PivotRoot调用失败，Invalid arguments error

[taikulawo]

问题

问题的存档放在如下的 commit

https://github.com/iamwwc/wwcdocker/tree/5490793ea136bdffabb297b169197ea41fd6b4ec

根据 mount namespace 的文档

http://man7.org/linux/man-pages/man7/mount_namespaces.7.html#top_of_page

 Notwithstanding the fact that the default propagation type for new
       mount points is in many cases MS_PRIVATE, MS_SHARED is typically more
       useful.  For this reason, systemd(1) automatically remounts all mount
       points as MS_SHARED on system startup.  Thus, on most modern systems,
       the default propagation type is in practice MS_SHARED.

systemd会将 fs 修改为 shared，但从 pivot_root文档中Errors session可知：

http://man7.org/linux/man-pages/man2/pivot_root.2.html

  EINVAL new_root is not a mount point.

       EINVAL put_old is not underneath new_root.

       EINVAL The current root is on the rootfs (initial ramfs) filesystem.

       EINVAL Either the mount point at new_root, or the parent mount of
              that mount point, has propagation type MS_SHARED.

       EINVAL put_old is a mount point and has the propagation type
              MS_SHARED.

pivot root 不允许 parent mount point 和 new mount point 是 shared。

那我们应该如何修复这个问题？

1. 可以修改为 MS_PRIVATE(mount --make-rprivate /)
2. 根据 docker runC 注释

https://github.com/opencontainers/runc/blob/a6606a7ae9d9e00bf0a8721ee1d4eb095fcc4ad6/libcontainer/rootfs_linux.go#L655

https://github.com/opencontainers/runc/blob/a6606a7ae9d9e00bf0a8721ee1d4eb095fcc4ad6/libcontainer/rootfs_linux.go#L739

也可以使用 MS_SLAVE