Add a safe wrapper for write and fix some warnings

1. Add a function writeall and make swrite wrap that function. Use either writeall or swrite, depending on whether we want to exit on errors or not.
2. Fix warnings when compiling with a higher optimisation level.
(CFLAGS ?= -pipe -O3 -march=native -mtune=native -freorder-blocks-and-partition)

Signed-off-by: hwangcc <hwangcc@csie.nctu.edu.tw>

src/util.c

@@ -265,25 +265,13 @@ char *store_restart_layout(void) {
         return NULL;
     }
 
-    size_t written = 0;
-    while (written < length) {
-        int n = write(fd, payload + written, length - written);
-        /* TODO: correct error-handling */
-        if (n == -1) {
-            perror("write()");
-            free(filename);
-            close(fd);
-            return NULL;
-        }
-        if (n == 0) {
-            DLOG("write == 0?\n");
-            free(filename);
-            close(fd);
-            return NULL;
-        }
-        written += n;
-        DLOG("written: %zd of %zd\n", written, length);
+    if (writeall(fd, payload, length) == -1) {
+        ELOG("Could not write restart layout to \"%s\", layout will be lost: %s\n", filename, strerror(errno));
+        free(filename);
+        close(fd);
+        return NULL;
     }
+
     close(fd);
 
     if (length > 0) {