How to replace set_fs(KERNEL_DS) for a kernel 5.10.x module driver version

[Jorge Fernandez Monteagudo]

>> Well, I can summarize as technological debt :( 
>> I have to maintain an old code and I've been succesful until now with
>> minimal changes... Is there no way to overcome this?
>
>There might be, again, do you have a pointer to your full source for the
>module?
>
Well, I don't know if I'm allowed to share the full source code... But, is it not enough with the minimal code I attached to grasp the problem?
With the original kernel modules I'll have problems with the read/write functions because they use the set_fs/get_fs functions too but I think it's not an option to rewrite the driver as a userspace library and maybe I should remain using a < 5.10.x kernel...

Thanks,
Jorge