From 81088f238e4996bb1811bd7b7dc48d9dc9f54c24 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <christian@neon.tech>
Date: Thu, 30 Mar 2023 11:16:09 +0200
Subject: [PATCH] fix: do a single write to stderr from the statvfs_ldpreload

---
 libs/statvfs_ldpreload/src/lib.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libs/statvfs_ldpreload/src/lib.rs b/libs/statvfs_ldpreload/src/lib.rs
index a884611735..aff62cfee9 100644
--- a/libs/statvfs_ldpreload/src/lib.rs
+++ b/libs/statvfs_ldpreload/src/lib.rs
@@ -74,10 +74,14 @@ pub extern "C" fn fstatvfs(_fd: libc::c_int, buf: *mut libc::statvfs64) -> libc:
         config: &config,
         invocation_number,
     };
-    eprintln!(
+    let status_line = format!(
         "statvfs_ldpreload status: {}",
         serde_json::to_string(&status).unwrap()
     );
+    // Do a single write() system call to the stderr file descriptor.
+    // The kernel should serialize it with other writes to stderr,
+    // as long as the write doesn't cross page boundary.
+    eprintln!("{}", status_line);
 
     // mock the statvfs call
     match config.mock {