Re: [PATCH v2] USB: serial: io_edgeport: mark expected switch fall-throughs

[Greg Kroah-Hartman]

On Thu, May 02, 2019 at 09:28:37AM -0500, Gustavo A. R. Silva wrote:
> 
> 
> On 5/2/19 8:56 AM, Johan Hovold wrote:
> > On Thu, May 02, 2019 at 08:22:30AM -0500, Gustavo A. R. Silva wrote:
> >>
> >>
> >> On 5/2/19 5:26 AM, Johan Hovold wrote:
> >>> On Wed, May 01, 2019 at 04:33:29PM -0500, Gustavo A. R. Silva wrote:
> >>>> In preparation to enabling -Wimplicit-fallthrough, mark switch
> >>>> cases where we are expecting to fall through.
> >>>>
> >>>> This patch fixes the following warnings:
> >>>>
> >>>> drivers/usb/serial/io_edgeport.c: In function âprocess_rcvd_dataâ:
> >>>> drivers/usb/serial/io_edgeport.c:1750:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
> >>>>     if (bufferLength == 0) {
> >>>>        ^
> >>>> drivers/usb/serial/io_edgeport.c:1755:3: note: here
> >>>>    case EXPECT_HDR2:
> >>>>    ^~~~
> >>>> drivers/usb/serial/io_edgeport.c:1810:8: warning: this statement may fall through [-Wimplicit-fallthrough=]
> >>>>      if (bufferLength == 0) {
> >>>>         ^
> >>>> drivers/usb/serial/io_edgeport.c:1816:3: note: here
> >>>>    case EXPECT_DATA: /* Expect data */
> >>>>    ^~~~
> >>>>
> >>>> Warning level 3 was used: -Wimplicit-fallthrough=3
> >>>>
> >>>> Notice that, in this particular case, the code comments are modified
> >>>> in accordance with what GCC is expecting to find.
> >>>>
> >>>> This patch is part of the ongoing efforts to enable
> >>>> -Wimplicit-fallthrough.
> >>>>
> >>>> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> >>>> ---
> >>>> Changes in v2:
> >>>>  - Warning level 3 is now used: -Wimplicit-fallthrough=3
> >>>>    instead of warning level 2.
> >>>>  - All warnings in the switch statement are addressed now.
> >>>>
> >>>> Notice that these are the last remaining fall-through warnings
> >>>> in the USB subsystem. :)
> >>>
> >>>>  drivers/usb/serial/io_edgeport.c | 3 ++-
> >>>>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
> >>>> index 4ca31c0e4174..7ad10328f4e2 100644
> >>>> --- a/drivers/usb/serial/io_edgeport.c
> >>>> +++ b/drivers/usb/serial/io_edgeport.c
> >>>> @@ -1751,7 +1751,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
> >>>>  				edge_serial->rxState = EXPECT_HDR2;
> >>>>  				break;
> >>>>  			}
> >>>> -			/* otherwise, drop on through */
> >>>> +			/* Fall through - otherwise, drop on through */
> >>>>  		case EXPECT_HDR2:
> >>>>  			edge_serial->rxHeader2 = *buffer;
> >>>>  			++buffer;
> >>>> @@ -1813,6 +1813,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
> >>>>  				}
> >>>>  				/* Else, drop through */
> >>>>  			}
> >>>> +			/* Fall through */
> >>>>  		case EXPECT_DATA: /* Expect data */
> >>>
> >>> Looks like you forgot to take the original review feedback you got into
> >>> account:
> >>>
> >>> 	https://lkml.kernel.org/r/87k1zf4k24.fsf@xxxxxxxxxxxxxxxxx
> >>>
> >>
> >> Oh, the thing is that the fall-through comments have to be placed at
> >> the very bottom of the case. Also, based on that feedback, this time
> >> I left the "Else, drop through" comment in place, so people can be
> >> informed that such fall-through is conditional.
> >>
> >> What do you think about this:
> >>
> >> diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
> >> index 4ca31c0e4174..52f27fc82563 100644
> >> --- a/drivers/usb/serial/io_edgeport.c
> >> +++ b/drivers/usb/serial/io_edgeport.c
> >> @@ -1751,7 +1751,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
> >>                                 edge_serial->rxState = EXPECT_HDR2;
> >>                                 break;
> >>                         }
> >> -                       /* otherwise, drop on through */
> >> +                       /* Fall through - otherwise, drop on through */
> >>                 case EXPECT_HDR2:
> >>                         edge_serial->rxHeader2 = *buffer;
> >>                         ++buffer;
> >> @@ -1813,6 +1813,11 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
> >>                                 }
> >>                                 /* Else, drop through */
> >>                         }
> >> +                       /* Beware that, currently, there are at least three
> >> +                        * break statements in this case block, so the
> >> +                        * fall-through marked below is NOT unconditional.
> >> +                        */
> >> +                       /* Fall through */
> >>                 case EXPECT_DATA: /* Expect data */
> >>                         if (bufferLength < edge_serial->rxBytesRemaining) {
> >>                                 rxLen = bufferLength;
> > 
> > It's better than v2, but I thought you said you were gonna look into
> > restructuring the code to maintain (or even improve) readability?
> > 
> 
> At first, I thought about that, but now I don't think that's realistic.
> I'd turn the if-else into a switch, and based on the history of feedback
> on this patch, we will end up having the same complains about the break
> statements in that new switch and the possibility of a fall-through to
> case EXPECT_DATA. At the end I would still have to add a comment explaining
> that the last fall-through mark in unconditional.

I love it how no one is blaming the original author of this code (i.e.
me...)

Let me see if I can fix it up to be more "sane", this is my fault.

thanks,

greg k-h