C++ DROP_GIANT函数代码示例

static void
vfs_mountroot_wait(void)
{
	struct root_hold_token *h;
	struct timeval lastfail;
	int curfail;

	curfail = 0;
	while (1) {
		DROP_GIANT();
		g_waitidle();
		PICKUP_GIANT();
		mtx_lock(&mountlist_mtx);
		if (LIST_EMPTY(&root_holds)) {
			mtx_unlock(&mountlist_mtx);
			break;
		}
		if (ppsratecheck(&lastfail, &curfail, 1)) {
			printf("Root mount waiting for:");
			LIST_FOREACH(h, &root_holds, list)
				printf(" %s", h->who);
			printf("\n");
		}
		msleep(&root_holds, &mountlist_mtx, PZERO | PDROP, "roothold",
		    hz);
	}
}

void
uio_yield(void)
{
	struct thread *td;

	td = curthread;
	DROP_GIANT();
#ifndef __rtems__
	thread_lock(td);
	sched_prio(td, td->td_user_pri);
	mi_switch(SW_INVOL | SWT_RELINQUISH, NULL);
	thread_unlock(td);
#else /* __rtems__ */
	rtems_task_wake_after(RTEMS_YIELD_PROCESSOR);
#endif /* __rtems__ */
	PICKUP_GIANT();
}

static int
udf_unmount(struct mount *mp, int mntflags)
{
	struct udf_mnt *udfmp;
	int error, flags = 0;

	udfmp = VFSTOUDFFS(mp);

	if (mntflags & MNT_FORCE)
		flags |= FORCECLOSE;

	if ((error = vflush(mp, 0, flags, curthread)))
		return (error);

	if (udfmp->im_flags & UDFMNT_KICONV && udf_iconv) {
		if (udfmp->im_d2l)
			udf_iconv->close(udfmp->im_d2l);
#if 0
		if (udfmp->im_l2d)
			udf_iconv->close(udfmp->im_l2d);
#endif
	}

	DROP_GIANT();
	g_topology_lock();
	g_vfs_close(udfmp->im_cp);
	g_topology_unlock();
	PICKUP_GIANT();
	vrele(udfmp->im_devvp);
	dev_rel(udfmp->im_dev);

	if (udfmp->s_table != NULL)
		free(udfmp->s_table, M_UDFMOUNT);

	free(udfmp, M_UDFMOUNT);

	mp->mnt_data = NULL;
	MNT_ILOCK(mp);
	mp->mnt_flag &= ~MNT_LOCAL;
	MNT_IUNLOCK(mp);

	return (0);
}

static int
g_mbr_ioctl(struct g_provider *pp, u_long cmd, void *data, int fflag, struct thread *td)
{
	struct g_geom *gp;
	struct g_mbr_softc *ms;
	struct g_slicer *gsp;
	struct g_consumer *cp;
	int error, opened;

	gp = pp->geom;
	gsp = gp->softc;
	ms = gsp->softc;

	opened = 0;
	error = 0;
	switch(cmd) {
	case DIOCSMBR: {
		if (!(fflag & FWRITE))
			return (EPERM);
		DROP_GIANT();
		g_topology_lock();
		cp = LIST_FIRST(&gp->consumer);
		if (cp->acw == 0) {
			error = g_access(cp, 0, 1, 0);
			if (error == 0)
				opened = 1;
		}
		if (!error)
			error = g_mbr_modify(gp, ms, data, 512);
		if (!error)
			error = g_write_data(cp, 0, data, 512);
		if (opened)
			g_access(cp, 0, -1 , 0);
		g_topology_unlock();
		PICKUP_GIANT();
		return(error);
	}
	default:
		return (ENOIOCTL);
	}
}

static int
udf_mountfs(struct vnode *devvp, struct mount *mp)
{
	struct buf *bp = NULL;
	struct cdev *dev;
	struct anchor_vdp avdp;
	struct udf_mnt *udfmp = NULL;
	struct part_desc *pd;
	struct logvol_desc *lvd;
	struct fileset_desc *fsd;
	struct file_entry *root_fentry;
	uint32_t sector, size, mvds_start, mvds_end;
	uint32_t logical_secsize;
	uint32_t fsd_offset = 0;
	uint16_t part_num = 0, fsd_part = 0;
	int error = EINVAL;
	int logvol_found = 0, part_found = 0, fsd_found = 0;
	int bsize;
	struct g_consumer *cp;
	struct bufobj *bo;

