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From: Laszlo Ersek <lersek@redhat.com>
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Date: Fri, 19 Feb 2016 21:59:19 +0100
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Subject: Re: [Qemu-devel] [PATCH 1/1] virtio-rng: fix condition checking on
 period_ms
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To: Wei Huang <wei@redhat.com>, qemu-devel@nongnu.org
Cc: qemu-trivial@nongnu.org, mst@redhat.com

On 02/19/16 21:57, Laszlo Ersek wrote:
> On 02/19/16 19:13, Wei Huang wrote:
>> The condition checking on vrng->conf.period_ms appears to be wrong,
>> conflicting with the error comment following it.
>>
>> Signed-off-by: Wei Huang <wei@redhat.com>
>> ---
>>  hw/virtio/virtio-rng.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
>> index 473c044..a06427c 100644
>> --- a/hw/virtio/virtio-rng.c
>> +++ b/hw/virtio/virtio-rng.c
>> @@ -149,7 +149,7 @@ static void virtio_rng_device_realize(DeviceState *dev, Error **errp)
>>      VirtIORNG *vrng = VIRTIO_RNG(dev);
>>      Error *local_err = NULL;
>>  
>> -    if (!vrng->conf.period_ms > 0) {
>> +    if (!(vrng->conf.period_ms > 0)) {
>>          error_setg(errp, "'period' parameter expects a positive integer");
>>          return;
>>      }
>>
> 
> The current condition is absolutely weird, but I think it happens to
> work correctly:
> 
> Period_ms has type uint32_t. If it is positive, then !period_ms is zero.
> 0>0 is false, hence the error message is not printed.
> 
> If period_ms is zero, then !period_ms is 1. 1>0 is true, hence the error
> message is printed.
> 
> I would rewrite the check as
> 
>     if (vrng->conf.period_ms == 0) {
>         error_setg(...)

... actually, what the heck are you looking at? :) This has been fixed
up in:

commit a3a292c420d2fec3c07a7ca56fbb064cd57a298a
Author: Amit Shah <amit.shah@redhat.com>
Date:   Thu Dec 11 13:17:42 2014 +0530

    virtio-rng: fix check for period_ms validity

Thanks
Laszlo