fatfs: bypass newlib buffering in performance test

components/fatfs/test/test_fatfs_common.c

@@ -696,20 +696,20 @@ void test_fatfs_concurrent(const char* filename_prefix)
     vSemaphoreDelete(args4.done);
 }
 
-void test_fatfs_rw_speed(const char* filename, void* buf, size_t buf_size, size_t file_size, bool write)
+void test_fatfs_rw_speed(const char* filename, void* buf, size_t buf_size, size_t file_size, bool is_write)
 {
     const size_t buf_count = file_size / buf_size;
 
-    FILE* f = fopen(filename, (write) ? "wb" : "rb");
+    FILE* f = fopen(filename, (is_write) ? "wb" : "rb");
     TEST_ASSERT_NOT_NULL(f);
 
     struct timeval tv_start;
     gettimeofday(&tv_start, NULL);
     for (size_t n = 0; n < buf_count; ++n) {
-        if (write) {
-            TEST_ASSERT_EQUAL(1, fwrite(buf, buf_size, 1, f));
+        if (is_write) {
+            TEST_ASSERT_EQUAL(buf_size, write(fileno(f), buf, buf_size));
         } else {
-            if (fread(buf, buf_size, 1, f) != 1) {
+            if (read(fileno(f), buf, buf_size) != buf_size) {
                 printf("reading at n=%d, eof=%d", n, feof(f));
                 TEST_FAIL();
             }
@@ -723,6 +723,6 @@ void test_fatfs_rw_speed(const char* filename, void* buf, size_t buf_size, size_
 
     float t_s = tv_end.tv_sec - tv_start.tv_sec + 1e-6f * (tv_end.tv_usec - tv_start.tv_usec);
     printf("%s %d bytes (block size %d) in %.3fms (%.3f MB/s)\n",
-            (write)?"Wrote":"Read", file_size, buf_size, t_s * 1e3,
+            (is_write)?"Wrote":"Read", file_size, buf_size, t_s * 1e3,
                     file_size / (1024.0f * 1024.0f * t_s));
 }