[libvirt] [PATCH 3/4] qemu: add missing break in qemuDomainDeviceCalculatePCIConnectFlags

[Laine Stump]

On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
> One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags
> was missing a break that could result it in falling through to
> an incorrect codepath.

Actually that's not true. Every codepath of the preceding case ends with 
a "return blah".  This is true for the entire function - every case of 
every switch in the function ends with "return blah". The entire purpose 
of the function is to determine the flags value, and there are no 
resources that need cleaning up before returning, so as soon as the 
value is determined, it immediately returns.

I suppose it could be rewritten to change all of those into "ret = blah; 
break;", then "return ret;" at the end, but it seemed safer to return 
immediately than to trust that no new code would be added later in the 
function (and also it's more compact)

I wonder if this is just a more extreme case of the logic in whatever 
check necessitated that I add an extra "return 0" at the very end of the 
function. (that happens even in gcc 6.x; at an earlier point when the 
function was simpler, that wasn't needed, but after some additions it 
started producing the "control reaches end of function that requires a 
return value" or whatever that warning is, and the only way to eliminate 
it was with the extra return 0.)

If adding the break shuts up the warning, then I guess ACK, but it would 
probably be better if 1) gcc fixed their incorrect warning, or 2) we 
switched the entire function to use the less-compact "ret = blah; 
break;" style instead of returning directly, so there wasn't a single 
stray break sitting in the middle.


>
> Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
> ---
>   src/qemu/qemu_domain_address.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/src/qemu/qemu_domain_address.c b/src/qemu/qemu_domain_address.c
> index 5b75044..27ca010 100644
> --- a/src/qemu/qemu_domain_address.c
> +++ b/src/qemu/qemu_domain_address.c
> @@ -553,6 +553,7 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev,
>               return pciFlags;
>           }
>       }
> +        break;
>   
>       case VIR_DOMAIN_DEVICE_FS:
>           /* the only type of filesystem so far is virtio-9p-pci */