Read data of a page frame (linux) make freeze the system Post: 302353302

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Operating Systems Linux Read data of a page frame (linux) make freeze the system Post 302353302 by hahai on Tuesday 15th of September 2009 05:27:17 AM

09-15-2009

Registered User

Read data of a page frame (linux) make freeze the system

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;        
}

Last edited by hahai; 09-15-2009 at 09:47 AM..

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fsck.cramfs

FSCK.CRAMFS(8)                                                 System Administration                                                FSCK.CRAMFS(8)

NAME

       fsck.cramfs - fsck compressed ROM file system

SYNOPSIS

       fsck.cramfs [options] file

DESCRIPTION

       fsck.cramfs is used to check the cramfs file system.

OPTIONS

       -v, --verbose
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       -b, --blocksize blocksize
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       --extract[=directory]
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       -a     This option is silently ignored.

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       -V, --version
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       -h, --help
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EXIT STATUS

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SEE ALSO

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AVAILABILITY

       The  example  command  is part of the util-linux package and is available from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils
       /util-linux/>.

util-linux                                                          April 2013                                                      FSCK.CRAMFS(8)