m_vnode
struct m_vnode vp = { fsopts, NULL };
getblk(struct m_vnode *vp, daddr_t blkno, int size, int u1 __unused,
bread(struct m_vnode *vp, daddr_t blkno, int size, struct ucred *u1 __unused,
int bread(struct m_vnode *, daddr_t, int, struct ucred *,
struct m_buf * getblk(struct m_vnode *, daddr_t, int, int, int, int);
struct m_vnode vp, rootvp;
struct m_vnode;
struct msdosfsmount *msdosfs_mount(struct m_vnode *);
int msdosfs_root(struct msdosfsmount *, struct m_vnode *);
struct msdosfsmount *m_msdosfs_mount(struct m_vnode *devvp);
msdosfs_root(struct msdosfsmount *pmp, struct m_vnode *vp) {
*vp = *(struct m_vnode *)pmp->pm_devvp;
m_msdosfs_mount(struct m_vnode *devvp)