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.
Usman
--- David Stroupe <dstroupe@keyed-upsoftware.com> wrote:
> Usman S. Ansari wrote:
>
> >No kernel is.
> >
> >--- David Stroupe <dstroupe@keyed-upsoftware.com> wrote:
> >
> >>Usman S. Ansari wrote:
> >>
> >>>When user process calls mmap system call, this address is setup by the kernel along with
> size,
> >>>this I figure is setup in some suitable place in the user process virtual space.
> >>>
> >>>Usman
> >>>
> >>But since I am the device driver writer, I am responsible for
> >>this...correct?
> >>
> So, within my user program I do something like this: void* addy =
> mmap(.....) system call. The returned variable addy can now be used in
> a call to my driver as the virtual address in a remap_page_range. Of
> course, this remap call would use the same size buffer etc. Once this
> is completed, accesses to the buffer pointed to by addy will access the
> physical memory used in my remap call?
>
> Thanks again
>
> --
> Best regards,
> David Stroupe
> Keyed-Up Software
>
>
=====
Usman S. Ansari
Linux OS & Device Drivers
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