Linux Zero Copy

From: Nagendra Singh Tomar (
Date: Wed Aug 13 2003 - 02:11:17 EST

Code walkthru of Linux 2.4.18 kernel reveals that we do copy from user
space for both linear and nonlinear skbuffs. What is this zerocopy thing
then ? If we are copying to different fragments of a non-linear skbuff
from user space, we can as well copy to a linear skbuff, to which the
headers can be prepended/appended by the protocol stack below.
I understand that a perfect zero-copy, wherein the user pages are
themselves DMA'ed by the NIC is very clumsy in UNIX (page flipping etc).
Am I missing something ??


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