NetBSD Problem Report #55932
From martin@aprisoft.de Sat Jan 16 12:20:47 2021
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for <gnats-bugs@gnats.NetBSD.org>; Sat, 16 Jan 2021 12:20:47 +0000 (UTC)
Message-Id: <20210116122036.E8F275CC7B9@emmas.aprisoft.de>
Date: Sat, 16 Jan 2021 13:20:36 +0100 (CET)
From: martin@NetBSD.org
Reply-To: martin@NetBSD.org
To: gnats-bugs@NetBSD.org
Subject: NFS root is not read only
X-Send-Pr-Version: 3.95
>Number: 55932
>Category: kern
>Synopsis: NFS root is not read only
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: kern-bug-people
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Sat Jan 16 12:25:00 +0000 2021
>Last-Modified: Wed Jun 09 01:45:01 +0000 2021
>Originator: Martin Husemann
>Release: NetBSD 9.99.77
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD martins.aprisoft.de 9.99.77 NetBSD 9.99.77 (GENERIC) #42: Sat Jan 2 21:12:56 CET 2021 martin@martins.aprisoft.de:/usr/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
When using a read-only mount for / on a diskless client the mountall
rc.d script fails:
Mounting all file systems...
mount_nfs: emmas:/fire-below on /: Operation not supported
/etc/rc.d/mountall exited with code 1
This is with a /etc/fstab entry like:
# NetBSD /etc/fstab
# See /usr/share/examples/fstab/ for more examples.
emmas:/fire-below / nfs ro
tmpfs /tmp tmpfs rw,-sram%30
tmpfs /var tmpfs rw,-sram%30
kernfs /kern kernfs rw
ptyfs /dev/pts ptyfs rw
procfs /proc procfs rw
It seems that NFS can not downgrade from a rw to a ro mount (this is bug 1)
and the kernel NFS mountroot code seems to alread mount / as read-write
(different than all other file systems mounted as root - this is bug 2).
>How-To-Repeat:
s/a
>Fix:
n/a
>Audit-Trail:
From: mlelstv@serpens.de (Michael van Elst)
To: gnats-bugs@netbsd.org
Cc:
Subject: Re: kern/55932: NFS root is not read only
Date: Sat, 16 Jan 2021 13:51:50 -0000 (UTC)
martin@NetBSD.org writes:
>and the kernel NFS mountroot code seems to alread mount / as read-write
>(different than all other file systems mounted as root - this is bug 2).
Bug 2 seems to be intentional:
/*
* Historical practice expects NFS root file systems to
* be initially mounted r/w.
*/
mp->mnt_flag &= ~MNT_RDONLY;
--
--
Michael van Elst
Internet: mlelstv@serpens.de
"A potential Snark may lurk in every tree."
From: David Holland <dholland-bugs@netbsd.org>
To: gnats-bugs@netbsd.org
Cc:
Subject: Re: kern/55932: NFS root is not read only
Date: Wed, 9 Jun 2021 01:40:08 +0000
On Sat, Jan 16, 2021 at 01:55:01PM +0000, Michael van Elst wrote:
> >and the kernel NFS mountroot code seems to alread mount / as read-write
> >(different than all other file systems mounted as root - this is bug 2).
>
> Bug 2 seems to be intentional:
>
> /*
> * Historical practice expects NFS root file systems to
> * be initially mounted r/w.
> */
> mp->mnt_flag &= ~MNT_RDONLY;
There's no reason to mount an nfs root readonly. Mounting root
readonly is so you can fsck.
--
David A. Holland
dholland@netbsd.org
(Contact us)
$NetBSD: query-full-pr,v 1.46 2020/01/03 16:35:01 leot Exp $
$NetBSD: gnats_config.sh,v 1.9 2014/08/02 14:16:04 spz Exp $
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