Re: [PATCH 5/5] firmware: add DECLARE_FW_CUSTOM_FALLBACK() annotation

[Luis R. Rodriguez]

On Fri, Dec 16, 2016 at 05:10:18PM +0100, Luis R. Rodriguez wrote:
> Ah, well Milo Kim replied and described that the custom fallback is used as to
> help load LED effect manually, and suggested a sysfs interface is more ideal [0]. I
> agree however its also may be too late, and it depends how wide spread this "userspace"
> that relies on this is, we just can't break it. Granted the custom fallback
> mechanism was broken since v4.0 (see the fix "firmware: fix usermode helper
> fallback loading") so one may argue no one seems to care...
> 
> So this is a judgement call, and the declaration is to point to documentation
> to white list uses, as terrible as this one is userspace exists for it. but
> more importantly to also help the SmPL grammar report to avoid reporting
> already vetted cases. The alarm / cases for the 2 drivers has been issueed,
> moving forward the lack of declaration with the custom fallback should trigger
> a rant through 0-day so we don't run into the same stupid situation.
> 
> [0] https://marc.info/?l=linux-kernel&m=148168024112445

Milo if sysfs is used can't the old userspace be mapped to use the new 
sysfs interface through a wrapper of some sort ? What exactly would be
needed to ensure old userspace will not break? Why has no one cried
after the v4.0 custom fallback mechanism breaking ? How wide spread is
this custom userspace ?

  Luis