get rid of remaining -Wunused-result warnings

Although not fundamentally necessary to check return codes in these
spots, preventing the warnings will put new ones into focus.
Signed-off-by: Phil Sutter <phil@nwl.cc>

misc/ifstat.c

@@ -819,7 +819,8 @@ int main(int argc, char *argv[])
 			}
 			if (uptime >= 0 && time(NULL) >= stb.st_mtime+uptime) {
 				fprintf(stderr, "ifstat: history is aged out, resetting\n");
-				ftruncate(fileno(hist_fp), 0);
+				if (ftruncate(fileno(hist_fp), 0))
+					perror("ifstat: ftruncate");
 			}
 		}
 
@@ -862,7 +863,8 @@ int main(int argc, char *argv[])
 	}
 
 	if (!no_update) {
-		ftruncate(fileno(hist_fp), 0);
+		if (ftruncate(fileno(hist_fp), 0))
+			perror("ifstat: ftruncate");
 		rewind(hist_fp);
 
 		json_output = 0;

misc/lnstat_util.c

@@ -138,7 +138,8 @@ static int lnstat_scan_fields(struct lnstat_file *lf)
 	char buf[FGETS_BUF_SIZE];
 
 	rewind(lf->fp);
-	fgets(buf, sizeof(buf)-1, lf->fp);
+	if (!fgets(buf, sizeof(buf)-1, lf->fp))
+		return -1;
 
 	return __lnstat_scan_fields(lf, buf);
 }

misc/nstat.c

@@ -649,7 +649,8 @@ int main(int argc, char *argv[])
 			}
 			if (uptime >= 0 && time(NULL) >= stb.st_mtime+uptime) {
 				fprintf(stderr, "nstat: history is aged out, resetting\n");
-				ftruncate(fileno(hist_fp), 0);
+				if (ftruncate(fileno(hist_fp), 0) < 0)
+					perror("nstat: ftruncate");
 			}
 		}
 
@@ -693,7 +694,8 @@ int main(int argc, char *argv[])
 			dump_incr_db(stdout);
 	}
 	if (!no_update) {
-		ftruncate(fileno(hist_fp), 0);
+		if (ftruncate(fileno(hist_fp), 0) < 0)
+			perror("nstat: ftruncate");
 		rewind(hist_fp);
 
 		json_output = 0;

misc/ss.c

@@ -528,7 +528,8 @@ static void user_ent_hash_build(void)
 				snprintf(tmp, sizeof(tmp), "%s/%d/stat",
 					root, pid);
 				if ((fp = fopen(tmp, "r")) != NULL) {
-					fscanf(fp, "%*d (%[^)])", p);
+					if (fscanf(fp, "%*d (%[^)])", p) < 1)
+						; /* ignore */
 					fclose(fp);
 				}
 			}
@@ -660,7 +661,10 @@ static int get_slabstat(struct slabstat *s)
 
 	cnt = sizeof(*s)/sizeof(int);
 
-	fgets(buf, sizeof(buf), fp);
+	if (!fgets(buf, sizeof(buf), fp)) {
+		fclose(fp);
+		return -1;
+	}
 	while(fgets(buf, sizeof(buf), fp) != NULL) {
 		int i;
 		for (i=0; i<sizeof(slabstat_ids)/sizeof(slabstat_ids[0]); i++) {
@@ -2725,7 +2729,10 @@ static int unix_show(struct filter *f)
 
 	if ((fp = net_unix_open()) == NULL)
 		return -1;
-	fgets(buf, sizeof(buf)-1, fp);
+	if (!fgets(buf, sizeof(buf)-1, fp)) {
+		fclose(fp);
+		return -1;
+	}
 
 	if (memcmp(buf, "Peer", 4) == 0)
 		newformat = 1;
@@ -3210,7 +3217,10 @@ static int netlink_show(struct filter *f)
 
 	if ((fp = net_netlink_open()) == NULL)
 		return -1;
-	fgets(buf, sizeof(buf)-1, fp);
+	if (!fgets(buf, sizeof(buf)-1, fp)) {
+		fclose(fp);
+		return -1;
+	}
 
 	while (fgets(buf, sizeof(buf)-1, fp)) {
 		sscanf(buf, "%llx %d %d %x %d %d %llx %d",