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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 4 Jan 2023 13:32:24 -0800
Message-ID: <CAHk-=wiDdw8tRzzx=ZBzUftC1TOiOO+kxv0s8HS342BC-jzkLQ@mail.gmail.com>
Subject: Re: Linux 6.2-rc1
To:     =?UTF-8?Q?Pali_Roh=C3=A1r?= <pali@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jens Axboe <axboe@kernel.dk>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Jan 4, 2023 at 12:56 PM Pali Roh=C3=A1r <pali@kernel.org> wrote:
>
> Last time I did big retest of optical media was two years ago. At that
> time kernel was not able to mount CD-RW disc in full read-write mode
> from the normal node /dev/cdrom. Via pktcdvd driver mapping it was
> possible without any issue.

So that is part of the problem here: pretty much nobody uses optical
media any more, and the whole driver has been orphaned and has no
maintainer (for the last five years - it's why it was removed, after
all).

And people _have_ been using the normal /dev/cdrom for this, so it
almost certainly isn't entirely broken. But the test coverage is
getting increasingly sparse...

> Was there any change in last 5 (or more) years in this CD-RW area?

There's been a fair amount of cleanup wrt all the SCSI ioctl handling
in the last 5 years (and before).

But:

> Mounting CD-RW media in read-only mode via normal /dev/cdrom node
> always worked fine. Also "burning" CD-R media with userspace burning
> tools on normal /dev/cdrom node also worked.

Yeah, that's all I ever personally have done, and that most definitely
has been there for decades...

> But here it is CD-RW media in read-write mode with kernel udf
> filesystem driver without any userspace involved (after proper
> formatting).

... but I'm not sure about direct writeable mount support.

That may indeed be an area that only pktcdvd ended up doing. I've
never used it myself, even historically.

Let's bring in more people. Because they may not have thought about
some RW UDF case.

The removal seems to revert cleanly, although it does require
reverting a few subsequent commits too (that removed code that only
pktcdvd used):

    git revert db1c7d779767 85d6ce58e493 f40eb99897af

where we have

    db1c7d779767 block: bio_copy_data_iter
    85d6ce58e493 block: remove devnode callback from struct
block_device_operations
    f40eb99897af pktcdvd: remove driver.

Christoph, Jens? See

    https://lore.kernel.org/lkml/20230104190115.ceglfefco475ev6c@pali/

for the beginning of this thread.

                 Linus