From owner-freebsd-hackers  Tue Oct 21 19:30:34 1997
Return-Path: <owner-freebsd-hackers>
Received: (from root@localhost)
          by hub.freebsd.org (8.8.7/8.8.7) id TAA27547
          for hackers-outgoing; Tue, 21 Oct 1997 19:30:34 -0700 (PDT)
          (envelope-from owner-freebsd-hackers)
Received: from pluto.plutotech.com (root@mail.plutotech.com [206.168.67.137])
          by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id TAA27542
          for <hackers@FreeBSD.ORG>; Tue, 21 Oct 1997 19:30:31 -0700 (PDT)
          (envelope-from durian@plutotech.com)
Received: from shane.plutotech.com (shane.plutotech.com [206.168.67.149])
	by pluto.plutotech.com (8.8.5/8.8.5) with ESMTP id UAA15838;
	Tue, 21 Oct 1997 20:30:28 -0600 (MDT)
Message-Id: <199710220230.UAA15838@pluto.plutotech.com>
From: "Mike Durian" <durian@plutotech.com>
To: "Mike Durian" <durian@plutotech.com>
cc: hackers@FreeBSD.ORG
Subject: Re: user vm addr to kernel vm addr 
In-reply-to: Your message of "Mon, 20 Oct 1997 20:01:11 MDT."
Date: Tue, 21 Oct 1997 20:30:28 -0600
Sender: owner-freebsd-hackers@FreeBSD.ORG
X-Loop: FreeBSD.org
Precedence: bulk

On Mon, 20 Oct 1997 20:01:11 MDT, "Mike Durian" <durian@plutotech.com> wrote:
>  In my virtual file system I'd like to speed up reads and writes
>by copying directly from the uio structure to a vm address of
>a buffer in the user process running on behalf of the filesystem.
>I'm currently shoving all the data through a socket that the
>user process reads from and copies into a buffer.  I'd like to
>go direct and skip the socket writing part.  Does that make sense?
>  Anyway, I want to copy from a uio to a different process's vm space.
>I can get the vm address of the destination buffer over a socket and
>think I can use vm_fault_wire to make sure it stays accessable, but
>I don't know how to convert that user space vm address into a
>kernel space vm address that I can then use with copyout.
>  Is there an easy (or any) way to do this?

  I'm following up to my own post.  I should mention that the
user process containing the vm buffer that I want to convert is
*not* curproc.  I want to go between that buffer and a struct uio
in my VOP_READ and VOP_WRITE functions.
  I did find something that works, but perhaps someone has a
better/cleaner way of doing it.  I don't think I need to do
the vm_fault_wire either.

	for each page in the vm buffer
		vm_map_lookup	to get the vm object
		vm_page_lookup	to get the page for the object
	kmem_alloc_pageable	to allocate kernel vm space
	pmap_qenter		to map the pages into the kernel vm address
	uiomove			copy from the new kernel address to uio
	pmap_qremove		to unmap the pages
	kmem_free		to release the kernel vm space

mike