static int proc_get_sb(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
	int err;
	struct super_block *sb;
	struct pid_namespace *ns;
	struct proc_inode *ei;
	char *options;

	if (proc_mnt) {
		/* Seed the root directory with a pid so it doesn't need
		 * to be special in base.c.  I would do this earlier but
		 * the only task alive when /proc is mounted the first time
		 * is the init_task and it doesn't have any pids.
		 */
		ei = PROC_I(proc_mnt->mnt_sb->s_root->d_inode);
		if (!ei->pid)
			ei->pid = find_get_pid(1);
	}

	if (flags & MS_KERNMOUNT) {
		ns = (struct pid_namespace *)data;
		options = NULL;
	} else {
		ns = task_active_pid_ns(current);
		options = data;
	}

	sb = sget(fs_type, proc_test_super, proc_set_super, ns);
	if (IS_ERR(sb))
		return PTR_ERR(sb);

	if (!sb->s_root) {
		sb->s_flags = flags;
		if (!proc_parse_options(options, ns)) {
			deactivate_locked_super(sb);
			return -EINVAL;
		}
		err = proc_fill_super(sb);
		if (err) {
			deactivate_locked_super(sb);
			return err;
		}

		ei = PROC_I(sb->s_root->d_inode);
		if (!ei->pid) {
			rcu_read_lock();
			ei->pid = get_pid(find_pid_ns(1, ns));
			rcu_read_unlock();
		}

		sb->s_flags |= MS_ACTIVE;
		ns->proc_mnt = mnt;
	}

	simple_set_mnt(mnt, sb);
	return 0;
}

/**
 * kernfs_mount_ns - kernfs mount helper
 * @fs_type: file_system_type of the fs being mounted
 * @flags: mount flags specified for the mount
 * @root: kernfs_root of the hierarchy being mounted
 * @new_sb_created: tell the caller if we allocated a new superblock
 * @ns: optional namespace tag of the mount
 *
 * This is to be called from each kernfs user's file_system_type->mount()
 * implementation, which should pass through the specified @fs_type and
 * @flags, and specify the hierarchy and namespace tag to mount via @root
 * and @ns, respectively.
 *
 * The return value can be passed to the vfs layer verbatim.
 */
struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
			       struct kernfs_root *root, bool *new_sb_created,
			       const void *ns)
{
	struct super_block *sb;
	struct kernfs_super_info *info;
	int error;

	info = kzalloc(sizeof(*info), GFP_KERNEL);
	if (!info)
		return ERR_PTR(-ENOMEM);

	info->root = root;
	info->ns = ns;

	sb = sget(fs_type, kernfs_test_super, kernfs_set_super, flags, info);
	if (IS_ERR(sb) || sb->s_fs_info != info)
		kfree(info);
	if (IS_ERR(sb))
		return ERR_CAST(sb);

	if (new_sb_created)
		*new_sb_created = !sb->s_root;

	if (!sb->s_root) {
		error = kernfs_fill_super(sb);
		if (error) {
			deactivate_locked_super(sb);
			return ERR_PTR(error);
		}
		sb->s_flags |= MS_ACTIVE;
	}

	return dget(sb->s_root);
}

static struct dentry *sysfs_mount(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data)
{
	struct sysfs_super_info *info;
	enum kobj_ns_type type;
	struct super_block *sb;
	int error;

	info = kzalloc(sizeof(*info), GFP_KERNEL);
	if (!info)
		return ERR_PTR(-ENOMEM);

	for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++)
		info->ns[type] = kobj_ns_grab_current(type);

	sb = sget(fs_type, sysfs_test_super, sysfs_set_super, info);
	if (IS_ERR(sb) || sb->s_fs_info != info)
		free_sysfs_super_info(info);
	if (IS_ERR(sb))
		return ERR_CAST(sb);
	if (!sb->s_root) {
		sb->s_flags = flags;
		error = sysfs_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
		if (error) {
			deactivate_locked_super(sb);
			return ERR_PTR(error);
		}
		sb->s_flags |= MS_ACTIVE;
	}

	return dget(sb->s_root);
}

struct dentry *
vnlayer_mount(
    struct file_system_type *fs_type,
    int flags,
    const char *dev_name,
    void *data
)
{
    SUPER_T *sb;
    int err;

