求助：将用户空间的虚拟地址映射到内核态的逻辑地址。
问题：
小弟正在写一个测试程序，程序的目的是用户空间的虚拟地址映射为内核空间的逻辑地址，然后内核空间的驱动程序对该内存空间直接操作，写入相应的字符串，后再由用户空间读出该字符串以验证程序的正确性。
程序的流程大概是这样的。
-----------------内核空间------------------------
驱动程序注册一个字符设备
实现iotctl调用。
ioctl将用户空间传递的虚拟地址通过进行页表查询转换为物理地址，然后再将物理地址转化为逻辑地址，后向该逻辑地址中写入“hello kmap”字符串
返回
-----------------用户空间------------------------
使用valloc分配一页内存
调用memset清空该内存
然后打开驱动程序注册的字符设备接口
调用字符设备的iotcl，将上述分配的一页内存的虚拟地址传递给内核驱动程序
此时内存里面应该已有驱动程序写入的字符串信息，调用printf打印该内存。
小弟按照上述思路实现了程序，但是运行以后，发生了oops。不知道问题具体出在哪里，下面贴下代码，请各位指点迷津。谢谢
---------------------------------kernel.h--------------------------------------
/*
* kernel.h 公用头文件
*/
#ifndef KMAP_KERNEL_H
#define KMAP_KERNEL_H
#ifdef KMAP_KERNEL
#define __DEBUG_MSG(a,x...) do{printk(KERN_ALERT"%s %s %d:"a,__FILE__,__FUNCTION__,__LINE__,##x);}while(0)
#else
#define __DEBUG_MSG(a,x...) do{fprintf(stderr, "%s %s %d:"a, __FILE__, __FUNCTION__, __LINE__, ##x);}while(0)
#endif
#define DEVICE_NAME "kmap"
#define KMAP_IOC_MAGIC 'q'
#define KMAP_IOC_SET_PID_AND_VADDR _IOW(KMAP_IOC_MAGIC, 1, char *)
#ifdef KMAP_KERNEL
int init_module(void);
void cleanup_module(void);
static int kmap_open(struct inode *, struct file *);
static int kmap_ioctl(struct inode *, struct file *,
unsigned int, unsigned long);
#endif
struct ioctl_arg
{
pid_t pid;
unsigned long vaddr;
};
#endif
------------------------------------kernel.c-------------------------------------
/*
*kernel.c 内核实现部分
*/
#include <linux/config.h>
#include <linux/*.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/fcntl.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/if_packet.h>
#include <linux/wireless.h>
#include <linux/kmod.h>
#include <net/ip.h>
#include <net/protocol.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <linux/errno.h>
#include <linux/timer.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/workqueue.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>
#include <linux/fs.h>
#include <linux/shm.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/hugetlb.h>
#include <linux/mman.h>
#include <linux/slab.h>
#include <linux/swapops.h>
#include <asm/io.h>
#include <asm/uaccess.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/uaccess.h>
#include <asm/cacheflush.h>
#define KMAP_KERNEL
#include "kernel.h"
static int major = 0;
static struct file_operations fops =
{
.open = kmap_open,
.ioctl = kmap_ioctl
};
int init_module(void)
{
major = register_chrdev(0, DEVICE_NAME, &fops);
if ( major < 0 )
{
printk(KERN_ALERT"register chrdev failed:%d\n", major);
return major;
}
printk(KERN_ALERT"mknod /dev/%s c %d 0\n", DEVICE_NAME, major);
return 0;
}
void cleanup_module(void)
{
/*unregister the device*/
int ret = unregister_chrdev(major, DEVICE_NAME);
if ( ret < 0 )
{
__DEBUG_MSG("Error in unregister_chrdev:%d\n", ret);
}
}
static int kmap_open(struct inode *inode, struct file *filp)
{
__DEBUG_MSG("enter kmap_open\n");
return 0;
}
static int kmap_ioctl(struct inode *inode, struct file *filp,
unsigned int cmd , unsigned long arg)
{
pid_t pid = 0;
unsigned long vaddr = 0;
unsigned long phy = 0;
unsigned long laddr = 0;
int err = 0, retval = 0;
pgd_t *pgd = NULL;
pud_t *pud = NULL;
pmd_t *pmd = NULL;
pte_t *pte = NULL;
struct page *mypage;
struct ioctl_arg k_arg;
__memset_generic(&k_arg, 0, sizeof(struct ioctl_arg));
/*get arg*/
err = !access_ok(VERIFY_READ, arg, sizeof(struct ioctl_arg));
if ( err )
{
__DEBUG_MSG("access vaild failed\n");
return -EFAULT;
}
err = copy_from_user((void *)&k_arg, (const void *)arg,
sizeof(struct ioctl_arg));
pid = k_arg.pid;
vaddr = k_arg.vaddr;
__DEBUG_MSG("pid:%d vaddr:%lu\n", pid, vaddr);
/*
*convert vaddr to kernel logic addr
*1,get the current task by pid
*2,get the phyaddr
*3,convert phyaddr to kernel logic addr
*4,write sth. in the buffer
*NOTE:step 1 is not necessay,because now current is pointed to task
