[PATCH v3 2/4] examples/vdpa: fix format overflow warning

[Stephen Hemminger <stephen@networkplumber.org>]

The ifname is limited to 128 characters, but it would allow up
to 128 characters as prefix then could overflow creating ifname.

Change to limit path prefix (iface) to 123 (128 - sizeof("1024"))
to avoid possible format overflow

../examples/vdpa/main.c:501:76: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
  501 |                         snprintf(vports[devcnt].ifname, MAX_PATH_LEN, "%s%d",
      |                                                                            ^
../examples/vdpa/main.c:501:25: note: ‘snprintf’ output between 2 and 139 bytes into a destination of size 128
  501 |                         snprintf(vports[devcnt].ifname, MAX_PATH_LEN, "%s%d",
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  502 |                                         iface, devcnt);
      |

Fixes: 38f8ab0bbc8d ("vhost: make vDPA framework bus agnostic")
Cc: maxime.coquelin@redhat.com
Cc: stable@dpdk.org

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
---
 examples/vdpa/main.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/examples/vdpa/main.c b/examples/vdpa/main.c
index 289db26498..7fd0e55b20 100644
--- a/examples/vdpa/main.c
+++ b/examples/vdpa/main.c
@@ -22,6 +22,8 @@
 
 #define MAX_PATH_LEN 128
 #define MAX_VDPA_SAMPLE_PORTS 1024
+#define stringify(x) (#x)
+#define MAX_VDPA_STR_LEN sizeof(stringify(MAX_VDPA_SAMPLE_PORTS))
 #define RTE_LOGTYPE_VDPA RTE_LOGTYPE_USER1
 
 struct vdpa_port {
@@ -36,7 +38,7 @@ struct vdpa_port {
 
 static struct vdpa_port vports[MAX_VDPA_SAMPLE_PORTS];
 
-static char iface[MAX_PATH_LEN];
+static char iface[MAX_PATH_LEN - MAX_VDPA_STR_LEN];
 static int devcnt;
 static int interactive;
 static int client_mode;
@@ -74,9 +76,8 @@ parse_args(int argc, char **argv)
 			break;
 		/* long options */
 		case 0:
-			if (strncmp(long_option[idx].name, "iface",
-						MAX_PATH_LEN) == 0) {
-				rte_strscpy(iface, optarg, MAX_PATH_LEN);
+			if (!strcmp(long_option[idx].name, "iface")) {
+				rte_strscpy(iface, optarg, sizeof(iface));
 				printf("iface %s\n", iface);
 			}
 			if (!strcmp(long_option[idx].name, "interactive")) {
-- 
2.51.0