Re: [PATCH] staging: dgap: implement error handling in dgap_tty_register()

[DaeSeok Youn]

Hi,

please check below my comments.

2014-04-25 23:41 GMT+09:00 Mark Hounschell <markh@xxxxxxxxxx>:
> On 04/25/2014 08:59 AM, Dan Carpenter wrote:
>> On Fri, Apr 25, 2014 at 08:29:41AM -0400, Mark Hounschell wrote:
>>> On 04/25/2014 07:02 AM, DaeSeok Youn wrote:
>>>> Hi, Dan.
>>>>
>>>> 2014-04-25 18:26 GMT+09:00 Dan Carpenter <dan.carpenter@xxxxxxxxxx>:
>>>>> Mark, maybe you should add yourself to the MAINTAINERS entry for this
>>>>> driver?
>>>>>
>>>
>>> I'll look into this. I am clueless on what that would actually mean.
>>>
>>
>> Just add your name with Lidza in the MAINTAINERS file so that people
>> will CC you on all the patches.
>>
>> DIGI EPCA PCI PRODUCTS
>> M:      Lidza Louina <lidza.louina@xxxxxxxxx>
>> L:      driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx
>> S:      Maintained
>> F:      drivers/staging/dgap/
>>
>> You don't have to do it if you don't want to, but you seem to be working
>> on this driver and I'm going to refer questions to you either way.  :P
>>
>>>>> On Fri, Apr 25, 2014 at 04:04:59PM +0900, Daeseok Youn wrote:
>>>>>> @@ -1263,7 +1277,8 @@ static int dgap_tty_register(struct board_t *brd)
>>>>>>               /* Register tty devices */
>>>>>>               rc = tty_register_driver(brd->SerialDriver);
>>>>>>               if (rc < 0)
>>>>>> -                     return rc;
>>>>>> +                     goto free_print_ttys;
>>>>>> +
>>>>>>               brd->dgap_Major_Serial_Registered = TRUE;
>>>>>>               dgap_BoardsByMajor[brd->SerialDriver->major] = brd;
>>>>>>               brd->dgap_Serial_Major = brd->SerialDriver->major;
>>>>>> @@ -1273,13 +1288,29 @@ static int dgap_tty_register(struct board_t *brd)
>>>>>>               /* Register Transparent Print devices */
>>>>>>               rc = tty_register_driver(brd->PrintDriver);
>>>>>>               if (rc < 0)
>>>>>> -                     return rc;
>>>>>> +                     goto unregister_serial_drv;
>>>>>> +
>>>>>>               brd->dgap_Major_TransparentPrint_Registered = TRUE;
>>>>>>               dgap_BoardsByMajor[brd->PrintDriver->major] = brd;
>>>>>>               brd->dgap_TransparentPrint_Major = brd->PrintDriver->major;
>>>>>>       }
>>>>>>
>>>>>>       return rc;
>>>>>> +
>>>>>> +unregister_serial_drv:
>>>>>> +     tty_unregister_driver(brd->SerialDriver);
>>>>>
>>>>> We only register the ->SerialDriver if someone else hasn't registered it
>>>>> first?  So this should be:
>>>>>
>>>>>         if (we_were_the_ones_who_registered_the_serial_driver)
>>>>>                 tty_unregister_driver(brd->SerialDriver);
>>>>>
>>>>> I haven't followed looked at this.  Who else is registering the serial
>>>>> driver?  You have looked at this, what do you think?  Or Mark.
>>>>
>>>
>>> registering the brd->XxxxxDriver is only done when a board is detected
>>> and only during the firmware_load process. If we fail to
>>> tty_register_driver do we _need_ to tty_unregister_driver? Isn't that
>>> like freeing after an alloc failure?
>>
>> The allocation is conditional so the free should be conditional.  If we
>> didn't allocate it, then we shouldn't free it.
>>
>> It wouldn't have even been a question except I'm not sure the allocation
>> is *really* conditional because brd->dgap_Major_Serial_Registered might
>> always be "false" like you guys seem to be saying.
>>
>>>
>>>> I think brd struct is from dgap_Board array as global static variable
>>>> when this function is
>>>> called. So brd->dgap_Major_Serial_Registered is always "false".
>>>> If dgap_NumBoards is less than MAXBOARDS, brd->SerialDriver should be
>>>> registered.
>>>>
>>>> I'm not sure..
>>>>
>>>
>>> I don't see any check for (dgap_NumBoards <  MAXBOARDS), which I think I
>>> probably should, but I do see we are calling dgap_tty_register, which
>>> can fail, without actually checking the return value. Also, yes,
>>> dgap_Major_Xxxx_Registered seems to be always "false" until registered,
>>> and it looks like dgap_Major_Xxxxx_Registered flags could be removed
>>> because the only places we can unregister is at module_cleanup or
>>> "after" it is already registered.
>>>
>>> What is the driver _supposed_ to do if we fail something on the second
>>> or later board? Is the driver supposed to cleanup and exit or are we
>>> supposed to stay loaded for the board/boards that are usable?
>>
>> Stay loaded.
>>
>
> Then these tests on brd->dgap_Major_Serial_Registered need to stay in
> there. If I have 3 boards and the second fails in some way, if I rmmod
> the driver they will protect from unregistering a never registered one.
> At least in the unregister code path. There is probably no need for them
> in the register code path. I'll work up a patch for this.

Should I update my patch?

I think "if (!brd->dgap_Major_XXX_Registered)" line can be removed in this
function, because if tty_register_driver() is failed just set "false"
to "dgap_Major_XXX_Registered".
dgap_Major_XXX_Registered only is used in cleaup function, right?
So code like below
               rc = tty_register_driver(brd->PrintDriver);
               if (rc < 0)
                     goto unregister_serial_drv;
               brd->dgap_Major_TransparentPrint_Registered = TRUE;
...
unregister_serial_drv;
               brd->dgap_Major_Serial_Registered = false;
                tty_unregister_driver(brd->SerialDriver);

Thanks.

Regards,
Daeseok Youn.

>
> I need to look at the (dgap_NumBoards <  MAXBOARDS) thing too.
>
> Mark
>
>
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