[英]Write long to linux char device driver?
我正在嘗試在 linux 中編寫字符設備驅動程序。 不幸的是,它不適用於任何大於 255 的數字。
我希望這個驅動程序專門使用long
類型的值。 每當我輸入一個大於 255 的值時,數字就會出錯。 256 變為 0 等等。
我編寫了一個簡單的字符設備驅動程序來顯示問題,可能有很多未使用的包含語句,因為我復制了完整的驅動程序並刪除了幾乎所有內容:
圖表.c
#include <linux/init.h>
#include <linux/module.h> /* I mean this is a module after all! */
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/sched.h> /* For current task information */
#include <linux/fs.h> /* For file operations */
#include <linux/types.h> /* dev_t: device number data type */
#include <linux/cdev.h> /* cdev is the module data type that the kernel sees */
#include <asm/uaccess.h> /* For routines to copy data to/from user space */
#include <linux/uaccess.h>
#include <linux/slab.h> /* kmalloc/kfree */
MODULE_LICENSE("GPL");
#define DRIVER_NAME "chartest"
#define MAJOR_NUM 230
#define MINOR_NUM 0
struct cdev *cdev;
int test_device_open(struct inode *inode, struct file *fp) {
return 0;
}
int test_device_release(struct inode *inode, struct file *fp) {
return 0;
}
ssize_t test_read(struct file *fp, char __user *buffer, size_t count, loff_t *f_pos) {
return count;
}
ssize_t test_write(struct file *fp, const char __user *buffer, size_t count, loff_t *fpos) {
// We must validate the user's buffer and convert it to a long long
long userOperand;
unsigned char *userInput = NULL;
printk(KERN_NOTICE "Write Function Entered.\n");
printk(KERN_ALERT "Write count: %ld, Write fp: %lld\n", count, *fpos);
userInput = kmalloc(count, GFP_KERNEL);
get_user(*userInput, buffer);
printk(KERN_NOTICE "Value before cast: %ld\n", (long) *userInput);
userOperand = (long) *userInput;
printk(KERN_NOTICE "Value after cast: %ld\n", userOperand);
// Increment the file position pointer (in our case, always by 8)
*fpos += count;
kfree(userInput);
return count;
}
/*
* Declaration of function for open file operations
*/
static struct file_operations test_fops = {
.owner = THIS_MODULE,
.read = test_read,
.write = test_write,
.open = test_device_open,
.release = test_device_release,
};
// Initialization function
static int __init test_init(void)
{
// Register device number:
int err = 0;
dev_t device_number = MKDEV(MAJOR_NUM, MINOR_NUM);
err = register_chrdev_region(device_number, 1, DRIVER_NAME);
if (err < 0) {
printk(KERN_ALERT "Could not allocate device number.\n");
return err;
}
cdev = cdev_alloc();
cdev->owner = THIS_MODULE;
cdev->ops = &test_fops;
err = cdev_add(cdev, device_number, 1);
if (err) {
printk("Error allocating cdev.\n");
}
printk(KERN_ALERT "Test Initialized. Major Number: %d\n", MAJOR_NUM);
return 0;
}
// Exit function:
static void __exit test_exit(void)
{
dev_t device_number = MKDEV(MAJOR_NUM, MINOR_NUM);
// Remove char device */
cdev_del(cdev);
/* Unregister Device Number: */
unregister_chrdev_region(device_number, 1);
printk(KERN_ALERT "TestDriver %d destroyed.\n", MAJOR_NUM);
}
module_init(test_init);
module_exit(test_exit);
小測試程序:
maintest.c:
#include <unistd.h>
#include <fcntl.h>
int main(void) {
long input = 256;
int fd = open("/dev/chartest0", O_RDWR);
write(fd, &input, sizeof(long));
close(fd);
return 0;
}
printk
語句給出了以下 output ,給定輸入為 256:
Write Eunction Entered.
