[*] UNIX: Use O_EXCL if available

[*] UNIX: Try to open readable dirs

Source/IO/AuIOHandle.Unix.cpp

@@ -139,6 +139,8 @@ namespace Aurora::IO
             this->bDirectIO = true;
         }
 
+        int flags {};
+
         switch (create.eMode)
         {
         case FS::EFileOpenMode::eRead:
@@ -156,26 +158,57 @@ namespace Aurora::IO
 
             if (create.bFailIfNonEmptyFile)
             {
+            #if defined(O_EXCL)
+                flags = O_EXCL;
+            #else
                 if (AuFS::FileExists(pathex.c_str()))
                 {
                     SysPushErrorResourceExists("File {} already exists", create.path);
                     return false;
                 }
+            #endif
             }
            
             break;
         }
         };
         
+        flags |= create.eMode == FS::EFileOpenMode::eRead ? O_RDONLY : (O_RDWR | O_CREAT);
+        flags |= O_CLOEXEC;
+        flags |= this->bDirectIO ? O_DIRECT : 0;
+
         iFileDescriptor = ::open(pathex.c_str(),
-                                 (create.eMode == FS::EFileOpenMode::eRead ? O_RDONLY : (O_RDWR | O_CREAT)) | O_CLOEXEC | (this->bDirectIO ? O_DIRECT : 0),
+                                 flags,
                                  0664);
 
+        if (iFileDescriptor < 0)
+        {
+            if (errno == EEXIST)
+            {
+                SysPushErrorResourceExists("File {} already exists", create.path);
+                return false;
+            }
+
+            if (errno == EISDIR)
+            {
+                flags &= ~(O_WRONLY | O_RDWR);
+                iFileDescriptor = ::open(pathex.c_str(),
+                                         flags,
+                                         0664);
+            }
+
+            if (errno == ENFILE)
+            {
+                SysPushErrorIOResourceFailure("low resources");
+                return false;
+            }
+
             if (iFileDescriptor < 0)
             {
                 SysPushErrorIO("Couldn't open file: {} ({}) {}", path, pathex, errno);
                 return false;
             }
+        }
 
         if (!FS::ApplyDumbAdvisoryLock(iFileDescriptor, create.eAdvisoryLevel))
         {