VFS_MOUNT — mount
    a file system
The
    VFS_MOUNT()
    macro mounts a file system into the system's namespace or updates the
    attributes of an already mounted file system.
The arguments it expects are:
  - mp
- Structure representing the file system.
The
    VFS_MOUNT()
    macro is called both to mount new file systems and to change the attributes
    of an existing file system. If the MNT_UPDATE flag
    is set in mp->mnt_flag then the file system should
    update its internal state from the value of
    mp->mnt_flag. This can be used, for instance, to
    convert a read-only file system to read-write. It is also used by
    mountd(8)
    to update the NFS export information for the file system.
If the MNT_UPDATE flag is not specified,
    then this is a newly mounted file system. The file system code should
    allocate and initialize any private data needed to represent the file system
    (it can use the mp->mnt_data field to store this
    information).
This manual page was written by Doug
    Rabson.