Date: Fri, 2 Jan 2009 11:27:05 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.rg> To: Gerry Weaver <gerryw@compvia.com> Cc: freebsd-fs@freebsd.org Subject: Re: Headers files included by vnode.h Message-ID: <alpine.BSF.2.00.0901021124520.56000@fledge.watson.org> In-Reply-To: <20081223201626.caa483ad@mail01.compvia.com> References: <20081223201626.caa483ad@mail01.compvia.com>
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On Tue, 23 Dec 2008, Gerry Weaver wrote: > Perfect. Yes, I am building a kernel module. This is exactly what I was > looking for. I really appreciate your help. > > I am also trying to figure out a zero copy approach to kernel memory access > from user space. Would you happen to know which list I should post the > question to? Hi Gerry: It depends a bit what you want to accomplish with zero-copy. Are you just looking for a temporary mapping into kernel space for a user page, or a mapping of a kernel page into userspace? Is it only for use by privileged processes, or is this general-purpose? There are a number of concerns to think about, such as where the page comes from, whether leaked information that might also be present in the same page, if allocated from a general user of kernel pool, might be an issue, and how to tell when you're done with the page. If you just want a kernel facility to borrow a page from a user process temporarily, take a look at src/sys/net/bpf_zerocopy.c in 8.x, which borrows a set of user pages to use in-kernel for the duration of a BPF session. Robert N M Watson Computer Laboratory University of Cambridge
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