add file read speed test.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@321 bbd45198-f89e-11dd-88c7-29a3b14d5316

examples/file/readspeed.c

+#include <rtthread.h>
+#include <dfs_posix.h>
+
+void readspeed(const char* filename, int block_size)
+{
+    int fd;
+    char *buff_ptr;
+    rt_size_t total_length;
+    rt_tick_t tick;
+
+    fd = open(filename, 0, DFS_O_RDONLY);
+    if (fd < 0)
+    {
+        rt_kprintf("open file:%s failed\n", filename);
+        return;
+    }
+
+    buff_ptr = rt_malloc(block_size);
+    if (buff_ptr == RT_NULL)
+    {
+        rt_kprintf("no memory\n");
+        close(fd);
+
+        return;
+    }
+
+    tick = rt_tick_get();
+    total_length = 0;
+    while (1)
+    {
+        int length;
+        length = read(fd, buff_ptr, block_size);
+
+        if (length == 0) break;
+        total_length += length;
+    }
+    tick = rt_tick_get() - tick;
+
+	/* close file and release memory */
+    close(fd);
+	rt_free(buff_ptr);
+
+    /* calculate read speed */
+    rt_kprintf("File read speed: %d byte/s\n", total_length/ (tick/RT_TICK_PER_SECOND));
+}
+
+#ifdef RT_USING_FINSH
+#include <finsh.h>
+FINSH_FUNCTION_EXPORT(readspeed, perform file read test);
+#endif