linux-kernel - Re: [PATCH] drivers/cdrom: improved ioctl for media change detection

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Message-ID: <dc87e72b-4eea-a055-1da9-fe6e6c08a2e3@lumip.de>
Date:   Thu, 26 Aug 2021 21:01:19 +0300
From:   Lukas Prediger <lumip@...ip.de>
To:     axboe@...nel.dk
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/cdrom: improved ioctl for media change detection

On 05.08.21 22:44, Lukas Prediger wrote:
> The current implementation of the CDROM_MEDIA_CHANGED ioctl relies on
> global state, meaning that only one process can detect a disc change
> while the ioctl call will return 0 for other calling processes afterwards
> (see bug 213267 ).
>
> This introduces a new cdrom ioctl, CDROM_TIMED_MEDIA_CHANGE, that
> works by maintaining a timestamp of the last detected disc change instead
> of a boolean flag: Processes calling this ioctl command can provide
> a timestamp of the last disc change known to them and receive
> an indication whether the disc was changed since then and the updated
> timestamp.
>
> I considered fixing the buggy behavior in the original
> CDROM_MEDIA_CHANGED ioctl but that would require maintaining state
> for each calling process in the kernel, which seems like a worse
> solution than introducing this new ioctl.
>
> Signed-off-by: Lukas Prediger <lumip@...ip.de>
> ---
> This is my first patch sent to the kernel and I followed the recommended
> process as closely as I could. If I misstepped somewhere, please let me know.
> I also tried to find a mailing list more specific to the problem but was unable,
> please inform me if there is one where this should be sent instead.
>
> Finally, I wasn't sure whether/how to add my name to the updated docs
> and if I should update the date on them (there have been some recent commits
> that did not result in credits given to the commit author or updating
> the dates in the docs, but those did not add any new content either), so
> info in the most appropriate way would be welcome.
>
> Looking forward to your feedback.
> ---
>  Documentation/cdrom/cdrom-standard.rst      | 14 +++++-
>  Documentation/userspace-api/ioctl/cdrom.rst |  6 ++-
>  drivers/cdrom/cdrom.c                       | 56 +++++++++++++++++++--
>  include/linux/cdrom.h                       |  1 +
>  include/uapi/linux/cdrom.h                  | 15 ++++++
>  5 files changed, 86 insertions(+), 6 deletions(-)

As it has been several weeks and I haven't heard anything at all in response to this, 
I'd like to bring this to your attention once more. If something is wrong with it,
please let me know so I can fix it.
- Lukas