Xattr+Winfsp: Wrong return code if underlying FS does not support extended attributes

[infeo]

Fuse-nio-adapter version: 4.0.0-beta4

With commit 5ce3f13 fuse-nio-adapter supports extended attributes. But since backend filesystem also needs to support extended attributes by implementing the UserDefinedFileAttributeView.

In the adapter, we check if this is implemented with

fuse-nio-adapter/src/main/java/org/cryptomator/frontend/fuse/ReadOnlyAdapter.java

Lines 229 to 231 in 0066fe4

	if (xattr == null) {
	return -errno.enotsup();
	}

So far so good. Unfortunately, ENOTSUP error code is mapped in WinFSP to the NTSTATUS code STATUS_ACCESS_DENIED, leading to unexpected results. The reason is, that winfsp uses the function fsp_fuse_ntstatus_from_errno to map POSIX errors to Windows NTSTATUSes. The actual mapping is defined in errno.i and if none is found, by default ACCESS_DENIED is returned, which is here the case. (The actual value of ENOTSUP is defined in the Windows version of errno.h)

[infeo]

Actual fix depends on winfsp/winfsp#531.

For now, xattr support will be deactivated in the Winfsp mounters.

[infeo]

Closed with e53e100