Although vnode is used extensively in the operating system, it is not exposed to application programs except through a few limited means. For example, the stat program is a way to acquire inode information of a file.
Use the command man 2 stat to learn about the programming interface of stat. The key to stat is the definition of struct stat, which is contained in /usr/include/bits/stat.h. To fill a struct stat, the program stat invokes a system service. (service 18, to be exact).
This is as much information an application can collect about an inode (vnode). It is sufficient, however, to determine many important attributes of an inode, including its type.
For example, the command “stat /” reports what the root directory is.