linux-kernel - Re: udf: Prevent write-unsupported filesystem to be remounted read-write

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Message-ID: <20190114151242.vrspcgld3n645qez@pali>
Date:   Mon, 14 Jan 2019 16:12:42 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Kevin Weidemann <kwe-lnx@...tn.eu>
Cc:     Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: udf: Prevent write-unsupported filesystem to be remounted
 read-write

On Monday 14 January 2019 11:30:11 Jan Kara wrote:
> On Mon 14-01-19 01:33:30, Kevin Weidemann wrote:
> > I have an issue with UDF. I used to be able to create a UDF fs in a way
> > that is very similar to this:
> > 
> > `# mkudffs --label=.... -m dvd -b 512 /dev/mapper/cryptdev1`

Hi Kevin! You should use -m dvd only in case your crtypdev1 device is
DVD. -m dvd prepares UDF filesystem layout and alignments for DVD media.

So you should not use -m dvd for hard disks.

Also DVDs have block size of 2048 bytes and UDF mandates that medium
block size matches UDF block size. Linux versions >= 4.11 do not have
problems with it, but other operating systems enforce that rule.

So you should not use -b 512 for DVD medias.

-- 
Pali Rohár
pali.rohar@...il.com