Nick Piggin wrote:
Nonlinear mappings are (AFAIKS) simply a virtual memory concept that
encodes the virtual address -> file offset differently from linear
mappings.
I can't see why the filesystem/pagecache code should need to know anything
about it, except for the fact that the ->nopage handler didn't quite pass
down enough information (ie. pgoff). But it is more logical to pass pgoff
rather than have the ->nopage function calculate it itself anyway. And
having the nopage handler install the pte itself is sort of nasty.
This patch introduces a new fault handler that replaces ->nopage and ->populate
and (hopefully) ->page_mkwrite. Most of the old mechanism is still in place
so there is a lot of duplication and nice cleanups that can be removed if
everyone switches over.
The rationale for doing this in the first place is that nonlinear mappings
are subject to the pagefault vs invalidate/truncate race too, and it seemed
stupid to duplicate the synchronisation logic rather than just consolidate
the two.
Comments?
That's pretty nice.
Back when I was writing [the now slated for death]
sound/oss/via82xxx_audio.c driver, Linus suggested that I implement
->nopage() for accessing the mmap'able DMA'd audio buffers, rather than
using remap_pfn_range(). It worked out very nicely, because it allowed
the sound driver to retrieve $N pages for the mmap'able buffer (passed
as an s/g list to the hardware) rather than requiring a single humongous
buffer returned by pci_alloc_consistent().
And although probably not your primary motivation, your change does IMO
improve this area of the kernel.
Jeff
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