#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,6,0)
    sb = sget(fs_type, NULL, vnlayer_set_sb, flags, data);
#else
    sb = sget(fs_type, NULL, vnlayer_set_sb, data);
#endif /* LINUX_VERSION_CODE >= KERNEL_VERSION(3,6,0) */
    if (IS_ERR(sb)) {
        return (struct dentry *)(sb);
    }
    sb->s_flags = flags;
    if (sb->s_root == NULL) {
        err = vnlayer_fill_super(sb, data, 0);
        if (err != 0) {
            deactivate_locked_super(sb);
            return ERR_PTR(err);
        }
        sb->s_flags |= MS_ACTIVE;
    }
    /* return a dget dentry */
    return dget(sb->s_root);
}

void fc_drop_locked(struct fs_context *fc)
{
	struct super_block *sb = fc->root->d_sb;
	dput(fc->root);
	fc->root = NULL;
	deactivate_locked_super(sb);
}

static struct dentry *proc_mount(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data)
{
	int err;
	struct super_block *sb;
	struct pid_namespace *ns;
	struct proc_inode *ei;
	char *options;

	if (flags & MS_KERNMOUNT) {
		ns = (struct pid_namespace *)data;
		options = NULL;
	} else {
		ns = current->nsproxy->pid_ns;
		options = data;
	}

	sb = sget(fs_type, proc_test_super, proc_set_super, ns);
	if (IS_ERR(sb))
		return ERR_CAST(sb);

	if (!proc_parse_options(options, ns)) {
		deactivate_locked_super(sb);
		return ERR_PTR(-EINVAL);
	}

	if (!sb->s_root) {
		sb->s_flags = flags;
		err = proc_fill_super(sb);
		if (err) {
			deactivate_locked_super(sb);
			return ERR_PTR(err);
		}

		sb->s_flags |= MS_ACTIVE;
	}

	ei = PROC_I(sb->s_root->d_inode);
	if (!ei->pid) {
		rcu_read_lock();
		ei->pid = get_pid(find_pid_ns(1, ns));
		rcu_read_unlock();
	}

	return dget(sb->s_root);
}

static struct dentry *proc_mount(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data)
{
	int err;
	struct super_block *sb;
	struct pid_namespace *ns;
	char *options;

	if (flags & MS_KERNMOUNT) {
		ns = (struct pid_namespace *)data;
		options = NULL;
	} else {
		ns = task_active_pid_ns(current);
		options = data;

		if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
			return ERR_PTR(-EPERM);

		/* Does the mounter have privilege over the pid namespace? */
		if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
			return ERR_PTR(-EPERM);
	}

	sb = sget(fs_type, proc_test_super, proc_set_super, flags, ns);
	if (IS_ERR(sb))
		return ERR_CAST(sb);

	if (!proc_parse_options(options, ns)) {
		deactivate_locked_super(sb);
		return ERR_PTR(-EINVAL);
	}

	if (!sb->s_root) {
		err = proc_fill_super(sb);
		if (err) {
			deactivate_locked_super(sb);
			return ERR_PTR(err);
		}

		sb->s_flags |= MS_ACTIVE;
	}

	return dget(sb->s_root);
}

static struct dentry *plgfs_mount(struct file_system_type *fs_type, int flags,
		const char *dev_name, void *data_page)
{
	struct super_block *sb;
	struct plgfs_mnt_cfg *cfg;
	int rv;

	cfg = plgfs_get_cfg(fs_type, flags, dev_name, data_page);
	if (IS_ERR(cfg))
		return ERR_CAST(cfg);

