Linux Kernel Homework---/proc/mtest

Memory Management

1.listvma

static void Mtest_dump_vma_list (void)

{

struct Task_struct *task = current; Get the task_struct of the current process

struct Mm_struct *mm = task->mm;

struct Vm_area_struct *vma; Get the VMA area of the current process

int count = 0; The number of VMA

Down_read (&mm->mmap_sem);

for (VMA = mm->mmap; vma; VMA = vma->vm_next)

{

count++;

PRINTK ("%d:0x%lx 0x%lx", Count, Vma->vm_start, vma->vm_end);

if (Vma->vm_flags & Vm_read)

PRINTK ("R");

Else

PRINTK ("-");

if (Vma->vm_flags & Vm_write)

PRINTK ("w");

Else

PRINTK ("-");

if (Vma->vm_flags & Vm_write)

PRINTK ("X");

Else

PRINTK ("-");

PRINTK ("\ n");

}

Up_read (&mm->mmap_sem);

}

2.findpage Addr

static struct page *

My_follow_page (struct vm_area_struct *vma, unsigned long addr)

{

pgd_t *PGD;

pmd_t *PMD;

pud_t *pud;

pte_t *pte;

spinlock_t *PTL;

struct page *page = NULL;

struct Mm_struct *mm = vma->vm_mm;

PGD = Pgd_offset (mm, addr); Get PGD

if (Pgd_none (*PGD) | | Unlikely (Pgd_bad (*PGD)))

Goto out;

PUD = Pud_offset (PGD, addr); Get PUD

if (Pud_none (*pud) | | Unlikely (Pmd_bad (*pud)))

Goto out;

PMD = Pmd_offset (pud, addr); Get PMD

if (Pmd_none (*PMD) | | Unlikely (Pmd_bad (*PMD)))

Goto out;

Pte = Pte_offset_map_lock (mm, PMD, addr, &PTL); Get Pte

if (!PTE)

Goto out;

if (!pte_present (*pte))//pte not in memory

goto unlock;

page = Pfn_to_page (PTE_PFN (*pte));

if (!page)

goto unlock;

Get_page (page);

Unlock

Pte_unmap_unlock (Pte, PTL);

Out

return page;

}

static void Mtest_find_page (unsigned long addr)

{

struct Vm_area_struct *vma;

struct Task_struct *task = current;

struct Mm_struct *mm = task->mm;

unsigned long kernel_addr;

struct page *page;

Down_read (&mm->mmap_sem);

VMA = FIND_VMA (mm, addr);

page = My_follow_page (VMA, addr);

if (!page)

{

PRINTK ("translation failed.\n");

Goto out;

}

KERNEL_ADDR = (unsigned long) page_address (page);

Kernel_addr + = (addr & ~page_mask);

PRINTK ("VMA 0X%LX, PMA 0x%lx\n", addr, kernel_addr);

Out

Up_read (&mm->mmap_sem);

}

3.writeval addr Val

static void

Mtest_write_val (unsigned long addr, unsigned long val)

{

struct Vm_area_struct *vma;

struct Task_struct *task = current;

struct Mm_struct *mm = task->mm;

struct page *page;

unsigned long kernel_addr;

Down_read (&mm->mmap_sem);

VMA = FIND_VMA (mm, addr);

Test if it is a legal VMA

if (VMA && addr >= vma->vm_start && (addr + sizeof (val)) < Vma->vm_end)

{

if (! ( Vma->vm_flags & Vm_write)//test If we have rights to WRITE

{

PRINTK ("Cannot write to 0x%lx\n", addr);

Goto out;

}

page = My_follow_page (VMA, addr);

if (!page)

{

PRINTK ("Page not found 0x%lx\n", addr);

Goto out;

}

KERNEL_ADDR = (unsigned long) page_address (page);

Kernel_addr + = (addr &~ page_mask);

PRINTK ("Write 0X%LX to Address 0x%lx\n", Val, kernel_addr);

* (unsigned long *) kernel_addr = val;

Put_page (page);

}

Else

{

PRINTK ("No VMA found for%lx\n", addr);

}

Out

Up_read (&mm->mmap_sem);

}

4.To Build a proc file

Static ssize_t

Mtest_write (struct file *file, const char __user *buffer, size_t count, loff_t *data)

{

Char buf[128];

unsigned long Val, val2;

if (Count > sizeof (BUF))

Return-einval;

if (Copy_from_user (buf, buffer, count))//get the command from Shell

Return-einval;

if (memcmp (buf, "LISTVMA", 7) = = 0)

Mtest_dump_vma_list ();

else if (memcmp (buf, "Findpage", 8) = = 0)

{

if (sscanf (buf+8, "%LX", &val) = = 1)

Mtest_find_page (Val);

}

else if (memcmp (buf, "Writeval", 8) = = 0)

{

if (sscanf (buf+8, "%lx%lx", &val, &val2) = = 2)

{

Mtest_write_val (Val, val2);

}

}

return count;

}

static struct

File_operations proc_mtest_operation = {

Write:mtest_write,

};

static int __init

Mtest_init (void)

{

Proc_create ("Mtest", 0, NULL, &proc_mtest_operation);

PRINTK ("Create mtest...\n");

return 0;

}

static void __exit

Mtest_exit (void)

{

Remove_proc_entry ("Mtest", NULL);

}

Module_license ("GPL");

Module_description ("Memory Management task");

Module_init (Mtest_init);

Module_exit (Mtest_exit);

6.some head files that should be included

#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/proc_fs.h>

#include <linux/string.h>

#include <linux/vmalloc.h>

#include <linux/init.h>

#include <linux/slab.h>

#include <linux/fs.h>

#include <linux/mm.h>

#include <linux/sched.h>

#include <linux/errno.h>

7. How to test

1) Write a Makefile

2) type ' make ' in shell

3) Type "sudo insmod Mtest.ko"

4) Type "SUDO-SU"

5) Type:echo "LISTVMA" >/proc/mtest

6) TYPE:DMESG (then you'll find a lot of VMA)

7) Choose one of them and Type:echo "findpage 0x ..." >/proc/mtest

Then TYPE:DMESG

Note:you may find, "translation failed" shows up. But that does isn't mean you fail the test. Choose an address between the start and the end of the VMA listed.

e.g. 0x123–0x345

Want to Type:echo "Findpage 0x300" >/proc/mtest

Because you cannot being sure if the beginning of the virtual address is used.

8) Choose an address so you have rights to write.

Then Type:echo "Writeval 0x ... 123 ">/proc/mtest

Type:dmesg

Note:123 can is any unsigned int

You ' d better choose the same address to test in both step 7 and 8

If the physical address is consistent.

The End.