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Message-ID: <20190115084119.GE29524@quack2.suse.cz>
Date:   Tue, 15 Jan 2019 09:41:19 +0100
From:   Jan Kara <jack@...e.cz>
To:     Pali Rohár <pali.rohar@...il.com>
Cc:     Michael Sabolish <sabolish@...com>, Jan Kara <jack@...e.cz>,
        Kevin Weidemann <kwe-lnx@...tn.eu>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: udf: Prevent write-unsupported filesystem to be remounted
 read-write

On Tue 15-01-19 09:31:11, Pali Rohár wrote:
> On Monday 14 January 2019 19:07:35 Michael Sabolish wrote:
> > I can try and make a pull-request for udftune, and I can just copy the API for tune2fs.  It would work something like:
> > 
> > udftune -O read-only device            (to set read-only access type)
> > 
> > or:
> > 
> > udftune -O ^read-only device          (to clear read-only access type (aka set rw))
> 
> This API is ambiguous. What does it mean for ^read-only? In UDF you have
> following access types: overwritable, rewritable, writeonce, readonly,
> pseudo-overwritable, unknown.
> 
> So you would need to know to which R/W access type to switch
> (overwritable, rewritable, writeonce or pseudo-overwritable).
> 
> With information of media type, you could be able to guess correct
> access type. But for UDF images stored in VFS there is no media
> information. Also you can have uncommon setup, e.g. usage of CD-R
> writeonce setup on CD-R/W disc. So "autodetection" of media type would
> not work always correctly.
> 
> So I think that it would be better to have following API:
> 
>   udftune --access-type=<new_access_type>
> 
> or
> 
>   udftune --change-access-type=<new_access_type>
> 
> I understand that you would like to have similar API as tune2fs, but UDF
> settings are too different from ext*.

If you wanted to follow tune2fs interface, you can have e.g.:

udftune -E access-type=<foo>

Another question about the feature is - the access type is actually per
partition and there can be multiple partitions on UDF media. So I think we
need to specify the partition number in the command and <foo> has to
actually be something like <partition number>,<access_type>.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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