	dev = devvp->v_rdev;
	dev_ref(dev);
	DROP_GIANT();
	g_topology_lock();
	error = g_vfs_open(devvp, &cp, "udf", 0);
	g_topology_unlock();
	PICKUP_GIANT();
	VOP_UNLOCK(devvp, 0);
	if (error)
		goto bail;

	bo = &devvp->v_bufobj;

	if (devvp->v_rdev->si_iosize_max != 0)
		mp->mnt_iosize_max = devvp->v_rdev->si_iosize_max;
	if (mp->mnt_iosize_max > MAXPHYS)
		mp->mnt_iosize_max = MAXPHYS;

	/* XXX: should be M_WAITOK */
	udfmp = malloc(sizeof(struct udf_mnt), M_UDFMOUNT,
	    M_NOWAIT | M_ZERO);
	if (udfmp == NULL) {
		printf("Cannot allocate UDF mount struct\n");
		error = ENOMEM;
		goto bail;
	}

	mp->mnt_data = udfmp;
	mp->mnt_stat.f_fsid.val[0] = dev2udev(devvp->v_rdev);
	mp->mnt_stat.f_fsid.val[1] = mp->mnt_vfc->vfc_typenum;
	MNT_ILOCK(mp);
	mp->mnt_flag |= MNT_LOCAL;
	mp->mnt_kern_flag |= MNTK_LOOKUP_SHARED | MNTK_EXTENDED_SHARED;
	MNT_IUNLOCK(mp);
	udfmp->im_mountp = mp;
	udfmp->im_dev = dev;
	udfmp->im_devvp = devvp;
	udfmp->im_d2l = NULL;
	udfmp->im_cp = cp;
	udfmp->im_bo = bo;

#if 0
	udfmp->im_l2d = NULL;
#endif
	/*
	 * The UDF specification defines a logical sectorsize of 2048
	 * for DVD media.
	 */
	logical_secsize = 2048;

	if (((logical_secsize % cp->provider->sectorsize) != 0) ||
	    (logical_secsize < cp->provider->sectorsize)) {
		error = EINVAL;
		goto bail;
	}

	bsize = cp->provider->sectorsize;

	/* 
	 * Get the Anchor Volume Descriptor Pointer from sector 256.
	 * XXX Should also check sector n - 256, n, and 512.
	 */
	sector = 256;
	if ((error = bread(devvp, sector * btodb(logical_secsize), bsize,
			   NOCRED, &bp)) != 0)
		goto bail;
	if ((error = udf_checktag((struct desc_tag *)bp->b_data, TAGID_ANCHOR)))
		goto bail;

	bcopy(bp->b_data, &avdp, sizeof(struct anchor_vdp));
	brelse(bp);
	bp = NULL;

	/*
	 * Extract the Partition Descriptor and Logical Volume Descriptor
	 * from the Volume Descriptor Sequence.
	 * XXX Should we care about the partition type right now?
	 * XXX What about multiple partitions?
	 */
//.........这里部分代码省略.........

/*
 * Unmount the filesystem described by mp.
 */
static int
msdosfs_unmount(struct mount *mp, int mntflags)
{
	struct msdosfsmount *pmp;
	int error, flags;

	error = flags = 0;
	pmp = VFSTOMSDOSFS(mp);
	if ((pmp->pm_flags & MSDOSFSMNT_RONLY) == 0)
		error = msdosfs_sync(mp, MNT_WAIT);
	if ((mntflags & MNT_FORCE) != 0)
		flags |= FORCECLOSE;
	else if (error != 0)
		return (error);
	error = vflush(mp, 0, flags, curthread);
	if (error != 0 && error != ENXIO)
		return (error);
	if ((pmp->pm_flags & MSDOSFSMNT_RONLY) == 0) {
		error = markvoldirty(pmp, 0);
		if (error && error != ENXIO) {
			(void)markvoldirty(pmp, 1);
			return (error);
		}
	}
	if (pmp->pm_flags & MSDOSFSMNT_KICONV && msdosfs_iconv) {
		if (pmp->pm_w2u)
			msdosfs_iconv->close(pmp->pm_w2u);
		if (pmp->pm_u2w)
			msdosfs_iconv->close(pmp->pm_u2w);
		if (pmp->pm_d2u)
			msdosfs_iconv->close(pmp->pm_d2u);
		if (pmp->pm_u2d)
			msdosfs_iconv->close(pmp->pm_u2d);
	}

