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DateThu, 18 May 2006 11:36:50 -0400
FromJeff Garzik <>
SubjectRe: support for sata7 Streaming Feature Set?
Tejun Heo wrote:
> One thing to think about before supporting streaming from/to harddisks
> from userland is how to make data flow efficiently from userland to
> kernel and back. But, no matter what, kernel <-> userland usually
> involves one data copy, so I don't think making sg similarly efficient
> would be too difficult (it might be already).

Actually, the kernel usually maps userland pages, eliminating the need
for a copy. write(2) may have copied data into that page originally,
but mmap(2) need not have.

Jeff


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