From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sj-iport-6.cisco.com (sj-iport-6.cisco.com [171.71.176.117]) by ozlabs.org (Postfix) with ESMTP id 2C05ADDE07 for ; Fri, 12 Jan 2007 06:55:00 +1100 (EST) To: Christoph Hellwig Subject: Re: [PATCH/RFC 2.6.21 2/5] ehca: ehca_uverbs.c: "proper" use of mmap References: <200701112008.15841.hnguyen@linux.vnet.ibm.com> <20070111194000.GE24623@infradead.org> From: Roland Dreier Date: Thu, 11 Jan 2007 11:54:58 -0800 In-Reply-To: <20070111194000.GE24623@infradead.org> (Christoph Hellwig's message of "Thu, 11 Jan 2007 19:40:00 +0000") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, openib-general@openib.org, openfabrics-ewg@openib.org, linuxppc-dev@ozlabs.org, raisch@de.ibm.com, Hoang-Nam Nguyen List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > > int ehca_mmap(struct ib_ucontext *context, struct vm_area_struct *vma) > > { > > Can you split this monster routine into individual functions for > each type of mmap please? With two helpers to get and verify the cq/qp > shared by the individual sub-variants, that would also help to get rid > of all those magic offsets. > > Actually, this routine directly comes from ib_device.mmap - Roland, > can you shed some light on what's going on here? Each userspace-accessible IB device gets a single device node like /dev/infiniband/uverbsX. Opening that gives userspace a "context". One of the things userspace can do with that fd is mmap() on it -- that was originally envisioned as a way to map a page of hardware registers directly in to the userspace process. It seems ehca needs to allocate lots of different things in the kernel via mmap(). What you're saying I guess is that ideally each of these would be mmap() on a different fd rather than using different offsets. It's a little awkward to open multiple device nodes to get multiple fds, since there's not a good way to attach them all to the same context. I guess we could create some hack to return more file handles, but I think that cure is worse than the disease of using magic offsets... Maybe longer term we need to look at a scheme like cell's spufs but I'm still not confident we have the RDMA interface quite ready to freeze at the system call level. - R.