Function getvnode

freebsd/kern/vfs_syscalls.c:4239–4267

* Convert a user file descriptor to a kernel file entry and check that, if it * is a capability, the correct rights are present. A reference on the file * entry is held upon returning. */

 * entry is held upon returning.
 */
int
getvnode(struct thread *td, int fd, cap_rights_t *rightsp, struct file **fpp)
{
	struct file *fp;
	int error;

	error = fget_unlocked(td->td_proc->p_fd, fd, rightsp, &fp);
	if (error != 0)
		return (error);

	/*
	 * The file could be not of the vnode type, or it may be not
	 * yet fully initialized, in which case the f_vnode pointer
	 * may be set, but f_ops is still badfileops.  E.g.,
	 * devfs_open() transiently create such situation to
	 * facilitate csw d_fdopen().
	 *
	 * Dupfdopen() handling in kern_openat() installs the
	 * half-baked file into the process descriptor table, allowing
	 * other thread to dereference it. Guard against the race by
	 * checking f_ops.
	 */
	if (fp->f_vnode == NULL || fp->f_ops == &badfileops) {
		fdrop(fp, td);
		return (EINVAL);
	}
	*fpp = fp;
	return (0);
}

/*
 * Get an (NFS) file handle.