How does the buffer get there in the first place? :-)
Yes, the zerocopy stuff is capable of doing this. But the block
I/O layer is not, neither is any other subsystem to my knowledge.
Certainly, when this changes, we can make the interfaces adapt to
Because of this, for example, the sbus IOMMU stuff on sparc32 still
uses HIGHMEM exactly because of this pointer limitation. In fact,
any machine using >4GB of memory currently cannot be supported without
highmem enabled, which is going to enable bounce buffering in the block
I/O layer, etc.
David S. Miller
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