Date: Mon, 4 Dec 2000 12:43:12 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: Matt Dillon <dillon@earth.backplane.com> Cc: Peter Wemm <peter@netplex.com.au>, "Kenneth D. Merry" <ken@kdm.org>, arch@FreeBSD.ORG Subject: Re: zero copy code review Message-ID: <14891.55103.81970.494533@grasshopper.cs.duke.edu> In-Reply-To: <200012040406.eB446jk70007@earth.backplane.com> References: <20001129231653.A1503@panzer.kdm.org> <200012040308.eB438tD52326@mobile.wemm.org> <14891.4047.626648.658103@grasshopper.cs.duke.edu> <200012040406.eB446jk70007@earth.backplane.com>
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Matt Dillon writes: > > :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 > That's a good point that I hadn't thought about. All the more reason to make the send-side code a socket option so the process has to take careful aim before blowing off its foot. Drew To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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