From 0cf402ced0758440bf8a86dfc3eceb1444f2bacc Mon Sep 17 00:00:00 2001
From: zeroway <M_O_Bz@163.com>
Date: Sat, 21 Oct 2017 21:47:48 +0000
Subject: [PATCH] vfs read write example

---
 debug/char/char_skeleton_drv.c |  1 -
 debug/misc/Makefile            | 36 ++++++++++++++++++
 debug/misc/vfs_rw.c            | 67 ++++++++++++++++++++++++++++++++++
 3 files changed, 103 insertions(+), 1 deletion(-)
 create mode 100644 debug/misc/Makefile
 create mode 100644 debug/misc/vfs_rw.c

diff --git a/debug/char/char_skeleton_drv.c b/debug/char/char_skeleton_drv.c
index dfa932b..c0aa522 100644
--- a/debug/char/char_skeleton_drv.c
+++ b/debug/char/char_skeleton_drv.c
@@ -7,7 +7,6 @@
 #include <linux/cdev.h>
 #include <linux/ioport.h>
 #include <linux/device.h>
-#include <linux/device.h>
 #include <asm/uaccess.h>
 
 #define CHAR_SKELETON_COUNT	1
diff --git a/debug/misc/Makefile b/debug/misc/Makefile
new file mode 100644
index 0000000..0da471c
--- /dev/null
+++ b/debug/misc/Makefile
@@ -0,0 +1,36 @@
+# Makefile
+# Comment/uncomment the following line to disable/enable debugging
+# DEBUG = y
+
+# Usage
+# make CROSS_COMPILE=<cross_compiler_prefix> KERNEL_DIR=<your_kernel_dir> KERNEL_BUID_OUTPUT=<kernel_buid_output>
+#
+# make CROSS_COMPILE=/home/zeroway/rk3399/tool/gcc-linaro-4.9.4-2017.01-i686_aarch64-linux-gnu/bin/aarch64-linux-gnu- KERNEL_DIR=/home/zeroway/rk3399/src/firefly/kernel KERNEL_BUID_OUTPUT=/home/zeroway/rk3399/src/firefly/out/target/product/rk3399_firefly_box/obj/KERNEL
+
+# Add your debugging flag (or not) to CFLAGS
+ifeq ($(DEBUG),y)
+DEBFLAGS = -O -g -DSCULL_DEBUG # "-O" is needed to expand inlines
+else
+DEBFLAGS = -O2
+endif
+
+obj-m := vfs_rw.o
+
+KERNEL_DIR ?= /lib/modules/$(shell uname -r)/build
+KERNEL_BUID_OUTPUT ?=$(KERNEL_DIR)
+CC = $(CROSS_COMPILE)gcc
+LD = $(CROSS_COMPILE)ld
+PWD := $(shell pwd)
+
+modules:
+	$(MAKE) -C $(KERNEL_DIR) ARCH=arm64 M=$(PWD) O=$(KERNEL_BUID_OUTPUT) modules
+
+clean:
+	rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions modules.order Module.symvers
+
+depend .depend dep:
+	$(CC) $(CFLAGS) -M *.c > .depend
+
+ifeq (.depend,$(wildcard .depend))
+include .depend
+endif
diff --git a/debug/misc/vfs_rw.c b/debug/misc/vfs_rw.c
new file mode 100644
index 0000000..252934d
--- /dev/null
+++ b/debug/misc/vfs_rw.c
@@ -0,0 +1,67 @@
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+
+/* read write buffer */
+static char wbuf[] = "this is a kernel read write test";
+static char rbuf[1024];
+
+#define FILE_NAME "/tmp/vfs_rw_test"
+
+/*
+ * 在内核中一般不容易生成用户空间的指针
+ * 或者不方便独立使用用户空间内存
+ * 而vfs_read,vfs_write的参数buffer都是用户空间指针
+ * 所以需要调用set_fs目的是为了让内核改变对内存地址检查的处理方式
+ * set_fs参数只有两个USER_DS和KERNEL_DS
+ * USER_DS代表用户空间,set_fs
+ * KERNEL_DS代表内核空间
+ */
+static int vfs_rw_init(void)
+{
+	struct file *fp;
+	mm_segment_t fs;
+	loff_t pos;
+
+	printk("%s, %d\n", __FUNCTION__, __LINE__);
+
+	/* open file */
+	fp = filp_open(FILE_NAME, O_RDWR | O_CREAT, 0644);
+	if (IS_ERR(fp))
+	{
+		printk("create file error\n");
+		return -1;
+	}
+
+	/* write file */
+
+	/* get current fs*/
+	fs = get_fs();
+
+	/* 即对内核空间地址检查并做变换 */
+	set_fs(KERNEL_DS);
+	pos = 0;
+	printk("=> %s\n", wbuf);
+	vfs_write(fp, wbuf, sizeof(wbuf), &pos);
+
+	/* read file */
+	pos = 0;
+	vfs_read(fp, rbuf, sizeof(wbuf), &pos);
+	printk("<= %s\n", rbuf);
+
+	/* close file */
+	filp_close(fp, NULL);
+	set_fs(fs);
+
+	return 0;
+}
+
+static void vfs_rw_exit(void)
+{
+	printk("%s, %d\n", __FUNCTION__, __LINE__);
+}
+
+module_init(vfs_rw_init);
+module_exit(vfs_rw_exit);
+MODULE_LICENSE("GPL");