Re: [Xen-devel] [PATCH] PCI: Mark expected switch fall-throughs

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.03.19 at 19:27, <gustavo@xxxxxxxxxxxxxx> wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch
> cases where we are expecting to fall through.
> 
> This patch fixes the following warnings:
> 
> drivers/pci/proc.c: In function ‘proc_bus_pci_ioctl’:
> drivers/pci/proc.c:216:6: warning: this statement may fall through 
> [-Wimplicit-fallthrough=]
>    if (arch_can_pci_mmap_wc()) {
>       ^
> drivers/pci/proc.c:225:2: note: here
>   default:
>   ^~~~~~~
> 
> drivers/pci/xen-pcifront.c: In function ‘pcifront_backend_changed’:
> drivers/pci/xen-pcifront.c:1105:6: warning: this statement may fall through 
> [-Wimplicit-fallthrough=]
>    if (xdev->state == XenbusStateClosed)
>       ^
> drivers/pci/xen-pcifront.c:1108:2: note: here
>   case XenbusStateClosing:
>   ^~~~
> 
> Notice that, in this particular case, the /* fall through */
> comment is placed at the very bottom of the case statement,
> which is what GCC is expecting to find.
> 
> Warning level 3 was used: -Wimplicit-fallthrough=3
> 
> This patch is part of the ongoing efforts to enable
> -Wimplicit-fallthrough.

None of the above explains why ...

> --- a/drivers/pci/xen-pcifront.c
> +++ b/drivers/pci/xen-pcifront.c
> @@ -1104,7 +1104,7 @@ static void __ref pcifront_backend_changed(struct 
> xenbus_device *xdev,
>       case XenbusStateClosed:
>               if (xdev->state == XenbusStateClosed)
>                       break;
> -             /* Missed the backend's CLOSING state -- fallthrough */
> +             /* fall through - Missed the backend's CLOSING state. */

... the original comment here wasn't good enough.

Jan


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