	sb = sget(fs_type, plgfs_test_super, set_anon_super, flags, cfg);
	if (IS_ERR(sb)) {
		plgfs_put_cfg(cfg);
		return ERR_CAST(sb);
	}

	if (cfg->flags & PLGFS_OPT_DIFF_PLGS) {
		pr_err("pluginfs: \"%s\" already mounted with different set of "
				"plugins\n", dev_name);
		deactivate_locked_super(sb);
		plgfs_put_cfg(cfg);
		return ERR_PTR(-EINVAL);
	}

	if (sb->s_root) {
		plgfs_put_cfg(cfg);
		return dget(sb->s_root); 
	}

	rv = plgfs_fill_super(sb, flags, cfg);
	if (rv) {
		deactivate_locked_super(sb);
		plgfs_put_cfg(cfg);
		return ERR_PTR(rv);
	}

	plgfs_put_cfg(cfg);

	return dget(sb->s_root); 
}

static struct dentry *proc_mount(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data)
{
	int err;
	struct super_block *sb;
	struct pid_namespace *ns;
	char *options;

	if (flags & MS_KERNMOUNT) {
		ns = (struct pid_namespace *)data;
		options = NULL;
	} else {
		ns = task_active_pid_ns(current);
		options = data;

		if (!current_user_ns()->may_mount_proc)
			return ERR_PTR(-EPERM);
	}

	sb = sget(fs_type, proc_test_super, proc_set_super, flags, ns);
	if (IS_ERR(sb))
		return ERR_CAST(sb);

	if (!proc_parse_options(options, ns)) {
		deactivate_locked_super(sb);
		return ERR_PTR(-EINVAL);
	}

	if (!sb->s_root) {
		err = proc_fill_super(sb);
		if (err) {
			deactivate_locked_super(sb);
			return ERR_PTR(err);
		}

		sb->s_flags |= MS_ACTIVE;
	}

	return dget(sb->s_root);
}

/*
 * Get an AFS superblock and root directory.
 */
static int afs_get_tree(struct fs_context *fc)
{
	struct afs_fs_context *ctx = fc->fs_private;
	struct super_block *sb;
	struct afs_super_info *as;
	int ret;

	ret = afs_validate_fc(fc);
	if (ret)
		goto error;

	_enter("");

	/* allocate a superblock info record */
	ret = -ENOMEM;
	as = afs_alloc_sbi(fc);
	if (!as)
		goto error;
	fc->s_fs_info = as;

	/* allocate a deviceless superblock */
	sb = sget_fc(fc,
		     as->dyn_root ? afs_dynroot_test_super : afs_test_super,
		     afs_set_super);
	if (IS_ERR(sb)) {
		ret = PTR_ERR(sb);
		goto error;
	}

	if (!sb->s_root) {
		/* initial superblock/root creation */
		_debug("create");
		ret = afs_fill_super(sb, ctx);
		if (ret < 0)
			goto error_sb;
		sb->s_flags |= SB_ACTIVE;
	} else {
		_debug("reuse");
		ASSERTCMP(sb->s_flags, &, SB_ACTIVE);
	}

	fc->root = dget(sb->s_root);
	trace_afs_get_tree(as->cell, as->volume);
	_leave(" = 0 [%p]", sb);
	return 0;

error_sb:
	deactivate_locked_super(sb);
error:
	_leave(" = %d", ret);
	return ret;
}

/*
 * get a superblock on an MTD-backed filesystem
 */
static int get_sb_mtd_aux(struct file_system_type *fs_type, int flags,
			  const char *dev_name, void *data,
			  struct mtd_info *mtd,
			  int (*fill_super)(struct super_block *, void *, int),
			  struct vfsmount *mnt)
{
	struct super_block *sb;
	int ret;

	sb = sget(fs_type, get_sb_mtd_compare, get_sb_mtd_set, mtd);
	if (IS_ERR(sb))
		goto out_error;

	if (sb->s_root)
		goto already_mounted;