#ifdef MSDOSFS_DEBUG
	{
		struct vnode *vp = pmp->pm_devvp;
		struct bufobj *bo;

		bo = &vp->v_bufobj;
		BO_LOCK(bo);
		VI_LOCK(vp);
		vn_printf(vp,
		    "msdosfs_umount(): just before calling VOP_CLOSE()\n");
		printf("freef %p, freeb %p, mount %p\n",
		    TAILQ_NEXT(vp, v_actfreelist), vp->v_actfreelist.tqe_prev,
		    vp->v_mount);
		printf("cleanblkhd %p, dirtyblkhd %p, numoutput %ld, type %d\n",
		    TAILQ_FIRST(&vp->v_bufobj.bo_clean.bv_hd),
		    TAILQ_FIRST(&vp->v_bufobj.bo_dirty.bv_hd),
		    vp->v_bufobj.bo_numoutput, vp->v_type);
		VI_UNLOCK(vp);
		BO_UNLOCK(bo);
	}
#endif
	DROP_GIANT();
	if (pmp->pm_devvp->v_type == VCHR && pmp->pm_devvp->v_rdev != NULL)
		pmp->pm_devvp->v_rdev->si_mountpt = NULL;
	g_topology_lock();
	g_vfs_close(pmp->pm_cp);
	g_topology_unlock();
	PICKUP_GIANT();
	vrele(pmp->pm_devvp);
	dev_rel(pmp->pm_dev);
	free(pmp->pm_inusemap, M_MSDOSFSFAT);
	if (pmp->pm_flags & MSDOSFS_LARGEFS)
		msdosfs_fileno_free(mp);
	lockdestroy(&pmp->pm_fatlock);
	free(pmp, M_MSDOSFSMNT);
	mp->mnt_data = NULL;
	MNT_ILOCK(mp);
	mp->mnt_flag &= ~MNT_LOCAL;
	MNT_IUNLOCK(mp);
	return (error);
}

static int
mountmsdosfs(struct vnode *devvp, struct mount *mp)
{
	struct msdosfsmount *pmp;
	struct buf *bp;
	struct cdev *dev;
	union bootsector *bsp;
	struct byte_bpb33 *b33;
	struct byte_bpb50 *b50;
	struct byte_bpb710 *b710;
	u_int8_t SecPerClust;
	u_long clusters;
	int ronly, error;
	struct g_consumer *cp;
	struct bufobj *bo;

	bp = NULL;		/* This and pmp both used in error_exit. */
	pmp = NULL;
	ronly = (mp->mnt_flag & MNT_RDONLY) != 0;

	dev = devvp->v_rdev;
	dev_ref(dev);
	DROP_GIANT();
	g_topology_lock();
	error = g_vfs_open(devvp, &cp, "msdosfs", ronly ? 0 : 1);
	g_topology_unlock();
	PICKUP_GIANT();
	VOP_UNLOCK(devvp, 0);
	if (error)
		goto error_exit;

	bo = &devvp->v_bufobj;

	/*
	 * Read the boot sector of the filesystem, and then check the
	 * boot signature.  If not a dos boot sector then error out.
	 *
	 * NOTE: 8192 is a magic size that works for ffs.
	 */
	error = bread(devvp, 0, 8192, NOCRED, &bp);
	if (error)
		goto error_exit;
	bp->b_flags |= B_AGE;
	bsp = (union bootsector *)bp->b_data;
	b33 = (struct byte_bpb33 *)bsp->bs33.bsBPB;
	b50 = (struct byte_bpb50 *)bsp->bs50.bsBPB;
	b710 = (struct byte_bpb710 *)bsp->bs710.bsBPB;

#ifndef MSDOSFS_NOCHECKSIG
	if (bsp->bs50.bsBootSectSig0 != BOOTSIG0
	    || bsp->bs50.bsBootSectSig1 != BOOTSIG1) {
		error = EINVAL;
		goto error_exit;
	}
#endif

	pmp = malloc(sizeof *pmp, M_MSDOSFSMNT, M_WAITOK | M_ZERO);
	pmp->pm_mountp = mp;
	pmp->pm_cp = cp;
	pmp->pm_bo = bo;

	lockinit(&pmp->pm_fatlock, 0, msdosfs_lock_msg, 0, 0);

