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

Mark Hounschell
2014-04-25T14:41:10Z

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@oracle.com>:
>>>> 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@gmail.com>
> L: driverdev-devel@linuxdriverproject.org
> 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