Re: pte_pagenr/MAP_NR deleted in pre6

[Kanoj Sarcar <kanoj@google.engr.sgi.com>]

> 
>    Whatever you do, you either have to introduce paddr_t (which to me
>    seems more intuitive) or page_to_pfn. We can argue one way or
>    another, but paddr_t might give you type checking for free too ...
> 
> My only two gripes about paddr_t is that long long is not only
> expensive but has been also known to be buggy on 32-bit platforms.

Yeah, yeah, I know ... (I didn't know about the buggy bit though).
OTOH, paddr_t is such an intuitive concept (and without any disadvantages
on any platform other than i386-PAE), its unfortunate if it
gets shot down just because of this ...

> 
> The next gripe is that it will make many clueless driver
> etc. developers (who don't read documentation even, but write a large
> portion of the vendor Linux drivers :-) will try to do things
> like "void *p = (void *) (PAGE_OFFSET + x->paddr);" and expect
> this to work, or maybe they'll even pass it to virt_to_bus or similar.

Wait! You are saying you have a scheme that will prevent writers 
from writing buggy code that happens to work only on 32Mb i386 ...
Go ahead, I am all ears :-)

Basically, with all the pci-dma and sct's alternate page_to_pfn
suggestion interfaces, you still can not claim that people will 
not do 

	void *p = (void *) (PAGE_OFFSET + page_to_pfn(p) << PAGE_SHIFT)

and check that code in because it works on their 1Gb i386 box. No?

Kanoj
 
> If people don't think these two things will be an issue, fine with
> me. :-)
> 
> Which reminds me, we need to schedule a field day early 2.5.x where
> virt_to_bus and bus_to_virt are exterminated, this is the only way we
> can move to drivers using page+offset correctly, forcing them through
> interface such as the pci_dma API instead.
> 
> Later,
> David S. Miller
> davem@redhat.com
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