	/*
	 * Initialize ownerships and permissions, since nothing else will
	 * initialize them iff we are mounting root.
	 */
	pmp->pm_uid = UID_ROOT;
	pmp->pm_gid = GID_WHEEL;
	pmp->pm_mask = pmp->pm_dirmask = S_IXUSR | S_IXGRP | S_IXOTH |
	    S_IRUSR | S_IRGRP | S_IROTH | S_IWUSR;

	/*
	 * Experimental support for large MS-DOS filesystems.
	 * WARNING: This uses at least 32 bytes of kernel memory (which is not
	 * reclaimed until the FS is unmounted) for each file on disk to map
	 * between the 32-bit inode numbers used by VFS and the 64-bit
	 * pseudo-inode numbers used internally by msdosfs. This is only
	 * safe to use in certain controlled situations (e.g. read-only FS
	 * with less than 1 million files).
	 * Since the mappings do not persist across unmounts (or reboots), these
	 * filesystems are not suitable for exporting through NFS, or any other
	 * application that requires fixed inode numbers.
	 */
	vfs_flagopt(mp->mnt_optnew, "large", &pmp->pm_flags, MSDOSFS_LARGEFS);

	/*
	 * Compute several useful quantities from the bpb in the
	 * bootsector.  Copy in the dos 5 variant of the bpb then fix up
	 * the fields that are different between dos 5 and dos 3.3.
	 */
	SecPerClust = b50->bpbSecPerClust;
	pmp->pm_BytesPerSec = getushort(b50->bpbBytesPerSec);
	if (pmp->pm_BytesPerSec < DEV_BSIZE) {
		error = EINVAL;
		goto error_exit;
	}
	pmp->pm_ResSectors = getushort(b50->bpbResSectors);
	pmp->pm_FATs = b50->bpbFATs;
	pmp->pm_RootDirEnts = getushort(b50->bpbRootDirEnts);
//.........这里部分代码省略.........

/*
 * mp - path - addr in user space of mount point (ie /usr or whatever)
 * data - addr in user space of mount params including the name of the block
 * special file to treat as a filesystem.
 */
static int
msdosfs_mount(struct mount *mp)
{
	struct vnode *devvp;	  /* vnode for blk device to mount */
	struct thread *td;
	/* msdosfs specific mount control block */
	struct msdosfsmount *pmp = NULL;
	struct nameidata ndp;
	int error, flags;
	accmode_t accmode;
	char *from;

	td = curthread;
	if (vfs_filteropt(mp->mnt_optnew, msdosfs_opts))
		return (EINVAL);

	/*
	 * If updating, check whether changing from read-only to
	 * read/write; if there is no device name, that's all we do.
	 */
	if (mp->mnt_flag & MNT_UPDATE) {
		pmp = VFSTOMSDOSFS(mp);
		if (vfs_flagopt(mp->mnt_optnew, "export", NULL, 0)) {
			/*
			 * Forbid export requests if filesystem has
			 * MSDOSFS_LARGEFS flag set.
			 */
			if ((pmp->pm_flags & MSDOSFS_LARGEFS) != 0) {
				vfs_mount_error(mp,
				    "MSDOSFS_LARGEFS flag set, cannot export");
				return (EOPNOTSUPP);
			}
		}
		if (!(pmp->pm_flags & MSDOSFSMNT_RONLY) &&
		    vfs_flagopt(mp->mnt_optnew, "ro", NULL, 0)) {
			error = VFS_SYNC(mp, MNT_WAIT);
			if (error)
				return (error);
			flags = WRITECLOSE;
			if (mp->mnt_flag & MNT_FORCE)
				flags |= FORCECLOSE;
			error = vflush(mp, 0, flags, td);
			if (error)
				return (error);

			/*
			 * Now the volume is clean.  Mark it so while the
			 * device is still rw.
			 */
			error = markvoldirty(pmp, 0);
			if (error) {
				(void)markvoldirty(pmp, 1);
				return (error);
			}