	/* fresh new superblock */
	DEBUG(1, "MTDSB: New superblock for device %d (\"%s\")\n",
	      mtd->index, mtd->name);

	sb->s_flags = flags;

	ret = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
	if (ret < 0) {
		deactivate_locked_super(sb);
		return ret;
	}

	/* go */
	sb->s_flags |= MS_ACTIVE;
	simple_set_mnt(mnt, sb);

	return 0;

	/* new mountpoint for an already mounted superblock */
already_mounted:
	DEBUG(1, "MTDSB: Device %d (\"%s\") is already mounted\n",
	      mtd->index, mtd->name);
	simple_set_mnt(mnt, sb);
	ret = 0;
	goto out_put;

out_error:
	ret = PTR_ERR(sb);
out_put:
	put_mtd_device(mtd);
	return ret;
}

static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
				int flags, const char *dev_name, void *data)
{
	struct dentry *root;
	root = mount_pseudo(fs_type, "anon_inode:", NULL,
			&anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
	if (!IS_ERR(root)) {
		struct super_block *s = root->d_sb;
		anon_inode_inode = anon_inode_mkinode(s);
		if (IS_ERR(anon_inode_inode)) {
			dput(root);
			deactivate_locked_super(s);
			root = ERR_CAST(anon_inode_inode);
		}
	}
	return root;
}

/*
 * devpts_mount()
 *
 *     If the '-o newinstance' mount option was specified, mount a new
 *     (private) instance of devpts.  PTYs created in this instance are
 *     independent of the PTYs in other devpts instances.
 *
 *     If the '-o newinstance' option was not specified, mount/remount the
 *     initial kernel mount of devpts.  This type of mount gives the
 *     legacy, single-instance semantics.
 *
 *     The 'newinstance' option is needed to support multiple namespace
 *     semantics in devpts while preserving backward compatibility of the
 *     current 'single-namespace' semantics. i.e all mounts of devpts
 *     without the 'newinstance' mount option should bind to the initial
 *     kernel mount, like mount_single().
 *
 *     Mounts with 'newinstance' option create a new, private namespace.
 *
 *     NOTE:
 *
 *     For single-mount semantics, devpts cannot use mount_single(),
 *     because mount_single()/sget() find and use the super-block from
 *     the most recent mount of devpts. But that recent mount may be a
 *     'newinstance' mount and mount_single() would pick the newinstance
 *     super-block instead of the initial super-block.
 */
static struct dentry *devpts_mount(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data)
{
	int error;
	struct pts_mount_opts opts;
	struct super_block *s;

	error = parse_mount_options(data, PARSE_MOUNT, &opts);
	if (error)
		return ERR_PTR(error);

	/* Require newinstance for all user namespace mounts to ensure
	 * the mount options are not changed.
	 */
	if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
		return ERR_PTR(-EINVAL);

	if (opts.newinstance)
		s = sget(fs_type, NULL, set_anon_super, flags, NULL);
	else
		s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
			 NULL);

	if (IS_ERR(s))
		return ERR_CAST(s);

	if (!s->s_root) {
		error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
		if (error)
			goto out_undo_sget;
		s->s_flags |= MS_ACTIVE;
	}

	memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));

	error = mknod_ptmx(s);
	if (error)
		goto out_undo_sget;

	return dget(s->s_root);

