Re: Seeking advice on "monkey patching" a driver

Greg KH
2021-07-02T04:31:46Z

On Thu, Jul 01, 2021 at 03:03:12PM -0500, Ian Pilcher wrote:
> On 7/1/21 12:59 PM, Greg KH wrote:
> > Oh that's horrible, please no, do not do that :)
>
> Indeed it is, but it works, and it meets my main objective, which is to
> allow the use of distribution kernel packages and modules.
>
> > How about a third option, the correct one:
> > - submit your code changes upstream and they get merged into the
> > main kernel tree and no monkeypatching is ever needed at all!
> >
> > Have you submitted your changes upstream to the existing drivers? What
> > is preventing that from happening today?
>
> There are a couple of reasons that I've never attempted to do this.
>
> * Scope of work - Currently, there is simply no mechanism to call an LED
> trigger from the ahci or libahci modules, presumably because this is
> something that really ought to be done by the hardware. So I would
> have to add some sort of generic framework to associate LED triggers
> with AHCI ports.
>
> I probably also don't really have the knowledge to do this. I am not
> familiar with locking, memory management, etc. in the kernel. Just
> because my "hack" works on a specific 2-core NAS doesn't mean that it
> won't cause all sorts of breakage on a higher-performance system with
> more parallelism.

Why are ahci devices somehow "special" here? Just add a trigger to the
ahci core for LEDs and all should "just work". We've done that for many
subsystems already.

> * (Probable) lack of upstream interest - As I mentioned, disk activity
> LEDs really ought to be handled by the hardware. I don't know of any
> other system that suffers from this particular limitation. So this
> is a very, very niche use case. (Most users of this hardware use the
> manufacturer's "firmware".)

Are you sure we don't already have LED triggers for disk activity? Have
you tried the ledtrig-disk.c driver? It says it works on ATA devices,
no reason it can't also work for other device types.

> I did ask about this on the linux-ide mailing list long ago when I
> first wrote the modules, but I don't think that I ever received a
> response, which reinforces my belief that upstream isn't likely to be
> receptive.
>
> I've invested significant time in kernel patches in the past, only to
> see them ultimately not be accepted, so I would need to know that
> upstream was truly interested in such a feature before I would consider
> making such a commitment.

That's not fair, there is no way anyone can promise anyone that their
patches will be accepted, _before_ anyone sees them. What would _you_
do if you were in the kernel maintainer's position and read something
like this?

good luck!

greg k-h