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

[<binoy.jayan@xxxxxxxxx>]

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

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From: kernelnewbies-bounces@xxxxxxxxxxxxxxxxx [kernelnewbies-bounces@xxxxxxxxxxxxxxxxx] on behalf of Yu Bi [lazysmartegg@xxxxxxxxx]
Sent: Tuesday, December 31, 2013 8:05 AM
To: kernelnewbies@xxxxxxxxxxxxxxxxx
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)?

On Thu, Dec 26, 2013 at 3:42 PM, Yu Bi <lazysmartegg@xxxxxxxxx> 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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