[CRIU] Re: [PATCH 3/7] fifo: Add checkpoint restore for fifos v2

[Pavel Emelyanov]

On 06/28/2012 09:20 PM, Cyrill Gorcunov wrote:
> On Thu, Jun 28, 2012 at 09:08:03PM +0400, Pavel Emelyanov wrote:
>>> +static int open_fifo_fd(struct file_desc *d)
>>> +{
>>> +       struct fifo_info *info = container_of(d, struct fifo_info, d);
>>> +       struct reg_file_info *rfi;
>>> +       struct file_desc *rd;
>>> +
>>> +       pr_info("\t\tCreating fifo pipe_id=%#x id=%#x\n",
>>> +               info->fe.pipe_id, info->fe.id);
>>> +
>>> +       rd = find_file_desc_raw(FDINFO_REG, info->fe.id);
>>> +       if (!rd) {
>>> +               pr_perror("Can't find regfile for fifo %#x\n", info->fe.id);
>>> +               return -1;
>>> +       }
>>> +
>>> +       rfi = container_of(rd, struct reg_file_info, d);
>>> +       if (rfi->open != __open_fifo_fd)
>>> +               rfi->open = __open_fifo_fd;
>>> +       rfi->priv = info;
>>> +
>>> +       return open_fe_fd(rd);
>>
>> I don't understand the code above. Why do we find another file_desc while
>> the one we're asked to open is passed to us as an argument?
>>
>>> +}
>>> +
> 
> Because we need to find appropriate reg_file_info descriptor for this
> fifo file descriptor. Look, we dump fifo in two places -- as regfile
> for path and flags sake and as fifo_entry.
> 
> So when we restore the fifo the restorer engine first call open_fifo_fd
> with file_desc which maps fifo_entry then we use reg files engine to
> create fifo file for us
> 
> dump
> 	dump_one_fifo
> 		dump_one_reg_file
> 		write fifo_entry
> 
> restore
> 	open_fifo_fd
> 		manually call for open_fe_fd routine
> 		but open_fe_fd expects reg_file_info,
> 		so we pass 1:1 mapped descriptor.

Ah, now I see, thank!

1. Put the comment about this
2. Use the open_reg_by_id -- it does exactly what you need
3. Pass the real_open callback explicitly as functions argument instead
   of hiding one on file_desc structure