Linux: change return value of if_get_driver to ssize_t.

Differentiate between ioctl error and zero-length driver name in if_get_driver.

diff --git a/src/if-linux.c b/src/if-linux.c
index 3c53a99ab4e78187ca644fead16fe03b6d01de63..9d6f5a92b0586b84a8680505a04d1a5de2cb8338 100644 (file)
--- a/src/if-linux.c
+++ b/src/if-linux.c
@@ -310,8 +310,11 @@ if_init(struct interface *ifp)
        return if_writepathuint(ifp->ctx, path, 1) == -1 ? -1 : 0;
 }
 
-/* Returns number of bytes written to driver, else 0 (error or indeterminate). */
-static size_t
+/* Return values:
+ *   -1 = ioctl error
+ *    0 = no driver name or driver name indeterminate
+ *   >0 = length of driver name written to provided buffer. */
+static ssize_t
 if_get_driver(struct interface *ifp, char *driver, const size_t driverlen)
 {
        struct ethtool_drvinfo drvinfo = { .cmd = ETHTOOL_GDRVINFO };
@@ -320,23 +323,25 @@ if_get_driver(struct interface *ifp, char *driver, const size_t driverlen)
        strlcpy(ifr.ifr_name, ifp->name, sizeof(ifr.ifr_name));
        if (ioctl(ifp->ctx->pf_inet_fd, SIOCETHTOOL, &ifr) != 0) {
                logerr("%s: SIOCETHTOOL ifname=%s", __func__, ifp->name);
-               return 0; /* 0 means error or indeterminate driver name */
+               return -1; /* -1 means ioctl error */
        }
-       return strlcpy(driver, drvinfo.driver, driverlen);
+       return (ssize_t)strlcpy(driver, drvinfo.driver, driverlen);
 }
 
 static bool
 if_cmp_driver(struct interface *ifp, const char *driver)
 {
        char ifdriver[FIELD_SIZEOF(struct ethtool_drvinfo, driver)];
-       size_t n = if_get_driver(ifp, ifdriver, sizeof(ifdriver));
+       ssize_t n = if_get_driver(ifp, ifdriver, sizeof(ifdriver));
 
-       if (n == 0) {
+       if (n == -1) {
                logerr("%s: if_get_driver ifname=%s", __func__, ifp->name);
-               return false;
+       } else if (n == 0) {
+               logerr("%s: driver name empty ifname=%s", __func__, ifp->name);
+       } else if (n > 0) {
+               if (strncmp(ifdriver, driver, n) == 0)
+                       return true;
        }
-       if (strncmp(ifdriver, driver, n) == 0)
-               return true;
        return false;
 }