Write count: 8, Write fp: 0
Value before cast: 0
Value after cast: 0
給定輸入大小為 8 字節的copy_from_user
也會失敗。 當一次遍歷一個字節並復制數據時,它也會失敗。 我什么都試過了。
如果您願意提供幫助,請編譯:MakeFile
ifeq ($(KERNELRELEASE),)
# Assume the source tree is where the running kernel was built
# You should set KERNELDIR in the environment if it's elsewhere
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
# The current directory is passed to sub-makes as argument
PWD := $(shell pwd)
modules:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
modules_install:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install
clean:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions
.PHONY: modules modules_install clean
else
# called from kernel build system: just declare what our modules are
obj-m := chartest.o
endif
然后在同一目錄中:
sudo insmod chartest.ko
最后:
sudo mknod -m 777 /dev/chartest0 c 230 0
然后可以編譯maindriver.c
並運行它來測試。
有人可以幫我解決這個問題嗎?
你不能像你一樣使用get_user
:
此宏將單個簡單變量從用戶空間復制到 kernel 空間。 它支持 char 和 int 等簡單類型,但不支持結構或 arrays 等更大的數據類型。
ptr 必須具有指向簡單變量的指針類型,並且取消引用 ptr 的結果必須可分配給 x 而無需強制轉換。
使用get_user
,您只會復制第一個字符。
您需要使用copy_from_user
,這個 function 可以復制數組和結構,而不僅僅是簡單的類型:
ssize_t test_write(struct file *fp, const char __user *buffer, size_t count, loff_t *fpos) {
// We must validate the user's buffer and convert it to a long long
long userOperand;
unsigned char *userInput = NULL;
userInput = kmalloc(count, GFP_KERNEL);
printk(KERN_NOTICE "Write Function Entered.\n");
printk(KERN_ALERT "Write count: %ld, Write fp: %lld\n", count, *fpos);
/* warning, here you should test that count is exactly sizeof userInput */
copy_from_user(userInput, buffer, count);
userOperand = *(long*)userInput;
printk(KERN_NOTICE "Value after cast: %ld\n", userOperand);
// Increment the file position pointer (in our case, always by 8)
*fpos += count;
kfree(userInput);
return count;
}
您還可以在copy_from_user
中從char *
復制到long
(在這種情況下沒有 memory alloc):
ssize_t test_write(struct file *fp, const char __user *buffer, size_t count, loff_t *fpos) {
// We must validate the user's buffer and convert it to a long long
long userOperand;
printk(KERN_NOTICE "Write Function Entered.\n");
printk(KERN_ALERT "Write count: %ld, Write fp: %lld\n", count, *fpos);
/* warning, here you should test that count is exactly sizeof userOperand */
copy_from_user(&userOperand, buffer, sizeof userOperand);
printk(KERN_NOTICE "Value after reading: %ld\n", userOperand);
// Increment the file position pointer (in our case, always by 8)
*fpos += count;
return count;
}
您錯誤地使用了宏get_user
。
它的第一個參數實際上應該是一個變量名,而不是它的地址。
它的第二個參數應該是指向用戶空間數據的類型指針。 該指針的確切類型用於確定要讀取的數據的大小。
正確的:
long userOperand;
...
get_user(userOperand, (const long __user*)buffer);
printk(KERN_NOTICE "Value written: %ld\n", userOperand);
注意第二個參數的情況: read long
而不是char
需要它(因為buffer
參數是指向char
的指針)。
注意,上面的代碼沒有使用你的userInput
變量,所以你不需要定義它,也不需要分配 memory。
請注意,可以使用任何表示從用戶傳遞的字節數的count
參數調用.write
方法。 由於get_user
始終嘗試讀取預定義的字節數(在您的情況下,此數字等於long
的大小),因此檢查count
是否等於該數字(或者至少是不少於給定的數字):
if (count != sizeof(long)) {
return -EINVAL;
}
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