[CRIU] [PATCH v4 11/15] files: Add file_desc_ops::receive method

[Kirill Tkhai]

On 09.06.2016 16:44, Pavel Emelyanov wrote:
> On 06/09/2016 04:31 PM, Kirill Tkhai wrote:
>>
>>
>> On 09.06.2016 16:15, Pavel Emelyanov wrote:
>>> On 06/01/2016 07:03 PM, Kirill Tkhai wrote:
>>>> Currently, nothing is done for master files in receive_fd().
>>>> Add a receive method, which may be useful for subsystems,
>>>> which need it (for queuer-less dgram sockets, going in following
>>>> patches).
>>>>
>>>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>>>> ---
>>>>  criu/files.c         |    3 ++-
>>>>  criu/include/files.h |   10 +++++++++-
>>>>  2 files changed, 11 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/criu/files.c b/criu/files.c
>>>> index bb3b142..22668ec 100644
>>>> --- a/criu/files.c
>>>> +++ b/criu/files.c
>>>> @@ -1053,12 +1053,13 @@ static int open_fd(int pid, struct fdinfo_list_entry *fle)
>>>>  
>>>>  static int receive_fd(int pid, struct fdinfo_list_entry *fle)
>>>>  {
>>>> +	struct file_desc *d = fle->desc;
>>>>  	int tmp;
>>>>  	struct fdinfo_list_entry *flem;
>>>>  
>>>>  	flem = file_master(fle->desc);
>>>>  	if (flem->pid == pid)
>>>> -		return 0;
>>>> +		return d->ops->receive ? d->ops->receive(d, fle->fe->fd) : 0;
>>>
>>> Erm... This path is not receiving an fd, it's just us who's the
>>> file master.
>>
>> I don't understand your comment. Could you please explain what you mean?
> 
> The "return 0" you've removed doesn't mean "receive descriptor". It means "OK,
> the descriptor is already at the place we want it to". And renaming this
> into "go ahead and to fd-specific receiving" is confusing.
> 
> Describe what operation you plan to "virtualize" with this callback.

It's quite difficult to choose true name for this. It's not a specific operation,
it's just about a time between open and post_open. We may add new state
in fd_open_state::states instead..

>>>>  
>>>>  	pr_info("\tReceive fd for %d\n", fle->fe->fd);
>>>>  
>>>> diff --git a/criu/include/files.h b/criu/include/files.h
>>>> index 5e3d6dc..f0d5f23 100644
>>>> --- a/criu/include/files.h
>>>> +++ b/criu/include/files.h
>>>> @@ -90,7 +90,15 @@ struct file_desc_ops {
>>>>  	int			(*open)(struct file_desc *d);
>>>>  	/*
>>>>  	 * Called on a file when all files of that type are opened
>>>> -	 * and with the fd being the "restored" one.
>>>> +	 * and with the fd being the "restored" one. This may be used
>>>> +	 * to receive some additional file descriptors that are needed
>>>> +	 * at post_open stage.
>>>> +	 */
>>>> +	int			(*receive)(struct file_desc *d, int fd);
>>>> +	/*
>>>> +	 * Called on a file when all files of that type are opened
>>>> +	 * and with the fd being the "restored" one and all data need
>>>> +	 * to complete restore is received.
>>>>  	 */
>>>>  	int			(*post_open)(struct file_desc *d, int fd);
>>>>  	/*
>>>>
>>>> _______________________________________________
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>>>> .
>>>>
>>>
>> .
>>
>