Hello,
I'm writing a linux driver that reading the data of a page frame of an process. But when I use it, it make immediately freeze the system. Can you help me? Thank for reading my question!
system: Ubuntu 9.04, kernel 2.6.28.15, Intel Duo
Code:
static int read_addr(int pid, unsigned long linear_addr, unsigned int n_bytes, char* buff){
/*
pid: id of process
linear_addr: linear address of memory region to be read
n_bytes: nombre bytes to be read
buff: the buffer containing the result
*/
struct task_struct *task;
struct mm_struct *mm = NULL;
pgd_t *pgd;
pmd_t *pmd;
pte_t *pte;
unsigned long pteval;
int ret = 0;
for_each_process(task) {
if ( task->pid == pid) {
mm = task->mm;
}
}
if(mm == NULL)
return 1;
spin_lock(&mm->page_table_lock);
pgd = pgd_offset(mm, linear_addr);
if (pgd_none(*pgd)) { ret = 2; goto out; }
pmd = pmd_offset(pgd, linear_addr);
if (pmd_none(*pmd)) { ret = 3; goto out; }
pte = pte_offset_map(pmd, linear_addr);
if (pte_present(*pte)){
unsigned long pteid = pte_index(linear_addr);
pteval = pte_val(*pte);
memcpy(buff, pteval + pteid, n_bytes);
} else {
ret = 4;
goto out;
}
pte_unmap(pte);
spin_unlock(&mm->page_table_lock);
return 0;
out:
printk("error: %d\n", ret);
spin_unlock(&mm->page_table_lock);
return ret;
}