Implemented node system statistics

MoonlightServers.Daemon/Helpers/NativeMethods.cs

@@ -0,0 +1,36 @@
+using System.Runtime.InteropServices;
+
+namespace MoonlightServers.Daemon.Helpers;
+
+internal static partial class NativeMethods
+{
+    [StructLayout(LayoutKind.Sequential)]
+    internal struct StatVfsResult
+    {
+        public ulong bsize;
+        public ulong frsize;
+        public ulong blocks;
+        public ulong bfree;
+        public ulong bavail;
+        public ulong files;
+        public ulong ffree;
+        public ulong favail;
+        public ulong fsid;
+        public ulong flag;
+        public ulong namemax;
+        private ulong __spare0;  // } kernel reserved padding —
+        private ulong __spare1;  // } never read, exist only to
+        private ulong __spare2;  // } match the 112-byte struct
+        private ulong __spare3;  // } statvfs layout on x86-64
+        private ulong __spare4;  // } Linux so the fields above
+        private ulong __spare5;  // } land at the right offsets
+    }
+
+    // SetLastError = true tells the marshaller to capture errno immediately
+    // after the call, before any other code can clobber it. Retrieve it with
+    // Marshal.GetLastPInvokeError() which maps to the thread-local errno value.
+    [LibraryImport("libc", EntryPoint = "statvfs",
+        StringMarshalling = StringMarshalling.Utf8,
+        SetLastError = true)]
+    internal static partial int StatVfs(string path, out StatVfsResult buf);
+}