From owner-freebsd-fs  Fri Mar 24 19:11:57 2000
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Date: Fri, 24 Mar 2000 22:10:50 -0500 (EST)
From: "Mark W. Krentel" <krentel@dreamscape.com>
Message-Id: <200003250310.WAA00537@dreamscape.com>
To: freebsd-fs@FreeBSD.ORG
Subject: ext2fs optional features
Cc: kwc@world.std.com
Sender: owner-freebsd-fs@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.org

This question was asked in -stable a couple days ago, but it really
belongs in -fs.

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.

This is what Linux's tune2fs reports:

   # 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

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


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