mark: fs syscall call path

mount(2)

SYSCALL_DEFINE.(mount, ...)
  do_mount()
    do_new_mount()
      type = get_fs_type(char * fstype)
        vfs_kern_mount(type, ...)
          mount_fs(type, ...)
            type->mount(type, ...)

open(2)

SYSCALL_DEFINE.(open, ...)
  do_sys_open()
    fd = get_unused_fd_flags()
    file = do_filp_open()
      path_openat()
        file = get_empty_filp()
        link_path_walk()
          xxx_lookup() --> {inode = xxx_iget(_sb, )} --> {init i_op & i_fop}
        do_last()
          lookup_open() --> may_open() --> {if (path->mnt->mnt_flags & MNT_NODEV) return -EACCES}
        V

//xxx_lookup->new_inode|xxx_iget()->new_inode_pseudo()->alloc_inode()
//'.->i_fop =' {inode->i_fop = de->proc_fops;},{inode->i_fop = &xxx_file_ops;}
//finish_open()->do_dentry_open()->{f->f_op = fops_get(inode->i_fop);}
//open = f->f_op->open; error = open(inode, f); //some filesystem there is open() defined them self

generic_file_open
ext4_file_open
xfs_file_open
nfs_file_open

//对于特殊文件(chr,blk,fifo,sock) 每个文件系统初始化inode时，都会调用init_special_inode

const struct file_operations def_chr_fops = {  
    .open = chrdev_open,  
};
def_blk_fops
def_fifo_fops
bad_sock_fops
fs/xxx/inode.c: xxx_iget() --> init_special_inode()

fs/nfs/inode.c: nfs_fhget() --> init_special_inode()
对special文件，nfs处理有问题 //nfs 里面也是同样处理:注册的是本机特殊设备的fops;
如果用户不知道，导出/dev远程访问的话，其实访问的还是本机的设备文件；
    nfs应该注册自定义的fops,

read(2)

SYSCALL_DEFINE.(read, ...)
  vfs_read()
    file->f_op->read()
      //ext4 ...
      ext4_file_operations.read = do_sync_read  //struct file_operations
        ext4_file_operations.aio_read = generic_file_aio_read
          do_generic_file_read()
            mapping->a_ops->readpage()
              ext4_ordered_aops.readpage = ext4_readpage  //struct address_space_operations
                ext4_get_block()

      //proc default ...
      //entry = create_proc_entry( fops=NULL ); entry->read_proc = xxxx_read_proc
      proc_file_operations.read = proc_file_read
        __proc_file_read()
           dp->read_proc()  //if NULL -EIO
      //proc special 1 ...
      //proc_create( fops=arp_seq_fops )
      arp_seq_fops.read
        seq_read()

      //proc special 2 ... http://blog.chinaunix.net/uid-20564848-id-73759.html
      proc_sys_file_operations.read = proc_sys_read
        table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
          table->proc_handler()  //.proc_handler = xxxx()

      //proc special 3 ...
      cache_file_operations_procfs.read
        cache_read_procfs()
          cache_read()
            /*find next request*/
            copy_to_user()