System.IO.FileStream.PreOpenConfigurationFromOptions C# (CSharp) Method

        private static Interop.Sys.OpenFlags PreOpenConfigurationFromOptions(FileMode mode, FileAccess access, FileOptions options)
        {
            // Translate FileMode.  Most of the values map cleanly to one or more options for open.
            Interop.Sys.OpenFlags flags = default(Interop.Sys.OpenFlags);
            switch (mode)
            {
                default:
                case FileMode.Open: // Open maps to the default behavior for open(...).  No flags needed.
                    break;

                case FileMode.Append: // Append is the same as OpenOrCreate, except that we'll also separately jump to the end later
                case FileMode.OpenOrCreate:
                    flags |= Interop.Sys.OpenFlags.O_CREAT;
                    break;

                case FileMode.Create:
                    flags |= (Interop.Sys.OpenFlags.O_CREAT | Interop.Sys.OpenFlags.O_TRUNC);
                    break;

                case FileMode.CreateNew:
                    flags |= (Interop.Sys.OpenFlags.O_CREAT | Interop.Sys.OpenFlags.O_EXCL);
                    break;

                case FileMode.Truncate:
                    flags |= Interop.Sys.OpenFlags.O_TRUNC;
                    break;
            }

            // Translate FileAccess.  All possible values map cleanly to corresponding values for open.
            switch (access)
            {
                case FileAccess.Read:
                    flags |= Interop.Sys.OpenFlags.O_RDONLY;
                    break;

                case FileAccess.ReadWrite:
                    flags |= Interop.Sys.OpenFlags.O_RDWR;
                    break;

                case FileAccess.Write:
                    flags |= Interop.Sys.OpenFlags.O_WRONLY;
                    break;
            }

            // Translate some FileOptions; some just aren't supported, and others will be handled after calling open.
            // - Asynchronous: Handled in ctor, setting _useAsync and SafeFileHandle.IsAsync to true
            // - DeleteOnClose: Doesn't have a Unix equivalent, but we approximate it in Dispose
            // - Encrypted: No equivalent on Unix and is ignored
            // - RandomAccess: Implemented after open if posix_fadvise is available
            // - SequentialScan: Implemented after open if posix_fadvise is available
            // - WriteThrough: Handled here
            if ((options & FileOptions.WriteThrough) != 0)
            {
                flags |= Interop.Sys.OpenFlags.O_SYNC;
            }

            return flags;
        }