Re: [RFC] block layer support for DMA IOMMU bypass mode II

From: David S. Miller (
Date: Tue Jul 01 2003 - 19:21:36 EST

   From: Andi Kleen <>
   Date: Wed, 2 Jul 2003 02:22:44 +0200

   On Tue, 01 Jul 2003 17:03:23 -0700 (PDT)
   "David S. Miller" <> wrote:
> What do you mean? You map only one 4K chunk, and this is used
> for all the sub-1K mappings.
   How should this work when the 1K mappings are spread all over memory?
   Maybe I'm missing something but from James description it sounds like the
   block layer assumes that it can pass in a sglist with arbitary elements
   and get it back remapped to continuous DMA addresses.
It assumes it can pass in an sglist with arbitrary "virtually
contiguous" elements and get back a continuous DMA address.

The BIO_VMERGE_BOUNDRY defines the IOMMU page size and therefore
what "virtually contiguous" means.
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