Re: [PATCH v4 3/4] block: add support for notifications

[Daniel Golle <daniel@makrotopia.org>]

On Thu, Jun 27, 2024 at 09:45:45PM -0700, Christoph Hellwig wrote:
> On Thu, Jun 27, 2024 at 09:50:50PM +0100, Daniel Golle wrote:
> > Add notifier block to notify other subsystems about the addition or
> > removal of block devices.
> 
> Notification for what?  I really hate the concept of random modular
> code being able to hook into device discovery / partition scanning.

Adding a dedicated notification interface (instead of using block
internals in the nvmem driver) has been requested in a previous review
by Bart Van Assche:

https://patchwork.kernel.org/comment/25771998/

Quote from that previous review comment:
>>> Why to add this functionality to the block layer instead of somewhere
>>> in the drivers/ directory?
>> 
>> Simply because we need notifications about appearing and disappearing
>> block devices, or a way to iterate over all block devices in a system.
>> For both there isn't currently any other interface than using a
>> class_interface for that, and that requires access to &block_class
>> which is considered a block subsystem internal.
>
> That's an argument for adding an interface to the block layer that
> implements this functionality but not for adding this code in the block
> layer.
---

So that's what I did consequently. Using the notification interface
the NVMEM driver can live in drivers/nvmem/ and doesn't need to be
using block internals.

> And not actually having a user for it is a complete no-go.
> 

The user will be the nvmem provider, you can see the code in earlier
versions of the patchset where I had included it:

https://patchwork.kernel.org/project/linux-block/patch/96554d6b4d9fa72f936c2c476eb0b023cdd60a64.1717031992.git.daniel@makrotopia.org/

Being another subsystem I thought it'd be better to deal with the
block related things first, and once that has been sorted out I will
move on to add the NVMEM driver and make the necessary changes for
using it on eMMC.


Thank you for taking a look at this. Let me know if anything else
is not clear or needs to be changed.


Cheers


Daniel