VFS之mnt命名空间

 内核针对文件系统设置的命名空间：

struct mnt_namespace { atomic_t  count; struct ns_common ns; struct mount * root; struct list_head list; struct user_namespace *user_ns; struct ucounts  *ucounts; u64   seq; /* Sequence number to prevent loops */ wait_queue_head_t poll; u64 event; unsigned int  mounts; /* # of mounts in the namespace */ unsigned int  pending_mounts;};