[PATCH proxmox] shared-memory: flush contents of newly created mmap file

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

The man page for mmap [0] states, that mappings create with
`MAP_SHARED` are not carried to the underlying file directly.

To avoid possible races between creating and initializing a new
mmapped file and opening while checking the header of this file,
msync the contents after init but before persisting the shared
memory backed file.

[0] https://man7.org/linux/man-pages/man2/mmap.2.html

Fixes: https://forum.proxmox.com/threads/182948/
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 proxmox-shared-memory/src/lib.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/proxmox-shared-memory/src/lib.rs b/proxmox-shared-memory/src/lib.rs
index 495812ef..4838ab42 100644
--- a/proxmox-shared-memory/src/lib.rs
+++ b/proxmox-shared-memory/src/lib.rs
@@ -190,6 +190,10 @@ impl<T: Sized + Init> SharedMemory<T> {
 
         let mmap = mmap_file(&mut file, true)?;
 
+        if skip_tmpfs_check {
+            mmap.msync(MsFlags::MS_SYNC)?;
+        }
+
         let res = {
             let path = CString::new(path.as_os_str().as_bytes())?;
             Errno::result(unsafe {
-- 
2.47.3