dirReadLinkPosix

fn dirReadLinkPosix(dir: Dir, sub_path: []const u8, buffer: []u8) Dir.ReadLinkError!usize {
    var sub_path_buffer: [posix.PATH_MAX]u8 = undefined;
    const sub_path_posix = try pathToPosix(sub_path, &sub_path_buffer);

    const syscall: Syscall = try .start();
    while (true) {
        const rc = posix.system.readlinkat(dir.handle, sub_path_posix, buffer.ptr, buffer.len);
        switch (posix.errno(rc)) {
            .SUCCESS => {
                syscall.finish();
                const len: usize = @bitCast(rc);
                return len;
            },
            .INTR => {
                try syscall.checkCancel();
                continue;
            },
            else => |e| {
                syscall.finish();
                switch (e) {
                    .ACCES => return error.AccessDenied,
                    .FAULT => |err| return errnoBug(err),
                    .INVAL => return error.NotLink,
                    .IO => return error.FileSystem,
                    .LOOP => return error.SymLinkLoop,
                    .NAMETOOLONG => return error.NameTooLong,
                    .NOENT => return error.FileNotFound,
                    .NOMEM => return error.SystemResources,
                    .NOTDIR => return error.NotDir,
                    .ILSEQ => return error.BadPathName,
                    else => |err| return posix.unexpectedErrno(err),
                }
            },
        }
    }
}