			/* Downgrade the device from rw to ro. */
			DROP_GIANT();
			g_topology_lock();
			error = g_access(pmp->pm_cp, 0, -1, 0);
			g_topology_unlock();
			PICKUP_GIANT();
			if (error) {
				(void)markvoldirty(pmp, 1);
				return (error);
			}

			/*
			 * Backing out after an error was painful in the
			 * above.  Now we are committed to succeeding.
			 */
			pmp->pm_fmod = 0;
			pmp->pm_flags |= MSDOSFSMNT_RONLY;
			MNT_ILOCK(mp);
			mp->mnt_flag |= MNT_RDONLY;
			MNT_IUNLOCK(mp);
		} else if ((pmp->pm_flags & MSDOSFSMNT_RONLY) &&
		    !vfs_flagopt(mp->mnt_optnew, "ro", NULL, 0)) {
			/*
			 * If upgrade to read-write by non-root, then verify
			 * that user has necessary permissions on the device.
			 */
			devvp = pmp->pm_devvp;
			vn_lock(devvp, LK_EXCLUSIVE | LK_RETRY);
			error = VOP_ACCESS(devvp, VREAD | VWRITE,
			    td->td_ucred, td);
			if (error)
				error = priv_check(td, PRIV_VFS_MOUNT_PERM);
			if (error) {
				VOP_UNLOCK(devvp, 0);
				return (error);
			}
			VOP_UNLOCK(devvp, 0);
			DROP_GIANT();
			g_topology_lock();
			error = g_access(pmp->pm_cp, 0, 1, 0);
//.........这里部分代码省略.........

/*-
 * This start routine is only called for non-trivial requests, all the
 * trivial ones are handled autonomously by the slice code.
 * For requests we handle here, we must call the g_io_deliver() on the
 * bio, and return non-zero to indicate to the slice code that we did so.
 * This code executes in the "DOWN" I/O path, this means:
 *    * No sleeping.
 *    * Don't grab the topology lock.
 *    * Don't call biowait, g_getattr(), g_setattr() or g_read_data()
 */
static int
g_bsd_ioctl(struct g_provider *pp, u_long cmd, void *data, int fflag, struct thread *td)
{
	struct g_geom *gp;
	struct g_bsd_softc *ms;
	struct g_slicer *gsp;
	u_char *label;
	int error;

	gp = pp->geom;
	gsp = gp->softc;
	ms = gsp->softc;

	switch(cmd) {
	case DIOCGDINFO:
		/* Return a copy of the disklabel to userland. */
		bsd_disklabel_le_dec(ms->label, data, MAXPARTITIONS);
		return(0);
	case DIOCBSDBB: {
		struct g_consumer *cp;
		u_char *buf;
		void *p;
		int error, i;
		uint64_t sum;

		if (!(fflag & FWRITE))
			return (EPERM);
		/* The disklabel to set is the ioctl argument. */
		buf = g_malloc(BBSIZE, M_WAITOK);
		p = *(void **)data;
		error = copyin(p, buf, BBSIZE);
		if (!error) {
			/* XXX: Rude, but supposedly safe */
			DROP_GIANT();
			g_topology_lock();
			/* Validate and modify our slice instance to match. */
			error = g_bsd_modify(gp, buf + ms->labeloffset);
			if (!error) {
				cp = LIST_FIRST(&gp->consumer);
				if (ms->labeloffset == ALPHA_LABEL_OFFSET) {
					sum = 0;
					for (i = 0; i < 63; i++)
						sum += le64dec(buf + i * 8);
					le64enc(buf + 504, sum);
				}
				error = g_write_data(cp, 0, buf, BBSIZE);
			}
			g_topology_unlock();
			PICKUP_GIANT();
		}
		g_free(buf);
		return (error);
	}
	case DIOCSDINFO:
	case DIOCWDINFO: {
		if (!(fflag & FWRITE))
			return (EPERM);
		label = g_malloc(LABELSIZE, M_WAITOK);
		/* The disklabel to set is the ioctl argument. */
		bsd_disklabel_le_enc(label, data);