*/
__DEBUG_MSG("The pid which user passed in is:%d\n"
" The current pid is:%d\n", pid, current->pid);
/*get phyaddr*/
pgd = pgd_offset(current->mm, vaddr);
if ( pgd_none(*pgd) || pgd_bad(*pgd) )
{
__DEBUG_MSG("invalid pgd\n");
retval = -1;
goto error;
}
pud = pud_offset(pgd, vaddr);
if ( pud_none(*pud) || pud_bad(*pud) )
{
__DEBUG_MSG("invalid pud\n");
retval = -1;
goto error;
}
pmd = pmd_offset(pud, vaddr);
if ( pmd_none(*pmd) || pmd_bad(*pmd) )
{
__DEBUG_MSG("invalid pmd\n");
retval = -1;
goto error;
}
__DEBUG_MSG("before pte_offset_map\n");
pte = pte_offset_map(pmd, vaddr);
__DEBUG_MSG("after pte_offset_map\n");
pte_unmap(pte);
if ( pte_none(*pte) )
{
__DEBUG_MSG("bad pte va: %X pte: %p pteval: %lX\n", vaddr, pte, pte_val(*pte));
retval = -1;
goto error;
}
phy = (pte_val(*pte)) & PAGE_MASK;
__DEBUG_MSG("the phy addr is %lu\n", phy);
mypage = pte_page(*pte);
set_bit(PG_locked, &mypage->flags);
atomic_inc(&mypage->_count);
/*convert phy to kernel logic addr*/
laddr = __pa(phy);
strcpy((char *)laddr, "hello kmap");
error:
return retval;
}
------------------------------------user.c-------------------------------------
/*
*user.c 用户空间部分
*/
#include <sys/*.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>/*getpagesize*/
#include <errno.h>
#include "kernel.h"
#define CHAR_DEV_PATH "/dev/"DEVICE_NAME
int main(int argc, char **argv)
{
int fd = -1;
pid_t pid = 0;
unsigned int vaddr = 0;
int result = 0;
int page_size =0;
struct ioctl_arg arg;
int retval = 0;
memset(&arg, 0, sizeof(struct ioctl_arg));
/*get page size*/
page_size = getpagesize();
/*get pid*/
pid = getpid();
vaddr = (unsigned long)valloc(page_size);
memset((char *)vaddr, 0, page_size);
strcpy((char *)vaddr, "hello kmap");
/*assemble arg*/
__DEBUG_MSG("The pid and the vaddr is:%d, %lu\n", pid, vaddr);
arg.pid = pid;
arg.vaddr = vaddr;
/*open the device*/
fd = open(CHAR_DEV_PATH, O_RDWR);
if ( fd < 0 )
{
__DEBUG_MSG("error when open device file:%s\n", strerror(errno));
retval = -1;
goto error;
}
/*pass the arg to kernel*/
result = ioctl(fd, KMAP_IOC_SET_PID_AND_VADDR, &arg);
if ( result )
{
__DEBUG_MSG("error when ioctl:%s\n", strerror(errno));
}
printf("after ioctl we get the memory:%s\n", (char *)vaddr);
error:
if ( fd != -1 )
{
close(fd);
}
return retval;
}
请大家重点看一下下面的代码片断，问题应该是出在这里的
/*
*convert vaddr to kernel logic addr
*1,get the current task by pid
*2,get the phyaddr
*3,convert phyaddr to kernel logic addr
*4,write sth. in the buffer
*NOTE:step 1 is not necessay,because now current is pointed to task
*/
__DEBUG_MSG("The pid which user passed in is:%d\n"
" The current pid is:%d\n", pid, current->pid);
/*get phyaddr*/
pgd = pgd_offset(current->mm, vaddr);
if ( pgd_none(*pgd) || pgd_bad(*pgd) )
{
__DEBUG_MSG("invalid pgd\n");
retval = -1;
goto error;
}
pud = pud_offset(pgd, vaddr);
if ( pud_none(*pud) || pud_bad(*pud) )
{
__DEBUG_MSG("invalid pud\n");
retval = -1;
goto error;
}
pmd = pmd_offset(pud, vaddr);
if ( pmd_none(*pmd) || pmd_bad(*pmd) )
{
__DEBUG_MSG("invalid pmd\n");
retval = -1;
goto error;
}
__DEBUG_MSG("before pte_offset_map\n");
pte = pte_offset_map(pmd, vaddr);
__DEBUG_MSG("after pte_offset_map\n");
pte_unmap(pte);
if ( pte_none(*pte) )
{
__DEBUG_MSG("bad pte va: %X pte: %p pteval: %lX\n", vaddr, pte, pte_val(*pte));
retval = -1;
goto error;
}
phy = (pte_val(*pte)) & PAGE_MASK;
__DEBUG_MSG("the phy addr is %lu\n", phy);
mypage = pte_page(*pte);
set_bit(PG_locked, &mypage->flags);
atomic_inc(&mypage->_count);
/*convert phy to kernel logic addr*/
laddr = __pa(phy);
strcpy((char *)laddr, "hello kmap");
解答（1）
我找到问题所在了。
用__va代替__pa
将物理地址转化为内核的逻辑地址是用__va而不是__pa，改动以后程序工作正常。
解答（2）
用mmap()的方法。
为你的设备file_operations定义一个mmap函数，
然后用户态调用系统调用mmap()把设备分配的内存映射到用户态，
文章来源CU社区：求助：将用户空间的虚拟地址映射到内核态的逻辑地址。
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