From owner-freebsd-fs  Mon Mar 27  4:39:50 2000
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Date: Mon, 27 Mar 2000 07:35:36 -0500 (EST)
From: Kenneth W Cochran <kwc@world.std.com>
Message-Id: <200003271235.HAA09498@world.std.com>
To: freebsd-fs@freebsd.org
Subject: Re: ext2fs optional features
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>From krentel@dreamscape.com  Fri Mar 24 22:14:21 2000
>Date: Fri, 24 Mar 2000 22:10:50 -0500 (EST)
>To: freebsd-fs@FreeBSD.ORG
>Subject: ext2fs optional features
>Cc: kwc@world.std.com
>
>This question was asked in -stable a couple days ago, but it
>really belongs in -fs.

Ok...

>Recently, some changes were made to the ext2fs support that
>prohibit R/W mounts for some newer ext2fs partitions with
>optional features.  I've seen this with Red Hat 6.1 and
>Slackware 7.  Red Hat 6.0 seems to use an older format.

Check.  Slackware 7 in my case.  Ext2 filesystems made with
Slackware 4 appear to do ok with FreeBSD's ext2 support.

>This is what Linux's tune2fs reports:

Hmmm, which distribution/kernel version?

>   # tune2fs -l /dev/sdb2
>   tune2fs 1.15, 18-Jul-1999 for EXT2 FS 0.5b, 95/08/09
>   Filesystem volume name:   <none>
>   Last mounted on:          <not available>
>   Filesystem UUID:          38a27662-0012-11d4-8f7a-ead76bc87798
>   Filesystem magic number:  0xEF53
>   Filesystem revision #:    1 (dynamic)
>   Filesystem features:      sparse_super
>   Filesystem state:         not clean
>   Errors behavior:          Continue
>   Filesystem OS type:       Linux
>   ...
>
>And this is what appears in the logs:
>
>   Mar 24 21:36:47 blue /kernel: WARNING: R/W mount of dev 0x3040a
>   denied due to unsupported optional features

Yep.  That's what I get too.  FreeBSD 3.4-stable (about a week
"old" now) trying to access Linux (Slackware 7.0) ext2 filesystems.

>What are the optional features?  What does "sparse_super" do?
>Does Linux actually use these features, or are they for future use?
>
>Is it possible to support R/W mounts with these features?
>
>I remember 3.4-release let me mount the same filesystem R/W.
>Was I unknowingly corrupting the filesystem, or running some
>risk of a panic?
>
>I noticed that tune2fs also reported:
>
>   Block size:               4096
>   Fragment size:            4096
>
>Does Linux really not support fragments??  I was stunned.
>
>Much thanks for any answers.
>
>--Mark Krentel

To Mark's questions I might add:

(Most likely a Linux question...)
Is there a way, perhaps in Linux with its tunefs, to adjust or
"turn off" those "optional features" (other things too?) in such
a way that FreeBSD's ext2 support will work?

In other words, what would be an "optimal filesystem config" in
Linux for FreeBSD's use?

-kc


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