From 0af314b295f70fdf107524b08063f4d36fb4eeb6 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Mon, 14 Mar 2022 11:54:00 +0100
Subject: [PATCH] Add comment for fsync

---
 src/model/block.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/model/block.rs b/src/model/block.rs
index 8329bb6f..a41daa64 100644
--- a/src/model/block.rs
+++ b/src/model/block.rs
@@ -902,6 +902,11 @@ impl BlockManagerLocked {
 			fs::remove_file(to_delete).await?;
 		}
 
+		// We want to ensure that when this function returns, data is properly persisted
+		// to disk. The first step is the sync_all above that does an fsync on the data file.
+		// Now, we do an fsync on the containing directory, to ensure that the rename
+		// is persisted properly. See:
+		// http://thedjbway.b0llix.net/qmail/syncdir.html
 		let dir = fs::OpenOptions::new()
 			.read(true)
 			.mode(0)