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

[Michael Sabolish <sabolish@me.com>]

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))


> On Jan 14, 2019, at 4:30 AM, Jan Kara <jack@suse.cz> wrote:
> 
> On Mon 14-01-19 13:00:23, Pali Rohár wrote:
>> On Monday 14 January 2019 11:30:11 Jan Kara wrote:
>>>> As for the case of remounting as rw if the UDF is ro but the device is
>>>> rw, I am not sure what the best idea is to deal with this.  If this new
>>>> behavior doesn't count as a regression, is there any way to end up with a
>>>> UDF filesystem as specced by the command above (-m dvd -b 512, so with it
>>>> being read-only), but still allow for mounting it as rw if the device
>>>> supports it? Does udftools offer a way to manipulate the UDF partition
>>>> descriptor flag in a pre-existing filesystem after it had already been
>>>> created that I am missing?
>>> 
>>> So I would really prefer to keep the behavior of disallowing remounting
>>> read-only partition read write. After all ECMA-167 standard is pretty clear
>>> on this saying that for read-only partitions no sectors can be recorded. I
>>> understand it is inconvenient if you try to create e.g. a DVD image. So you
>>> want partition to be read-only in the end but initially you need it to be
>>> writeable so that you can fill-in the contents.
>>> 
>>> Generally I think a clean solution for this is to provide a way in udftools
>>> to switch partition read-only / read-write. Also this is how similar things
>>> are achieved for other filesystems. Pali, is there a way to switch
>>> accessType of a partition on existing media with udftools? If not, can you
>>> look into implementing that please? It should be rather straightforward,
>>> the biggest question really is which tool should do this...
>> 
>> You are not the first who asked for such functionality in udftools.
>> Michael (CCed) already experimented with such thing and "hacked"
>> udflabel to switch access type from overwritable to readonly.
>> 
>> I'm not against adding a new tool into udftools project which can
>> manipulate UDF access type. Question is design / API of such tool.
>> 
>> Currently udftools has udfinfo tool which prints lot of information
>> about UDF filesystem (including access type). But the only tool which
>> modifies UDF filesystem in udftools is udflabel. And udflabel is not
>> really the proper place for changing access type.
>> 
>> So some new tool for modifying UDF filesystem would be better. Which
>> other settings of UDF filesystem could be useful to be modifiable? I'm
>> thinking about "udftune" where new features for modification could be
>> implemented later too.
> 
> Yes, that sounds good to me and is in line with what tools for other
> filesystems have.
> 
> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR