[PATCH proxmox v3 01/10] proxmox-sys: expose msync to flush mmapped contents to filesystem

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

Allows to flush all in-memory contents of the mmapped file back to
the filesystem using msync [0] given the semantics provided via the
`MS_*` flags.
Without this the contents are not guaranteed to be persisted to the
backing file until unmapped, which could lead to data loss on system
crash or OOM situations.

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

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 proxmox-sys/src/mmap.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/proxmox-sys/src/mmap.rs b/proxmox-sys/src/mmap.rs
index 8b8ad8a6..e15ca1db 100644
--- a/proxmox-sys/src/mmap.rs
+++ b/proxmox-sys/src/mmap.rs
@@ -56,6 +56,18 @@ impl<T> Mmap<T> {
             len: count,
         })
     }
+
+    /// Flush all in-memory contents to the backing file.
+    pub fn msync(&self, flags: mman::MsFlags) -> io::Result<()> {
+        unsafe {
+            mman::msync(
+                self.data.cast::<core::ffi::c_void>(),
+                self.len * mem::size_of::<T>(),
+                flags,
+            )
+        }
+        .map_err(SysError::into_io_error)
+    }
 }
 
 impl<T> std::ops::Deref for Mmap<T> {
-- 
2.47.3