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

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Message-ID: <1aeb551f-827e-4e4d-b373-c6f9901a798e@postn.eu>
Date:   Mon, 14 Jan 2019 17:26:45 +0100
From:   Kevin Weidemann <kwe-lnx@...tn.eu>
To:     Pali Rohár <pali.rohar@...il.com>
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 at 16:12 Pali Rohár wrote:
> 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.

Hi Pali,

thanks for your pointers.
Interestingly enough, I chose that combination based on my test that
resulted in all (to me) relevant OSes (various Windows variants and my
set of Linux boxes) handling the resulting file system the way I
expected them to.
Choosing the bigger size of 2048 resulted in either issues when mounting
on Windows and/or having to pass a specific block size when mounting
under Linux, if I remember it correctly. It might have to do with the
block size of the block device under it. I think the point of using `-m
dvd` was to make the file system mount as read-only by default, though
it's been some months. I do remember checking what exactly `-m dvd` did
other than setting the access-type of the fs, but I must admit I don't
remember the result of that.

The main issue is, however, unaffected by this. I do agree that a
tune2fsque sort of tool as part of udftools would greatly improve the
situation.