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vfs read write example

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zeroway
2017-10-21 21:47:48 +00:00
parent 3bdddf5118
commit 0cf402ced0
3 changed files with 103 additions and 1 deletions
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1
debug/char/char_skeleton_drv.c
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@ -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

36
debug/misc/Makefile Normal file
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# 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

67
debug/misc/vfs_rw.c Normal file
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#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");