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

[Mark Hounschell]

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.

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

Mark


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