Function dounmount

freebsd/kern/vfs_mount.c:1730–1907

* Do the actual filesystem unmount. */

 * Do the actual filesystem unmount.
 */
int
dounmount(struct mount *mp, int flags, struct thread *td)
{
	struct vnode *coveredvp, *rootvp;
	int error;
	uint64_t async_flag;
	int mnt_gen_r;

	if ((coveredvp = mp->mnt_vnodecovered) != NULL) {
		mnt_gen_r = mp->mnt_gen;
		VI_LOCK(coveredvp);
		vholdl(coveredvp);
		vn_lock(coveredvp, LK_EXCLUSIVE | LK_INTERLOCK | LK_RETRY);
		/*
		 * Check for mp being unmounted while waiting for the
		 * covered vnode lock.
		 */
		if (coveredvp->v_mountedhere != mp ||
		    coveredvp->v_mountedhere->mnt_gen != mnt_gen_r) {
			VOP_UNLOCK(coveredvp);
			vdrop(coveredvp);
			vfs_rel(mp);
			return (EBUSY);
		}
	}

	/*
	 * Only privileged root, or (if MNT_USER is set) the user that did the
	 * original mount is permitted to unmount this filesystem.
	 */
	error = vfs_suser(mp, td);
	if (error != 0) {
		if (coveredvp != NULL) {
			VOP_UNLOCK(coveredvp);
			vdrop(coveredvp);
		}
		vfs_rel(mp);
		return (error);
	}

	vfs_op_enter(mp);

	vn_start_write(NULL, &mp, V_WAIT | V_MNTREF);
	MNT_ILOCK(mp);
	if ((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0 ||
	    (mp->mnt_flag & MNT_UPDATE) != 0 ||
	    !TAILQ_EMPTY(&mp->mnt_uppers)) {
		dounmount_cleanup(mp, coveredvp, 0);
		return (EBUSY);
	}
	mp->mnt_kern_flag |= MNTK_UNMOUNT;
	rootvp = vfs_cache_root_clear(mp);
	if (coveredvp != NULL)
		vn_seqc_write_begin(coveredvp);
	if (flags & MNT_NONBUSY) {
		MNT_IUNLOCK(mp);
		error = vfs_check_usecounts(mp);
		MNT_ILOCK(mp);