Re: Locking User memory pages from a driver....

[Eric Lowe]

Hello,

> How do i lock user mode memmory pages from kernel mode driver.. so that i
> can access it whenever i need to from the driver.... I am using linux kernel
> 2.2.14.. can this be done in this kernel version... or is it supported in
> some other newer versions.. like 2.4..
> 

raw I/O.  Stock in 2.4, available as a patch in 2.2.  You're in luck,
I just released an updated patch against 2.2.17 and 2.2.18preXX yesterday,
based on SCT's raw I/O and with Andrea's fixes.

http://www.donet.com/~elowe/linux/patches

For example usage see fs/block.c brw_kiovec() and drivers/char/raw.c
Basically you call:

  alloc_kiovec() to initialize kiobufs

  map_user_kiobuf() to map a kiobuf to a user buffer (best if <= 64K)

  Look in the kiobuf to get the iobuf->offset into the first page
    and addresses to the pages:

	bounce = iobuf->bouncelist[pageind];

	if (bounce)
		page = bounce;
	else
		page = iobuf->pagelist[pageind];

  The page is a kernel virtual address as an unsigned long you can
    then translate in the usual way (e.g. virt_to_bus() for PCI).
    Don't forget to count the length of the last page as
    PAGE_SIZE-iobuf->offset or you'll run over in your S/G.

  unmap_kiobuf() to unmap the kiobuf and unpin the pages

If you do a lot of DMA I/O with large buffers you'll need to apply
the 22vmfix patch in the same directory or you'll run out memory
and things will start to be OOM killed.

--
Eric Lowe
Software Engineer, Systran Corporation
[e-mail]