Subject: Re: Per-thread user <-> kernel communication area
To: Andrew Doran <>
From: Bill Stouder-Studenmund <>
List: tech-kern
Date: 11/08/2007 16:33:08
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Thu, Nov 08, 2007 at 10:41:37PM +0000, Andrew Doran wrote:
> Hi all,
> The below diff provides a wired-down, per-LWP area that is shared between=
> user process and the kernel. It's not implemented as a commpage, because I
> want to be able to send information in both directions, meaning the user
> part has to be mapped read/write. Also, one advantage to having the kernel
> allocate single blocks on behalf of the user process is that we can add to
> the block later without backward compatibility concerns.

Two comments:

1) kern_lpw.c seems to be losing a lot of DPRINTF() stuff. I think that=20
should be a separate change.

2) What thoughts do you have for versioning this stuff? Specifically, I=20
can see a utility in eventually having the app communicate some things to=
the kernel via this page. How do we avoid having either side end up=20
waiting for something the other doesn't know to do?

A sub-comment of the above, once we've added more stuff, how would we=20
handle obsoleting stuff? Say we add something then, after having actually=
tried it, realize that it's unworkable. How do we get rid of it?

Take care,


Content-Type: application/pgp-signature
Content-Disposition: inline

Version: GnuPG v1.4.7 (NetBSD)