2008-12-15 04:52:44     mmap and __get_free_page

2008-12-15 04:52:44     mmap and __get_free_page

Daniele Pagani (ITALY)

Message: 66709   

Dear sirs,

I'm adding the mmap feature to a driver.

I start from:

http://docs.blackfin.uclinux.org/doku.php?id=mmap

but I need some suggestions about a problem.

My idea is to allocate a page of memory and then mmap this page in user space.

In simple_open I add:

// global

char *kbuf;

// in simple_open

kbuf=(char*)__get_free_page(GFP_DMA); // does __get_free_page return physical or virtual address?

if(!kbuf) return -ENOMEM;

printk("kbuf %p page_size %d\n",kbuf,(int)PAGE_SIZE);

Then, in simple_release

__free_page((unsigned long)kbuf

When I run the user space application I can see:

kbuf 0378b000 page_size 4096 // Ezkit BF537

Now, in simple_remap_mmap

static int simple_remap_mmap(struct file *filp,struct vm_area_struct *vma){

unsigned long simple_region_start;

unsigned long simple_regions_size;

unsigned long off;

unsigned long physical;

unsigned long vsize;

unsigned long psize;

int ret;

simple_region_size=PAGE_SIZE; // 4k

simple_region_start=(unsigned long)kbuf; // physical address?

off=vma->vm_pgoff<<PAGE_SHIFT;

physical=simple_region_start+off;

vsize=vma->vm_end-vma->vm_start;

psize=simple_region_size-off;

if(vsize>psize)return -EINVAL;

vma->vm_flags|=VM_MAYSHARE;

printk("remap_pfn_range(%p,0x%lx,0x%lx,0x%lx,0x%lx)\n",vma,vma->vm_start,vma->vm_pgoff,vsize,vma->vm_page_prot);

vma->vm_start=__va(simple_region_start); // this is for debug, because I don't understand exactly the matter

vma->vm_end=vma->vm_start+simple_region_size;

printk("remap_pfn_range(%p,0x%lx,0x%lx,0x%lx,0x%lx)\n",vma,vma->vm_start,vma->vm_pgoff,vsize,vma->vm_page_prot);

ret=remap_pfn_range(vma,vma->vm_start,physical,vsize,vma->vm_page_prot);

vma->vm_ops=&simple_remap_vm_ops;

simple_vma_open(vma);

return 0;

}

Then, in user space:

...

p=mmap(NULL,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE,fd,0);

if(p==MAP_FAILED)...

printf("mmap device ok p=%p\n",p);

I have as result:

kbuf 0378f000 page_size 4096

remap_pfn_range(037a4ea0,0x0,0x0,0x1000,0x0)

remap_pfn_range(037a4ea0,0x378f000,0x0,0x1000,0x0)

Simple VMA open, virt 0 , phys 0

mmap device ok p = (nil)

Simple VMA close

So, I don't understand exactly why I have p as null pointer.

Thank you in advanced for your cooperation.

Regards,

Daniele.