kernelnewbies 上的一个问题，关于宏__pa的

pigjj

在kernelnewbies 邮件列表上看到的一个帖子。

In this module, i want to get the phy address for kmalloc() through page table. i think the phy address of kmalloc() is __pa(va), but when i use page
table, it does not seem the same. May be i am not fully understand the principle. Is any one can help me about this program?


#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <asm/pgtable.h>
#include <asm/page.h>

#include <linux/highmem.h>
#include <asm/kmap_types.h>


MODULE_LICENSE("GPL");

u32 ka = 0;

static int find_phy_init(void)
{
printk(KERN_ALERT "Hello in\n");

u32 kpa = 0;
pgd_t *k_pgd = NULL;
pud_t *k_pud = NULL;
pmd_t *k_pmd = NULL;
pte_t *k_pte = NULL;

ka = (u32)kmalloc(4096, GFP_KERNEL);
if(!ka)
{
printk(KERN_ALERT "kmalloc failed\n");
return 0;
}

memset(ka, 0x5a, 4096);
printk(KERN_ALERT "ka = 0x%08x\n", ka);


/* kmalloc */
k_pgd = pgd_offset_k(ka);

printk(KERN_ALERT "k_pgd = 0x%p, *k_pgd = 0x%08x\n", (u32)k_pgd, *k_pgd);

if(!pgd_none(*k_pgd))
{
k_pud = pud_offset(k_pgd, ka);
if(!pud_none(*k_pud))
{
k_pmd = pmd_offset(k_pud, ka);
printk(KERN_ALERT "k_pmd = 0x%08x, *k_pmd = 0x%08x\n", (u32)k_pmd, *k_pmd);
if(!pmd_none(*k_pmd))
{
k_pte = pte_offset_kernel(k_pmd, ka);
printk(KERN_ALERT "k_pte = 0x%08x, *k_pte = 0x%08x\n", (u32)k_pte, *k_pte);
if(!pte_none(*k_pte))
{
kpa = (pte_val(*k_pte) & PAGE_MASK) |
(ka & ~PAGE_MASK);
if(!pte_present(*k_pte))
printk(KERN_ALERT "k-page not in RAM\n");
}
else
printk(KERN_ALERT "pte is none\n");
}
}
}
if(kpa != 0)
{
printk(KERN_ALERT "k_addr 0x%08x in RAM is 0x%08x\n", ka, kpa);
printk(KERN_ALERT "__pa(k_addr) = 0x%08x\n", __pa(ka));
}


kfree((void *)ka);
return 0;
}

static void find_phy_exit(void)
{


printk(KERN_ALERT "Exit!\n");

}

module_init(find_phy_init);
module_exit(find_phy_exit);

qtdszws

你测试的结果是什么？

pigjj

[41833.279714] Hello in
[41833.279714] ka = 0xf7fd8000
[41833.279714] k_pgd = 0xc03bcf7c, *k_pgd = 0x37800163
[41833.279714] k_pmd = 0xc03bcf7c, *k_pmd = 0x37800163
[41833.279714] k_pte = 0xf7800f60, *k_pte = 0x37fd8163
[41833.279714] k_addr 0xf7fd8000 in RAM is 0x37fd8000
[41833.279714] __pa(k_addr) = 0x37fd8000

貌似是对的 ， 0xf7fd8000 是PAGE_OFFSET 开始的线性地址，减去0xc0000000,刚好是得到的物理地址0x37fd8000

Godbach

这个地方我也曾经用过，没有问题啊

Godbach

偶的这个帖子，谈到内核空间和用户空间传递数据的方式，用的是mmap。就是把内核空间申请内存的虚拟地址转为物理地址__pa(va)，然后传给用户空间，用户空间就可以通过mmap操作这块内存了。
http://linux.chinaunix.net/bbs/thread-1034670-1-1.html

emmoblin

谢谢，学习了，最近正在学习内存

Godbach

原帖由 emmoblin 于 2008-11-29 10:50 发表
谢谢，学习了，最近正在学习内存

欢迎多上论坛上交流啊