[ovs-dev] [PATCH 2/2] netdev-dpdk: fix snprintf call

Ben Pfaff blp at ovn.org
Thu Jun 14 20:28:05 UTC 2018


On Wed, Jun 13, 2018 at 03:43:04PM -0400, Aaron Conole wrote:
> lib/netdev-dpdk.c: In function :
> lib/netdev-dpdk.c:2865:49: warning:  output may be truncated before the last format character [-Wformat-truncation=]
>         snprintf(vhost_vring, 16, "vring_%d_size", i);
>                                                 ^
> lib/netdev-dpdk.c:2865:9: note:  output between 13 and 17 bytes into a destination of size 16
>         snprintf(vhost_vring, 16, "vring_%d_size", i);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Since vring_num is 16 bits, the largest value ever would only be 17 bytes,
> including the terminating nul.  Stretch it to 18 bytes (as a precaution
> against a signed value, which again would never happen).
> 
> Signed-off-by: Aaron Conole <aconole at redhat.com>
> ---
>  lib/netdev-dpdk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
> index 2e2f568b8..e75943bb2 100644
> --- a/lib/netdev-dpdk.c
> +++ b/lib/netdev-dpdk.c
> @@ -2859,7 +2859,7 @@ netdev_dpdk_vhost_user_get_status(const struct netdev *netdev,
>  
>      for (int i = 0; i < vring_num; i++) {
>          struct rte_vhost_vring vring;
> -        char vhost_vring[16];
> +        char vhost_vring[18];
>  
>          rte_vhost_get_vhost_vring(vid, i, &vring);
>          snprintf(vhost_vring, 16, "vring_%d_size", i);

Thanks for the improvement.

Instead of calculating at all, I think it would be less error-prone to
avoid it, something like this:

diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
index fd496592ba56..040b17f8a34a 100644
--- a/lib/netdev-dpdk.c
+++ b/lib/netdev-dpdk.c
@@ -2883,11 +2883,9 @@ netdev_dpdk_vhost_user_get_status(const struct netdev *netdev,
 
     for (int i = 0; i < vring_num; i++) {
         struct rte_vhost_vring vring;
-        char vhost_vring[18];
-
-        rte_vhost_get_vhost_vring(vid, i, &vring);
-        snprintf(vhost_vring, 16, "vring_%d_size", i);
-        smap_add_format(args, vhost_vring, "%d", vring.size);
+        smap_add_nocopy(args,
+                        xasprintf("vring_%d_size", i),
+                        xasprintf("%d", vring.size));
     }
 
     ovs_mutex_unlock(&dev->mutex);

What do you think?

Thanks,

Ben.


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