Re: locking pages in memory, mapping memory

Stephen Williams (steve@icarus.com)
Mon, 01 Mar 1999 14:00:01 -0800

> 1. I would like to map a buffer from user address space to kernel address
> space, so that a user application can write data to this buffer
> and the kernel than can read this data WITHOUT having to copy
> it from user to kernel space (and vice versa)

alan@lxorguk.ukuu.org.uk said:
> You want to map a buffer in kernel address space into user address
> space, same effect but its a whole lot easier, and they are implicitly
> locked

> The sound drivers do exactly this for one example.

I also do this for fast scanner interface boards that we do. Works real
well, and has the additional advantage that funky alignment problems
do not occur.

(After all, you do not want to copy the JPEG of a 300DPI 9"x12" grayscale
image using copy_to_user if you can at all avoid it. Especially if you
get 4 of them every second.)

-- 
Steve Williams                "The woods are lovely, dark and deep.
steve@icarus.com              But I have promises to keep,
steve@picturel.com            and lines to code before I sleep,
http://www.picturel.com       And lines to code before I sleep."






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