[dpdk-dev] [PATCH v2] vhost: fix false-positive warning from clang 5

[Bruce Richardson <bruce.richardson@intel.com>]

When compiling with clang extra warning flags, such as used by default with
meson, a warning is given in iotlb.c:

../lib/librte_vhost/iotlb.c:318:6: warning: variable 'socket' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]

This is a false positive, as the socket value will be initialized by the
call to get_mempolicy in the case where the NUMA build-time flag is set,
and in cases where it is not set, "if (ret)" will always be true as ret is
initialized to -1 and never changed.

However, this is not immediately obvious, and is perhaps a little fragile,
as it will break if other code using ret is subsequently added above the
call to get_mempolicy by someone unaware of this subtle dependency.
Therefore, we can fix the warning and making the code more robust by
explicitly initializing socket to zero, and moving the extra condition
check on the return from get_mempolicy() into the #ifdef

Fixes: d012d1f293f4 ("vhost: add IOTLB helper functions")

CC: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>

---
V2: remove ret variable completely, to avoid unused var warnings when
compiling with the build-time numa option disabled.
---
 lib/librte_vhost/iotlb.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/lib/librte_vhost/iotlb.c b/lib/librte_vhost/iotlb.c
index 066c37a73..05c278040 100644
--- a/lib/librte_vhost/iotlb.c
+++ b/lib/librte_vhost/iotlb.c
@@ -300,7 +300,7 @@ vhost_user_iotlb_init(struct virtio_net *dev, int vq_index)
 {
 	char pool_name[RTE_MEMPOOL_NAMESIZE];
 	struct vhost_virtqueue *vq = dev->virtqueue[vq_index];
-	int ret = -1, socket;
+	int socket = 0;
 
 	if (vq->iotlb_pool) {
 		/*
@@ -313,10 +313,9 @@ vhost_user_iotlb_init(struct virtio_net *dev, int vq_index)
 	}
 
 #ifdef RTE_LIBRTE_VHOST_NUMA
-	ret = get_mempolicy(&socket, NULL, 0, vq, MPOL_F_NODE | MPOL_F_ADDR);
-#endif
-	if (ret)
+	if (get_mempolicy(&socket, NULL, 0, vq, MPOL_F_NODE | MPOL_F_ADDR) != 0)
 		socket = 0;
+#endif
 
 	rte_rwlock_init(&vq->iotlb_lock);
 	rte_rwlock_init(&vq->iotlb_pending_lock);
-- 
2.13.6