Get the host name from uname method to avoid read the file

src/Avalonia.X11/UtsName.cs

@@ -0,0 +1,105 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Avalonia.X11;
+
+internal struct UtsName : IDisposable
+{
+    // https://github.com/torvalds/linux/blob/master/include/uapi/linux/utsname.h
+    /*
+       #define __NEW_UTS_LEN 64
+
+       struct new_utsname
+       {
+        char sysname[__NEW_UTS_LEN + 1];
+        char nodename[__NEW_UTS_LEN + 1];
+        char release[__NEW_UTS_LEN + 1];
+        char version[__NEW_UTS_LEN + 1];
+        char machine[__NEW_UTS_LEN + 1];
+        char domainname[__NEW_UTS_LEN + 1];
+       };
+     */
+
+    private UtsName(IntPtr buffer)
+    {
+        _buffer = buffer;
+    }
+
+    public static UtsName GetUtsName()
+    {
+        var ntsNameStructSize = (UtsLength + 1) * FieldCount;
+
+        IntPtr buffer = Marshal.AllocHGlobal(ntsNameStructSize);
+        try
+        {
+            if (uname(buffer) != 0)
+            {
+                throw new InvalidOperationException("uname failed");
+            }
+
+            return new UtsName(buffer);
+        }
+        catch
+        {
+            Marshal.FreeHGlobal(buffer);
+            throw;
+        }
+    }
+
+    private const int SystemNameFieldIndex = 0;
+    public Span<byte> SystemNameSpan => GetValue(SystemNameFieldIndex);
+    public string SystemName => Encoding.UTF8.GetString(SystemNameSpan);
+
+    private const int NodeNameFieldIndex = 1;
+    public Span<byte> NodeNameSpan => GetValue(NodeNameFieldIndex);
+    public string NodeName => Encoding.UTF8.GetString(NodeNameSpan);
+
+    private const int ReleaseFieldIndex = 2;
+    public Span<byte> ReleaseSpan => GetValue(ReleaseFieldIndex);
+    public string Release => Encoding.UTF8.GetString(ReleaseSpan);
+
+    private const int VersionFieldIndex = 3;
+    public Span<byte> VersionSpan => GetValue(VersionFieldIndex);
+    public string Version => Encoding.UTF8.GetString(VersionSpan);
+
+    private const int MachineFieldIndex = 4;
+    public Span<byte> MachineSpan => GetValue(MachineFieldIndex);
+    public string Machine => Encoding.UTF8.GetString(MachineSpan);
+
+    private const int DomainNameFieldIndex = 5;
+    public Span<byte> DomainNameSpan => GetValue(DomainNameFieldIndex);
+    public string DomainName => Encoding.UTF8.GetString(DomainNameSpan);
+
+    private const int UtsLength = 64;
+
+    private const int FieldCount = 6;
+
+    private Span<byte> GetValue(int fieldIndex)
+    {
+        var startOffset = (UtsLength + 1) * fieldIndex;
+        var length = 0;
+        while (Marshal.ReadByte(_buffer, startOffset + length) != 0)
+        {
+            length++;
+        }
+
+        unsafe
+        {
+            return new Span<byte>((byte*)_buffer + startOffset, length);
+        }
+    }
+
+    [DllImport("libc")]
+    private static extern int uname(IntPtr buf);
+
+    private readonly IntPtr _buffer;
+
+    public void Dispose()
+    {
+        Marshal.FreeHGlobal(_buffer);
+    }
+}

src/Avalonia.X11/X11Window.cs

@@ -27,6 +27,7 @@
 using System.Runtime.InteropServices;
 using Avalonia.Dialogs;
 using Avalonia.Platform.Storage.FileIO;
+using System.Reflection.Metadata;
 
 // ReSharper disable IdentifierTypo
 // ReSharper disable StringLiteralTypo
@@ -343,20 +344,26 @@ private void AppendPid(IntPtr windowXId)
                 _x11.Atoms._NET_WM_PID, _x11.Atoms.XA_CARDINAL, 32,
                 PropertyMode.Replace, ref pid, 1);
 
-            // If _NET_WM_PID is set, the ICCCM-specified property WM_CLIENT_MACHINE MUST also be set. 
-            var hostNameFilePath = "cat /proc/sys/kernel/hostname";
-            if (File.Exists(hostNameFilePath))
-            {
-                var WM_CLIENT_MACHINE = XInternAtom(_x11.Display, "WM_CLIENT_MACHINE", false);
-                var hostName = File.ReadAllText(hostNameFilePath);
-                var stringToHGlobalAnsi = Marshal.StringToHGlobalAnsi(hostName);
+            // If _NET_WM_PID is set, the ICCCM-specified property WM_CLIENT_MACHINE MUST also be set.
+            // the hostname can change, so we can't cache it
+            // gethostname(3) on Linux just calls uname(2), so do it ourselves
+            // and avoid a memcpy
+            using var utsName = UtsName.GetUtsName();
+
+            var WM_CLIENT_MACHINE = XInternAtom(_x11.Display, "WM_CLIENT_MACHINE", false);
 
+            var nodeNameSpan = utsName.NodeNameSpan;
+            fixed (byte* pNodeName = &nodeNameSpan.GetPinnableReference())
+            {
                 XChangeProperty(_x11.Display, windowXId,
                     WM_CLIENT_MACHINE, _x11.Atoms.XA_STRING, 8,
-                    PropertyMode.Replace, ref stringToHGlobalAnsi, (int)hostName.Length);
+                    PropertyMode.Replace, pNodeName, nodeNameSpan.Length);
             }
         }
 
+        [DllImport("libc")]
+        static extern int uname(IntPtr buf);
+
         private static readonly int s_pid = GetProcessId();
 
         private static int GetProcessId()