fstat fails on mounted memory filesystem

[lambdageek]

If I create /pipe/input on the memory file system, calling int fd = open("/pipe/input", O_RDONLY); will succeed, but calling fstat(fd, &stat) will fail with EPERM

			const memFS = await wasm.createMemoryFileSystem();
			const rootFileSystem = await wasm.createRootFileSystem([
				{ kind: 'workspaceFolder' },
				{
					kind: 'memoryFileSystem',
					mountPoint: '/pipe',
					fileSystem: memFS
				},
			]);
			const pipeIn = memFS.createWritable('./input', 'utf-8');
			const seedBuf = new Uint8Array(1);
			seedBuf[0] = 42;
			pipeIn.write(seedBuf);

Repro: clone the "memfs" branch of https://github.com/lambdageek/big-buffer-write/tree/memfs build and run the extension and run it with "wasi: write big buffer". pick a small value from the Quick Pick, like 20.

Note the output in the output window:

2023-08-02 14:17:10.506 [error] stderr: the mode for /pipe is 040000

2023-08-02 14:17:10.506 [error] stderr: fstat input
2023-08-02 14:17:10.506 [error] stderr: :
2023-08-02 14:17:10.507 [error] stderr:  
2023-08-02 14:17:10.507 [error] stderr: Operation not permitted
2023-08-02 14:17:10.507 [error] stderr: 

2023-08-02 14:17:10.507 [error] stderr: that's EPERM

2023-08-02 14:17:10.509 [info] process terminated with exit code 1

---

Also, FileOnlyBaseRights looks like a typo:

vscode-wasm/wasm-wasi-core/src/common/memoryFileSystemDriver.ts

Lines 241 to 242 in 62adc93

	const DirectoryOnlyBaseRights: rights = DirectoryBaseRights & ~FileBaseRights;
	const FileOnlyBaseRights: rights = FileBaseRights & DirectoryBaseRights;

This should probably be const FileOnlyBaseRights: rights = FileBaseRights & ~DirectoryBaseRights;

---

Why I care: .NET does an FStatCheckIO after opening a file that ends up failing
https://github.com/dotnet/runtime/blob/e2a2bfff005ea0620cf1d2b04a01dc90bbfe8ead/src/libraries/System.Private.CoreLib/src/Microsoft/Win32/SafeHandles/SafeFileHandle.Unix.cs#L334

So FileStream f = File.OpenRead("/pipe/input") always fails