From owner-cvs-all  Sat Sep 18 22:13:20 1999
Delivered-To: cvs-all@freebsd.org
Received: from proxy4.ba.best.com (proxy4.ba.best.com [206.184.139.15])
	by hub.freebsd.org (Postfix) with ESMTP
	id C76F3151F5; Sat, 18 Sep 1999 22:13:12 -0700 (PDT)
	(envelope-from dillon@apollo.backplane.com)
Received: from apollo.backplane.com ([209.157.86.2])
	by proxy4.ba.best.com (8.9.3/8.9.2/best.out) with ESMTP id WAA17533;
	Sat, 18 Sep 1999 22:12:58 -0700 (PDT)
Received: (from dillon@localhost)
	by apollo.backplane.com (8.9.3/8.9.1) id WAA68295;
	Sat, 18 Sep 1999 22:12:17 -0700 (PDT)
	(envelope-from dillon)
Date: Sat, 18 Sep 1999 22:12:17 -0700 (PDT)
From: Matthew Dillon <dillon@apollo.backplane.com>
Message-Id: <199909190512.WAA68295@apollo.backplane.com>
To: Greg Lehey <grog@lemis.com>
Cc: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG
Subject: Re: User block device access (was: cvs commit: src/sys/miscfs/specfs spec_vnops.c src/sys/sys vnode.h src/sys/kern vfs_subr.c)
References: <199909170610.XAA56084@freefall.freebsd.org> <19990919105045.T55065@freebie.lemis.com>
Sender: owner-cvs-all@FreeBSD.ORG
Precedence: bulk


:On Thursday, 16 September 1999 at 23:10:28 -0700, Matt Dillon wrote:
:> dillon      1999/09/16 23:10:28 PDT
:>
:>   Modified files:
:>     sys/miscfs/specfs    spec_vnops.c
:>     sys/sys              vnode.h
:>     sys/kern             vfs_subr.c
:>   Log:
:>       Add vfs.enable_userblk_io sysctl to control whether user reads and writes
:>       to buffered block devices are allowed.  The default is to be backwards
:>       compatible, i.e. reads and writes are allowed.
:>
:>       The idea is for a larger crowd to start running with this disabled and
:>       see what problems, if any, crop up, and then to change the default to
:>       off and see if any problems crop up in the next 6 months prior to
:>       potentially removing support entirely.  There are still a few people,
:>       Julian and myself included, who believe the buffered block device
:>       access from usermode to be useful.
:
:Add me to that list.  What reasons have been given for disabling it?
:
:Greg

    This is one of the major issues that led to the problems between Poul 
    and I which spilled over into -committers two weeks ago.  A number of
    people, including me, are not willing to allow block device access
    from usermode to be removed, at least not in the manner it was (prior
    to being backed-out).  Others make the point that nobody seems to be
    using buffered block devices anymore and that their original creation
    was a fluke anyway, so they should be removed.  You can revisit that
    thread to get a recap, I'd rather not reopen that can of worms here.

    The pseudo-compromise is to make it a sysctl and procedure that will
    determine how many people actually use buffered block devices vs raw
    devices (raw devices are obviously used and not going away).   I
    personally believe that block devices are useful.  I am willing to go
    through a process to decide the point once and for all.

    A number of problems have already been found and fixed.  For example:
    problems with savecore.  On the otherhand, there are still some problems
    which have not been fixed, such as fsck assuming a 512 byte sector size.
    fsck cannot be run on filesystems with a larger physical sector size 
    except via a buffered block device.  And nobody really knows how many
    people outside the core developers use buffered block devices for other
    purposes.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe cvs-all" in the body of the message