Usman S. Ansari wrote:
>I have a driver (this is continuation of preserving memory accross reboot) whic has some memory
>allocated and my application wants to write to it. Therefore in the application I (after open
>call) do
>
> if ((ptr = (char *) mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == NULL)
> {
> perror("error ...");
> }
>
>Now I have access to memory starting at virtual location ptr for next 4096 bytes. In my driver
>static int ocr_mmap(struct file *file, struct vm_area_struct *vma)
>{
> unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
> int minor = MINOR(file->f_dentry->d_inode->i_rdev);
>
> vma->vm_flags |= VM_RESERVED;
>
> if (offset >= __pa(high_memory) || (file->f_flags & O_SYNC))
> vma->vm_flags |= VM_IO; /* since this driver maps different kind of segs */
>
>if (remap_page_range(vma->vm_start, __pa(dT[minor].addr), vma->vm_end - vma->vm_start,
> vma->vm_page_prot) < 0)
> return -EAGAIN;
>
> return(0);
>}
>
>Following 3 are filled by kernel
>vma->vm_start
>vma->vm_end
>vma->vm_start
>
>__pa(dT[minor].addr) ---> I have a kernel virtual address and __pa() gives me physical address.
>
>I hope this is helpfull.
>
Indeed it has been, thanks...I am to this point. I have vmalloced
memory in the kernel, called mmap using the virt_to_phys call on the
address returned by vmalloc and get a zero return value from
remap_page_range. At that point, I would assume that I should be able
to access the memory using the address that was returned from the mmap
call. Using gdb, I am told that it cannot access the memory at the
address that was returned. (x /256xb address is the dgb command that I
am using). I have used the PROT_READ|PROT_WRITE as well as the
MAP_SHARED. What am I missing?
TIA
--
Best regards,
David Stroupe
Keyed-Up Software
5307 Faireast Court
Arlington, Texas 76018-1683
817/557-4903 voice
817/472-0408 fax
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