From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from touchtunes.com (vantr.touchtunes.com [192.168.0.138]) by mail.touchtunes.com (Postfix) with ESMTP id 5ECA4153E3 for ; Mon, 8 Dec 2003 09:41:45 -0500 (EST) Message-ID: <3FD48E06.5050303@touchtunes.com> Date: Mon, 08 Dec 2003 09:43:18 -0500 From: Tristan Van Berkom MIME-Version: 1.0 Subject: How to share large portions of memory with user land Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: linux-mm@kvack.org List-ID: Hello all, This is one of those "How do I ..." questions which I asked at the LKML and got no response; Maybe my MM sub-system related question is better targeted here. I did my homework and all the info I could find is pretty old (dating from kernel 2.2.x) so I was hoping to be brought up-to-speed in regards to io buffers and current memory sharing techniques. My question is already well phrased and andswered in an email archived from a few years ago: http://www.ussg.iu.edu/hypermail/linux/kernel/0005.2/0505.html Andi > The traditional linux way is to implement mmap for Andi > your character device, vmalloc the memory in kernel Andi > and supply it to the user process via mmap. That means (I'm not mistaken) that first you use vmalloc to allocate a contiguous virtual memory region and suply a `nopage' method (via mmap) which returns the physical page coresponding to user's _and_ the module's virtual address plane; that means that after mucking about with page tables a while; you have two virtual contiguous memory regions (one user/one kernel) that both access the same physical scattered pages. ... ( ?? hmmm ??) Andi > 2.3 and some patched 2.2 kernels also offer a way to do this Andi > directly (usion kiovecs and map_user_kiobuf()). This is not in Andi > standard 2.2 kernel though. This approach basicly save's me from the `nopage' aspect of the afore mentioned method; but I dont have a contiguous memory region in kernel space; only in user land. Linus > Basically, the way kio buffers work is that Linus > they are 100% based on only physical pages. There are no virtual Linus > issues at all in the IO, and that's exactly how I want it. There Linus > is no reason to confuse virtual addresses into this, because the Linus > thing should be usable even in the complete absense of virtual Linus > mappings (ie the kernel can do direct IO purely based on pages - Linus > think sendfile() etc). After reading that (above quoted from...): (http://www.ussg.iu.edu/hypermail/linux/kernel/0010.2/0338.html) I can understand why. So If I have a collection of physical pages in a kio buffer is there a way to create a contigous virtual memory region out of that ? ie: unsigned long kmap_kiovec(int nr, struct kiobuf *iovec[]); Must it be done by modifying the page tables by hand ? (If so; is "linux" interrested in such an api as kmap_kiovec or is it total nonsence ?) Is there a preferred way to do this (mmap -> nopage vs. map_user_kiobuf()) ? Best regards, -Tristan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org