Greetings,
I'm reading Rubini, p.384-5, regarding mmap() and remap_pange_range().
He references the char/mem.c device driver in the linux kernel, and using that code provides an example of phsyical memory mapping to a process virtual address. The code I'm interested in is attached to the bottom. Specifically, I'm confused as to the usage of the line of code:
/* Don't try to swap out physical pages.. */
vma->vm_flags |= VM_RESERVED;
I want to do this in my own code: map a physical device page of memory to user space, and be sure its not swapped out. What confuses me is that vma->vm_flags never seems to get used by any of char/mem.c or any or Rubini's discussion examples.
Does this code actually do anything? Can someone explain how?
Thanks alot for your interest!
Code from char/mem.c:
static int mmap_mem(struct file * file, struct vm_area_struct * vma)
{
unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
/*
* Accessing memory above the top the kernel knows about or
* through a file pointer that was marked O_SYNC will be
* done non-cached.
*/
if (noncached_address(offset) || (file->f_flags & O_SYNC))
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
/* Don't try to swap out physical pages.. */
vma->vm_flags |= VM_RESERVED;
/*
* Don't dump addresses that are not real memory to a core file.
*/
if (offset >= __pa(high_memory) || (file->f_flags & O_SYNC))
vma->vm_flags |= VM_IO;
if (remap_page_range(vma->vm_start, offset, vma->vm_end-vma->vm_start,
vma->vm_page_prot))
return -EAGAIN;
return 0;
}
________________________________________
Nat Ersoz Myrio Corporation -o)
nat.ersoz@myrio.com Cell: 425.417.5182 /\\
Phone: 425.897.7278 Fax: 425.897.5600 _\_V
3500 Carillon Point Kirkland, WA 98033
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive: http://mail.nl.linux.org/kernelnewbies/
IRC Channel: irc.openprojects.net / #kernelnewbies
Web Page: http://www.kernelnewbies.org/
