Date: Sun, 3 Dec 2000 20:06:45 -0800 (PST) From: Matt Dillon <dillon@earth.backplane.com> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: Peter Wemm <peter@netplex.com.au>, "Kenneth D. Merry" <ken@kdm.org>, arch@FreeBSD.ORG Subject: Re: zero copy code review Message-ID: <200012040406.eB446jk70007@earth.backplane.com> References: <20001129231653.A1503@panzer.kdm.org> <200012040308.eB438tD52326@mobile.wemm.org> <14891.4047.626648.658103@grasshopper.cs.duke.edu>
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:freed). We do not make anything COW for the kernel.
:
: > either, but I could have missed it.. What about drivers that DMA to pages
: > mapped into KVM without checking writability (and hence COW)?
:
:This is a good point. But I cannot think of any circumstance where a
:driver would be DMA'ing directly to a user owned page (with the
:exception of a vm fault, but this is impossible because the pages are
:resident prior to setting up the send and are wired for the duration
:of the send).
:
:Thanks for the input. I'm glad to see you and Matt looking at this!
:
:Drew
Careful. If you read() from a raw device most disk drivers WILL dma
directly to a user-owned page.
-Matt
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