linux-kernel - Re: [RFC PATCH v2 00/10] Add configurable block device LED triggers

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Date:   Tue, 10 Aug 2021 16:48:05 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Marek Behún <kabel@...nel.org>
Cc:     axboe@...nel.dk, kernelnewbies@...nelnewbies.org,
        Ian Pilcher <arequipeno@...il.com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        pavel@....cz, pali@...nel.org, hch@....de,
        linux-leds@...r.kernel.org
Subject: Re: [RFC PATCH v2 00/10] Add configurable block device LED triggers

On Tue, Aug 10, 2021 at 03:38:40PM +0200, Marek Behún wrote:
> On Tue, 10 Aug 2021 08:35:08 +0200
> Greg KH <gregkh@...uxfoundation.org> wrote:
> 
> > On Mon, Aug 09, 2021 at 06:50:44PM -0500, Ian Pilcher wrote:
> > > On 8/9/21 5:43 PM, Marek Behún wrote:  
> > > > I confess that I am not very familiar with internal blkdev API.  
> > > 
> > > It's mainly a matter of symbol visibility.  See this thread from a few
> > > months ago:
> > > 
> > >   https://www.spinics.net/lists/linux-leds/msg18244.html
> > > 
> > > Now ... my code currently lives in block/, so there isn't actually
> > > anything technically preventing it from iterating through the block
> > > devices.
> > > 
> > > The reactions to Enzo's patch (which you can see in that thread) make me
> > > think that anything that iterates through all block devices is likely to
> > > be rejected, but maybe I'm reading too much into it.
> > > 
> > > 
> > > Greg / Christoph -
> > > 
> > > (As you were the people who expressed disapproval of Enzo's patch to
> > > export block_class and disk_type ...)
> > > 
> > > Can you weigh in on the acceptability of iterating through the block
> > > devices (searching by name) from LED trigger code within the block
> > > subsystem (i.e. no new symbols would need to be exported)?
> > > 
> > > This would allow the trigger to implement the sysfs API that Marek and
> > > Pavel want.  
> > 
> > No idea, let's see the change first, we can never promise anything :)
> 
> Hi Greg,
> 
> Can't we use blkdev_get_by_path() (or blk_lookup_devt() with
> blkdev_get_by_dev())?
> This would open the block device and return a struct block_device *.
> When the LED trigger is disabled, it would also have to release the
> device.

But what about when the device is removed from the system first?  Be
careful about that...

Anyway, sure, try those functions, I really do not know, all I
originally complained about was those exports which did not need to be
exported.

thanks,

greg k-h