		DROP_GIANT();
		g_topology_lock();
		/* Validate and modify our slice instance to match. */
		error = g_bsd_modify(gp, label);
		if (error == 0 && cmd == DIOCWDINFO)
			error = g_bsd_writelabel(gp, NULL);
		g_topology_unlock();
		PICKUP_GIANT();
		g_free(label);
		return(error);
	}
	default:
		return (ENOIOCTL);
	}
}

static int
parse_dir_md(char **conf)
{
	struct stat sb;
	struct thread *td;
	struct md_ioctl *mdio;
	char *path, *tok;
	int error, fd, len;

	td = curthread;

	error = parse_token(conf, &tok);
	if (error)
		return (error);

	len = strlen(tok);
	mdio = malloc(sizeof(*mdio) + len + 1, M_TEMP, M_WAITOK | M_ZERO);
	path = (void *)(mdio + 1);
	bcopy(tok, path, len);
	free(tok, M_TEMP);

	/* Get file status. */
	error = kern_stat(td, path, UIO_SYSSPACE, &sb);
	if (error)
		goto out;

	/* Open /dev/mdctl so that we can attach/detach. */
	error = kern_open(td, "/dev/" MDCTL_NAME, UIO_SYSSPACE, O_RDWR, 0);
	if (error)
		goto out;

	fd = td->td_retval[0];
	mdio->md_version = MDIOVERSION;
	mdio->md_type = MD_VNODE;

	if (root_mount_mddev != -1) {
		mdio->md_unit = root_mount_mddev;
		DROP_GIANT();
		error = kern_ioctl(td, fd, MDIOCDETACH, (void *)mdio);
		PICKUP_GIANT();
		/* Ignore errors. We don't care. */
		root_mount_mddev = -1;
	}

	mdio->md_file = (void *)(mdio + 1);
	mdio->md_options = MD_AUTOUNIT | MD_READONLY;
	mdio->md_mediasize = sb.st_size;
	mdio->md_unit = 0;
	DROP_GIANT();
	error = kern_ioctl(td, fd, MDIOCATTACH, (void *)mdio);
	PICKUP_GIANT();
	if (error)
		goto out;

	if (mdio->md_unit > 9) {
		printf("rootmount: too many md units\n");
		mdio->md_file = NULL;
		mdio->md_options = 0;
		mdio->md_mediasize = 0;
		DROP_GIANT();
		error = kern_ioctl(td, fd, MDIOCDETACH, (void *)mdio);
		PICKUP_GIANT();
		/* Ignore errors. We don't care. */
		error = ERANGE;
		goto out;
	}

	root_mount_mddev = mdio->md_unit;
	printf(MD_NAME "%u attached to %s\n", root_mount_mddev, mdio->md_file);

	error = kern_close(td, fd);

 out:
	free(mdio, M_TEMP);
	return (error);
}

/*
 * Shutdown the system cleanly to prepare for reboot, halt, or power off.
 */
void
kern_reboot(int howto)
{
	static int first_buf_printf = 1;

#if defined(SMP)
	/*
	 * Bind us to CPU 0 so that all shutdown code runs there.  Some
	 * systems don't shutdown properly (i.e., ACPI power off) if we
	 * run on another processor.
	 */
	if (!SCHEDULER_STOPPED()) {
		thread_lock(curthread);
		sched_bind(curthread, 0);
		thread_unlock(curthread);
		KASSERT(PCPU_GET(cpuid) == 0, ("boot: not running on cpu 0"));
	}
#endif
	/* We're in the process of rebooting. */
	rebooting = 1;

	/* collect extra flags that shutdown_nice might have set */
	howto |= shutdown_howto;

	/* We are out of the debugger now. */
	kdb_active = 0;

	/*
	 * Do any callouts that should be done BEFORE syncing the filesystems.
	 */
	EVENTHANDLER_INVOKE(shutdown_pre_sync, howto);

	/* 
	 * Now sync filesystems
	 */
	if (!cold && (howto & RB_NOSYNC) == 0 && waittime < 0) {
		register struct buf *bp;
		int iter, nbusy, pbusy;
#ifndef PREEMPTION
		int subiter;
#endif

		waittime = 0;

		wdog_kern_pat(WD_LASTVAL);
		sys_sync(curthread, NULL);