out_undo_sget:
	deactivate_locked_super(s);
	return ERR_PTR(error);
}

/*
 * devpts_get_sb()
 *
 *     If the '-o newinstance' mount option was specified, mount a new
 *     (private) instance of devpts.  PTYs created in this instance are
 *     independent of the PTYs in other devpts instances.
 *
 *     If the '-o newinstance' option was not specified, mount/remount the
 *     initial kernel mount of devpts.  This type of mount gives the
 *     legacy, single-instance semantics.
 *
 *     The 'newinstance' option is needed to support multiple namespace
 *     semantics in devpts while preserving backward compatibility of the
 *     current 'single-namespace' semantics. i.e all mounts of devpts
 *     without the 'newinstance' mount option should bind to the initial
 *     kernel mount, like get_sb_single().
 *
 *     Mounts with 'newinstance' option create a new, private namespace.
 *
 *     NOTE:
 *
 *     For single-mount semantics, devpts cannot use get_sb_single(),
 *     because get_sb_single()/sget() find and use the super-block from
 *     the most recent mount of devpts. But that recent mount may be a
 *     'newinstance' mount and get_sb_single() would pick the newinstance
 *     super-block instead of the initial super-block.
 */
static int devpts_get_sb(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
	int error;
	struct pts_mount_opts opts;
	struct super_block *s;

	error = parse_mount_options(data, PARSE_MOUNT, &opts);
	if (error)
		return error;

	if (opts.newinstance)
		s = sget(fs_type, NULL, set_anon_super, NULL);
	else
		s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);

	if (IS_ERR(s))
		return PTR_ERR(s);

	if (!s->s_root) {
		s->s_flags = flags;
		error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
		if (error)
			goto out_undo_sget;
		s->s_flags |= MS_ACTIVE;
	}

	simple_set_mnt(mnt, s);

	memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));

	error = mknod_ptmx(s);
	if (error)
		goto out_dput;

	return 0;

out_dput:
	dput(s->s_root); /* undo dget() in simple_set_mnt() */

out_undo_sget:
	deactivate_locked_super(s);
	return error;
}

/*
 * Based on mount_nodev() in fs/super.c (need to pass mount options).
 */
struct dentry *esdfs_mount(struct file_system_type *fs_type, int flags,
			    const char *dev_name, void *raw_data)
{
	int error;
	struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);

	if (IS_ERR(s))
		return ERR_CAST(s);

	s->s_flags = flags;

	error = esdfs_read_super(s, dev_name, raw_data,
					flags & MS_SILENT ? 1 : 0);
	if (error) {
		deactivate_locked_super(s);
		return ERR_PTR(error);
	}
	s->s_flags |= MS_ACTIVE;
	return dget(s->s_root);
}

/* A feature which supports mount_nodev() with options */
static struct dentry *mount_nodev_with_options(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *data,
        int (*fill_super)(struct super_block *, const char *, void *, int))

{
	int error;
	struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);

	if (IS_ERR(s))
		return ERR_CAST(s);

	s->s_flags = flags;

	error = fill_super(s, dev_name, data, flags & MS_SILENT ? 1 : 0);
	if (error) {
		deactivate_locked_super(s);
		return ERR_PTR(error);
	}
	s->s_flags |= MS_ACTIVE;
	return dget(s->s_root);
}

static struct dentry *phuang_mount(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *data)
{
    int err;
    struct super_block *sb;

    printk(KERN_DEBUG "%s", __func__);
    sb = sget(fs_type, phuang_test_super, phuang_set_super, data);
    if (IS_ERR(sb))
        return ERR_CAST(sb);

    if (sb->s_root == NULL) {
        sb->s_flags = flags;
        err = phuang_fill_super(sb);
        if (err) {
            deactivate_locked_super(sb);
            return ERR_PTR(err);
        }
        sb->s_flags |= MS_ACTIVE;
    }

    return dget(sb->s_root);
}

static int
cifs_get_sb(struct file_system_type *fs_type,
            int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
    int rc;
    struct super_block *sb = sget(fs_type, NULL, set_anon_super, NULL);

    cFYI(1, "Devname: %s flags: %d ", dev_name, flags);

    if (IS_ERR(sb))
        return PTR_ERR(sb);

    sb->s_flags = flags;

    rc = cifs_read_super(sb, data, dev_name, flags & MS_SILENT ? 1 : 0);
    if (rc) {
        deactivate_locked_super(sb);
        return rc;
    }
    sb->s_flags |= MS_ACTIVE;
    simple_set_mnt(mnt, sb);
    return 0;
}

