对于前面的根目录文件系统的安装中涉及到了mount系统调用的调用,这里我们考虑一个文件系统将被安装在一个已经安装文件系统之上的情形,即调用mount系统调用实现。mount系统调用被用来安装一个普通文件系统,他的服务例程为sys_mount()。
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SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
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char __user *, type, unsigned long, flags, void __user *, data)
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{
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int ret;
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char *kernel_type;
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char *kernel_dir;
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char *kernel_dev;
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unsigned long data_page;
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ret = copy_mount_string(type, &kernel_type);
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if (ret < 0)
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goto out_type;
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kernel_dir = getname(dir_name);
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if (IS_ERR(kernel_dir)) {
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ret = PTR_ERR(kernel_dir);
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goto out_dir;
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}
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ret = copy_mount_string(dev_name, &kernel_dev);
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if (ret < 0)
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goto out_dev;
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ret = copy_mount_options(data, &data_page);
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if (ret < 0)
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goto out_data;
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ret = do_mount(kernel_dev, kernel_dir, kernel_type, flags,
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(void *) data_page);
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free_page(data_page);
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out_data:
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kfree(kernel_dev);
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out_dev:
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putname(kernel_dir);
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out_dir:
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kfree(kernel_type);
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out_type:
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return ret;
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}
下面是主体实现
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long do_mount(char *dev_name, char *dir_name, char *type_page,
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unsigned long flags, void *data_page)
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{
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struct path path;
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int retval = 0;
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int mnt_flags = 0;
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if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
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flags &= ~MS_MGC_MSK;
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if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
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return -EINVAL;
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if (data_page)
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((char *)data_page)[PAGE_SIZE - 1] = 0;
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if (!(flags & MS_NOATIME))
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mnt_flags |= MNT_RELATIME;
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if (flags & MS_NOSUID)
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mnt_flags |= MNT_NOSUID;
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if (flags & MS_NODEV)
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mnt_flags |= MNT_NODEV;
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if (flags & MS_NOEXEC)
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mnt_flags |= MNT_NOEXEC;
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if (flags & MS_NOATIME)
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mnt_flags |= MNT_NOATIME;
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if (flags & MS_NODIRATIME)
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mnt_flags |= MNT_NODIRATIME;
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if (flags & MS_STRICTATIME)
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mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
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if (flags & MS_RDONLY)
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mnt_flags |= MNT_READONLY;
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flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
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MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
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MS_STRICTATIME);
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retval = kern_path(dir_name, LOOKUP_FOLLOW, &path);
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if (retval)
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return retval;
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retval = security_sb_mount(dev_name, &path,
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type_page, flags, data_page);
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if (retval)
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goto dput_out;
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if (flags & MS_REMOUNT)
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retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
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data_page);
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else if (flags & MS_BIND)
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retval = do_loopback(&path, dev_name, flags & MS_REC);
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else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
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retval = do_change_type(&path, flags);
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else if (flags & MS_MOVE)
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retval = do_move_mount(&path, dev_name);
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else
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retval = do_new_mount(&path, type_page, flags, mnt_flags,
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dev_name, data_page);
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dput_out:
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path_put(&path);
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return retval;
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}
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static int do_new_mount(struct path *path, char *type, int flags,
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int mnt_flags, char *name, void *data)
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{
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struct vfsmount *mnt;
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if (!type)
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return -EINVAL;
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if (!capable(CAP_SYS_ADMIN))
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return -EPERM;
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lock_kernel();
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*/
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mnt = do_kern_mount(type, flags, name, data);
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unlock_kernel();
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if (IS_ERR(mnt))
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return PTR_ERR(mnt);
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return do_add_mount(mnt, path, mnt_flags, NULL);
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}
do_kern_mount函数在前面初始化中介绍过了,下面看do_add_mount函数用于将文件系统整合到系统中。
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int do_add_mount(struct vfsmount *newmnt, struct path *path,
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int mnt_flags, struct list_head *fslist)
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{
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int err;
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down_write(&namespace_sem);
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while (d_mountpoint(path->dentry) &&
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follow_down(path))
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;
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err = -EINVAL;
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if (!(mnt_flags & MNT_SHRINKABLE) && !check_mnt(path->mnt))
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goto unlock;
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err = -EBUSY;
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if (path->mnt->mnt_sb == newmnt->mnt_sb &&
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path->mnt->mnt_root == path->dentry)
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goto unlock;
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err = -EINVAL;
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if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
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goto unlock;
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newmnt->mnt_flags = mnt_flags;
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if ((err = graft_tree(newmnt, path)))
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goto unlock;
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if (fslist)
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list_add_tail(&newmnt->mnt_expire, fslist);
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up_write(&namespace_sem);
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return 0;
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unlock:
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up_write(&namespace_sem);
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mntput(newmnt);
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return err;
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}
新安装的文件系统对象链入系统树。
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static int graft_tree(struct vfsmount *mnt, struct path *path)
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{
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int err;
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if (mnt->mnt_sb->s_flags & MS_NOUSER)
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return -EINVAL;
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if (S_ISDIR(path->dentry->d_inode->i_mode) !=
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S_ISDIR(mnt->mnt_root->d_inode->i_mode))
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return -ENOTDIR;
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err = -ENOENT;
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mutex_lock(&path->dentry->d_inode->i_mutex);
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if (IS_DEADDIR(path->dentry->d_inode))
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goto out_unlock;
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err = security_sb_check_sb(mnt, path);
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if (err)
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goto out_unlock;
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err = -ENOENT;
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if (!d_unlinked(path->dentry))
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err = attach_recursive_mnt(mnt, path, NULL);
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out_unlock:
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mutex_unlock(&path->dentry->d_inode->i_mutex);
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if (!err)
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security_sb_post_addmount(mnt, path);
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return err;
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}
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static int attach_recursive_mnt(struct vfsmount *source_mnt,
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struct path *path, struct path *parent_path)
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{
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LIST_HEAD(tree_list);
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struct vfsmount *dest_mnt = path->mnt;
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struct dentry *dest_dentry = path->dentry;
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struct vfsmount *child, *p;
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int err;
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if (IS_MNT_SHARED(dest_mnt)) {
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err = invent_group_ids(source_mnt, true);
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if (err)
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goto out;
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}
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err = propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list);
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if (err)
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goto out_cleanup_ids;
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if (IS_MNT_SHARED(dest_mnt)) {
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for (p = source_mnt; p; p = next_mnt(p, source_mnt))
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set_mnt_shared(p);
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}
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spin_lock(&vfsmount_lock);
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if (parent_path) {
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detach_mnt(source_mnt, parent_path);
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attach_mnt(source_mnt, path);
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touch_mnt_namespace(parent_path->mnt->mnt_ns);
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} else {
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mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
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commit_tree(source_mnt);
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}
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list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
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list_del_init(&child->mnt_hash);
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commit_tree(child);
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}
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spin_unlock(&vfsmount_lock);
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return 0;
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out_cleanup_ids:
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if (IS_MNT_SHARED(dest_mnt))
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cleanup_group_ids(source_mnt, NULL);
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out:
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return err;
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}
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