Runtime check for PAE option on BSD 6+ i386

[John Baldwin]

On Tuesday, May 03, 2011 9:10:26 am Philip Soeberg wrote:
> Hi fellow FreeBSD hackers,
> 
> I've been using the following poor-man's approach in my driver init for 
> ages in an attempt at detecting PAE option on BSD 6 (or greater) i386 
> kernels, as I depend on dmabus(9) but provide a loadable kernel module only.
> 
>  >>>
>    if (sizeof(void*) == 4) {
>      if (((uint64_t)(cnt.v_page_count * cnt.v_page_size) / 1073741824) 
>  >= 4) {
>        printf("FreeBSD i386 detected with PAE option enabled. FreeBSD 
> PAE type\n");
>        printf("kernels does not support loadable modules which use DMA. 
> Please\n");
>        printf("reconfigure your kernel for non-PAE or switch to amd64 
> kernel.\n");
>        return EFAULT;
>      }
>    }
> <<<

Hmmm, even this isn't really accurate as some folks may choose to enable PAE
even with < 4GB to get PG_NX functionality.
 
> afaik there's a sysctl method of checking this per BSD7 (or is it 8?), 
> but what about BSD6? Any hints on how I can runtime detect the above?

Definitely a kern.features.pae sysctl in 7.  I don't see anything similar in 
6.  

-- 
John Baldwin