static struct dentry *
cifs_do_mount(struct file_system_type *fs_type,
              int flags, const char *dev_name, void *data)
{
    int rc;
    struct super_block *sb;

    sb = sget(fs_type, NULL, set_anon_super, NULL);

    cFYI(1, "Devname: %s flags: %d ", dev_name, flags);

    if (IS_ERR(sb))
        return ERR_CAST(sb);

    sb->s_flags = flags;

    rc = cifs_read_super(sb, data, dev_name, flags & MS_SILENT ? 1 : 0);
    if (rc) {
        deactivate_locked_super(sb);
        return ERR_PTR(rc);
    }
    sb->s_flags |= MS_ACTIVE;
    return dget(sb->s_root);
}

static struct dentry *
nilfs_mount(struct file_system_type *fs_type, int flags,
	     const char *dev_name, void *data)
{
	struct nilfs_super_data sd;
	struct super_block *s;
	fmode_t mode = FMODE_READ | FMODE_EXCL;
	struct dentry *root_dentry;
	int err, s_new = false;

	if (!(flags & MS_RDONLY))
		mode |= FMODE_WRITE;

	sd.bdev = blkdev_get_by_path(dev_name, mode, fs_type);
	if (IS_ERR(sd.bdev))
		return ERR_CAST(sd.bdev);

	sd.cno = 0;
	sd.flags = flags;
	if (nilfs_identify((char *)data, &sd)) {
		err = -EINVAL;
		goto failed;
	}

	/*
	 * once the super is inserted into the list by sget, s_umount
	 * will protect the lockfs code from trying to start a snapshot
	 * while we are mounting
	 */
	mutex_lock(&sd.bdev->bd_fsfreeze_mutex);
	if (sd.bdev->bd_fsfreeze_count > 0) {
		mutex_unlock(&sd.bdev->bd_fsfreeze_mutex);
		err = -EBUSY;
		goto failed;
	}
	s = sget(fs_type, nilfs_test_bdev_super, nilfs_set_bdev_super, sd.bdev);
	mutex_unlock(&sd.bdev->bd_fsfreeze_mutex);
	if (IS_ERR(s)) {
		err = PTR_ERR(s);
		goto failed;
	}

	if (!s->s_root) {
		char b[BDEVNAME_SIZE];

		s_new = true;

		/* New superblock instance created */
		s->s_flags = flags;
		s->s_mode = mode;
		strlcpy(s->s_id, bdevname(sd.bdev, b), sizeof(s->s_id));
		sb_set_blocksize(s, block_size(sd.bdev));

		err = nilfs_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
		if (err)
			goto failed_super;

		s->s_flags |= MS_ACTIVE;
	} else if (!sd.cno) {
		int busy = false;

		if (nilfs_tree_was_touched(s->s_root)) {
			busy = nilfs_try_to_shrink_tree(s->s_root);
			if (busy && (flags ^ s->s_flags) & MS_RDONLY) {
				printk(KERN_ERR "NILFS: the device already "
				       "has a %s mount.\n",
				       (s->s_flags & MS_RDONLY) ?
				       "read-only" : "read/write");
				err = -EBUSY;
				goto failed_super;
			}
		}
		if (!busy) {
			/*
			 * Try remount to setup mount states if the current
			 * tree is not mounted and only snapshots use this sb.
			 */
			err = nilfs_remount(s, &flags, data);
			if (err)
				goto failed_super;
		}
	}

	if (sd.cno) {
		err = nilfs_attach_snapshot(s, sd.cno, &root_dentry);
		if (err)
			goto failed_super;
	} else {
		root_dentry = dget(s->s_root);
	}

	if (!s_new)
		blkdev_put(sd.bdev, mode);

	return root_dentry;

 failed_super:
	deactivate_locked_super(s);

 failed:
//.........这里部分代码省略.........