Fix gcc fortify source warnings

Resolve issues uncovered by -D_FORTIFY_SOURCE=2, the default redhat
macro's file adds this option to the cflags.  This causes warnings
of the following type designed to keep the developer honest:

        warning: ignoring return value of 'foo', declared
                 with attribute warn_unused_result

The short term fix is to wrap these calls in VERIFY() to check the
return code.  The code was already assusing these would never fail.

Signed-off-by: Brian Behlendorf <[email protected]>

cmd/zdb/zdb.c

@@ -1668,7 +1668,7 @@ dump_uberblock(uberblock_t *ub, const char *header, const char *footer)
 {
 	time_t timestamp = ub->ub_timestamp;
 
-	(void) printf(header ? header : "");
+	(void) printf("%s", header ? header : "");
 	(void) printf("\tmagic = %016llx\n", (u_longlong_t)ub->ub_magic);
 	(void) printf("\tversion = %llu\n", (u_longlong_t)ub->ub_version);
 	(void) printf("\ttxg = %llu\n", (u_longlong_t)ub->ub_txg);
@@ -1680,7 +1680,7 @@ dump_uberblock(uberblock_t *ub, const char *header, const char *footer)
 		sprintf_blkptr(blkbuf, &ub->ub_rootbp);
 		(void) printf("\trootbp = %s\n", blkbuf);
 	}
-	(void) printf(footer ? footer : "");
+	(void) printf("%s", footer ? footer : "");
 }
 
 static void
@@ -2554,7 +2554,7 @@ zdb_dump_block_raw(void *buf, uint64_t size, int flags)
 {
 	if (flags & ZDB_FLAG_BSWAP)
 		byteswap_uint64_array(buf, size);
-	(void) write(1, buf, size);
+	VERIFY(write(fileno(stdout), buf, size) == size);
 }
 
 static void

cmd/ztest/ztest.c

@@ -2592,7 +2592,7 @@ grow_vdev(vdev_t *vd, void *arg)
 		return (vd);
 
 	fsize = lseek(fd, 0, SEEK_END);
-	(void) ftruncate(fd, *newsize);
+	VERIFY(ftruncate(fd, *newsize) == 0);
 
 	if (zopt_verbose >= 6) {
 		(void) printf("%s grew from %lu to %lu bytes\n",
@@ -5459,7 +5459,8 @@ main(int argc, char **argv)
 	process_options(argc, argv);
 
 	/* Override location of zpool.cache */
-	(void) asprintf((char **)&spa_config_path, "%s/zpool.cache", zopt_dir);
+	VERIFY(asprintf((char **)&spa_config_path, "%s/zpool.cache",
+	    zopt_dir) != -1);
 
 	/*
 	 * Blow away any existing copy of zpool.cache

lib/libzpool/kernel.c

@@ -796,7 +796,7 @@ umem_out_of_memory(void)
 {
 	char errmsg[] = "out of memory -- generating core dump\n";
 
-	write(fileno(stderr), errmsg, sizeof (errmsg));
+	(void) fprintf(stderr, "%s", errmsg);
 	abort();
 	return (0);
 }