter(&counters.path_buf());
+
+            if let Err(err) = counters.flush() {
+                tracing::error!("flushing s3 request counters failed: {err:?}");
+            }
+        }
+    }
+}
+
 impl S3Client {
     /// Creates a new S3 client instance, connecting to the provided endpoint using https given the
     /// provided options.
diff --git a/proxmox-s3-client/src/shared_request_counters.rs b/proxmox-s3-client/src/shared_request_counters.rs
index 5c607f7c..2b5a0843 100644
--- a/proxmox-s3-client/src/shared_request_counters.rs
+++ b/proxmox-s3-client/src/shared_request_counters.rs
@@ -263,6 +263,11 @@ impl SharedRequestCounters {
         self.shared_memory.msync(MsFlags::MS_ASYNC)
     }
 
+    /// Persist in-memory contents to backing file, blocking until synced
+    pub fn flush(&self) -> Result<(), Error> {
+        self.shared_memory.msync(MsFlags::MS_SYNC)
+    }
+
     /// Path of shared memory backing file
     pub fn path_buf(&self) -> PathBuf {
         self.path.clone()
-- 
2.47.3