		/*
		 * With soft updates, some buffers that are
		 * written will be remarked as dirty until other
		 * buffers are written.
		 */
		for (iter = pbusy = 0; iter < 20; iter++) {
			nbusy = 0;
			for (bp = &buf[nbuf]; --bp >= buf; )
				if (isbufbusy(bp))
					nbusy++;
			if (nbusy == 0) {
				if (first_buf_printf)
					printf("All buffers synced.");
				break;
			}
			if (first_buf_printf) {
				printf("Syncing disks, buffers remaining... ");
				first_buf_printf = 0;
			}
			printf("%d ", nbusy);
			if (nbusy < pbusy)
				iter = 0;
			pbusy = nbusy;

			wdog_kern_pat(WD_LASTVAL);
			sys_sync(curthread, NULL);

#ifdef PREEMPTION
			/*
			 * Drop Giant and spin for a while to allow
			 * interrupt threads to run.
			 */
			DROP_GIANT();
			DELAY(50000 * iter);
			PICKUP_GIANT();
#else
			/*
			 * Drop Giant and context switch several times to
			 * allow interrupt threads to run.
			 */
			DROP_GIANT();
			for (subiter = 0; subiter < 50 * iter; subiter++) {
				thread_lock(curthread);
				mi_switch(SW_VOL, NULL);
				thread_unlock(curthread);
				DELAY(1000);
			}
			PICKUP_GIANT();
#endif
		}
//.........这里部分代码省略.........

/*ARGSUSED*/
static int
zfs_mount(vfs_t *vfsp)
{
	kthread_t	*td = curthread;
	vnode_t		*mvp = vfsp->mnt_vnodecovered;
	cred_t		*cr = td->td_ucred;
	char		*osname;
	int		error = 0;
	int		canwrite;

	if (vfs_getopt(vfsp->mnt_optnew, "from", (void **)&osname, NULL))
		return (EINVAL);

	/*
	 * If full-owner-access is enabled and delegated administration is
	 * turned on, we must set nosuid.
	 */
	if (zfs_super_owner &&
	    dsl_deleg_access(osname, ZFS_DELEG_PERM_MOUNT, cr) != ECANCELED) {
		secpolicy_fs_mount_clearopts(cr, vfsp);
	}

	/*
	 * Check for mount privilege?
	 *
	 * If we don't have privilege then see if
	 * we have local permission to allow it
	 */
	error = secpolicy_fs_mount(cr, mvp, vfsp);
	if (error) {
		error = dsl_deleg_access(osname, ZFS_DELEG_PERM_MOUNT, cr);
		if (error != 0)
			goto out;

		if (!(vfsp->vfs_flag & MS_REMOUNT)) {
			vattr_t		vattr;

			/*
			 * Make sure user is the owner of the mount point
			 * or has sufficient privileges.
			 */

			vattr.va_mask = AT_UID;

			vn_lock(mvp, LK_SHARED | LK_RETRY);
			if (error = VOP_GETATTR(mvp, &vattr, cr)) {
				VOP_UNLOCK(mvp, 0);
				goto out;
			}

#if 0 /* CHECK THIS! Is probably needed for zfs_suser. */
			if (secpolicy_vnode_owner(mvp, cr, vattr.va_uid) != 0 &&
			    VOP_ACCESS(mvp, VWRITE, cr, td) != 0) {
				error = EPERM;
				goto out;
			}
#else
			if (error = secpolicy_vnode_owner(mvp, cr, vattr.va_uid)) {
				VOP_UNLOCK(mvp, 0);
				goto out;
			}

			if (error = VOP_ACCESS(mvp, VWRITE, cr, td)) {
				VOP_UNLOCK(mvp, 0);
				goto out;
			}
			VOP_UNLOCK(mvp, 0);
#endif
		}

		secpolicy_fs_mount_clearopts(cr, vfsp);
	}

	/*
	 * Refuse to mount a filesystem if we are in a local zone and the
	 * dataset is not visible.
	 */
	if (!INGLOBALZONE(curthread) &&
	    (!zone_dataset_visible(osname, &canwrite) || !canwrite)) {
		error = EPERM;
		goto out;
	}

	/*
	 * When doing a remount, we simply refresh our temporary properties
	 * according to those options set in the current VFS options.
	 */
	if (vfsp->vfs_flag & MS_REMOUNT) {
		/* refresh mount options */
		zfs_unregister_callbacks(vfsp->vfs_data);
		error = zfs_register_callbacks(vfsp);
		goto out;
	}

	DROP_GIANT();
	error = zfs_domount(vfsp, osname);
	PICKUP_GIANT();
out:
	return (error);
//.........这里部分代码省略.........