The thread performing the call; this pointer will be dereferenced to find the process and its file descriptor structure, in order to identify the root vnode to use.
The vnode to search for; must be locked by the caller.
Pointer to a .Vt "char *" that vn_fullpath may (on success) point at a newly allocated buffer containing the resulting pathname.
Pointer to a .Vt "char *" that vn_fullpath may (on success) point at a buffer to be freed, when the caller is done with retbuf.
Typical consumers will declare two character pointers: fullpath and freepath; they will set freepath to NULL, and fullpath to a name to use in the event that the call to vn_fullpath fails. After done with the value of fullpath, the caller will check if freepath is non- NULL, and if so, invoke free(9) with a pool type of M_TEMP.