linuxkpi: Add refcount_dec_and_test

[manu]

Summary

In Linux this takes a refcount_t argument but in linuxkpi struct kref
uses an atomic_t for the refcount and code in drm directly uses this
function with a kref so use an atomic_t here.

Sponsored by: Beckhoff Automation GmbH & Co. KG

[bz]

sys/compat/linuxkpi/common/include/linux/refcount.h

85

This may be a silly question, but why don't we fix kref instead to use refcount (now that it exists thanks to you)? Then this shouldn't be a problem here.

[manu]

sys/compat/linuxkpi/common/include/linux/refcount.h

85

TBH I haven't tested if this open a big can of worms or not ...

[bz]

sys/compat/linuxkpi/common/include/linux/refcount.h

85

I'll be happy to get this in and defer the answer to the worms for later maybe with an XXX should kref use refcount_t? next to it as well?

[manu]

sys/compat/linuxkpi/common/include/linux/refcount.h

85

Yeah I'll add something in linux/kref.h too.