how to use mmap() on a disk file to get a kernel address?

[binoy.jayan at wipro.com]

Hi,

If you have your file data in a user space buffer, "get_user_pages" and "kmap" can be used to get it mapped to a kernel virtual address. But I still doubt that this would solve the problem of mapping the disk file data to kernel space.

Regards,
Binoy Jayan

________________________________
From: kernelnewbies-bounces at kernelnewbies.org [kernelnewbies-bounces at kernelnewbies.org] on behalf of Yu Bi [lazysmartegg at gmail.com]
Sent: Tuesday, December 31, 2013 8:05 AM
To: kernelnewbies at kernelnewbies.org
Subject: Re: how to use mmap() on a disk file to get a kernel address?

Thanks  for your idea.
Because I implement a  kernel  storage service  based on a disk file through  VFS layer.
To  simplify the implementation,  I prefer  to   read/write  the mapped kernel space address instead of the file data access api(such as page cache API / VFS API).

In FreeBSD, I can use  vm_map_find to map a file into  kernel space address( vnode pager)
But in linux,  I don't know how to implement this(map disk file into  kernel space)?
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On Thu, Dec 26, 2013 at 3:42 PM, Yu Bi <lazysmartegg at gmail.com<mailto:lazysmartegg at gmail.com>> wrote:
Hi,
   I try to mmap a file in a linux kernel module. I have tried to use the function do_mmap_pgoff. But the address returned is memory virtual address in current process' user space, i.e., below the kernel boundary. Instead, I want to map the file in the kernel space and get the kernel virtual address of the mapped region. Is there any kernel API in Linux support this operation? Or I have to reimplement a kernel mmap version ?
  But reimplement a kernel version mmap() is  not easy I guess. Do you have any idea?







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