linux-kernel - Re: [PATCH] staging: dgap: implement error handling in dgap_tty

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Message-ID: <20140425125952.GE4963@mwanda>
Date:	Fri, 25 Apr 2014 15:59:52 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Mark Hounschell <markh@...pro.net>
Cc:	DaeSeok Youn <daeseok.youn@...il.com>,
	Lidza Louina <lidza.louina@...il.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	devel <devel@...verdev.osuosl.org>,
	driverdev-devel@...uxdriverproject.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: dgap: implement error handling in
 dgap_tty_register()

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@...cle.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@...il.com>
L:      driverdev-devel@...uxdriverproject.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.

regards,
dan carpenter

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