Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756249AbZFDHcY (ORCPT ); Thu, 4 Jun 2009 03:32:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752346AbZFDHcR (ORCPT ); Thu, 4 Jun 2009 03:32:17 -0400 Received: from brick.kernel.dk ([93.163.65.50]:60398 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751945AbZFDHcR (ORCPT ); Thu, 4 Jun 2009 03:32:17 -0400 Date: Thu, 4 Jun 2009 09:32:18 +0200 From: Jens Axboe To: Leon Woestenberg Cc: Steve Rottinger , linux-kernel@vger.kernel.org Subject: Re: splice methods in character device driver Message-ID: <20090604073218.GT11363@kernel.dk> References: <4A0838D1.5090102@pentek.com> <20090511192253.GH4694@kernel.dk> <4A0AFC62.3090002@pentek.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2141 Lines: 73 On Wed, Jun 03 2009, Leon Woestenberg wrote: > Hello all, > > On Wed, May 13, 2009 at 6:59 PM, Steve Rottinger wrote: > > is passing in the pages into splice_to_pipe. ?The pages are associated > > with a PCI BAR, not main memory. ?I'm wondering if this could be a problem? > > > Good question; my newbie answer would be the pages need to be mapped > in kernel space. That is what the ->map() hook is for. > I have a similar use case but with memory being DMA'd to host main > memory (instead of the data sitting in your PCI device) in a character > device driver. The driver is a complete rewrite from scratch from > what's currently sitting-butt-ugly in staging/altpcichdma.c > so-please-don't-look-there. > > I have already implemented zero-latency overlapping transfers in the > DMA engine (i.e. it never sits idle if async I/O is performed through > threads), now it would be really cool to add zero-copy. > > What is it my driver is expected to do? > > .splice_read: > > - Allocate a bunch of single pages > - Create a scatter-gather list > - "stuff the data pages in question into a struct page *pages[]." a la > "fs/splice.c:vmsplice_to_pipe()" > - Start the DMA from the device to the pages (i.e. the transfer) > - Return. > > .splice_write: > > - Create a scatter-gather list > > interrupt handler / DMA service routine: > - device book keeping > - wake_up_interruptible(transfer_queue) > > .confirm(): > > "then you need to provide a suitable ->confirm() hook that can wait on > this IO to complete if needed." > - wait_on_event_interruptibe(transfer_queue) > > .release(): > > - release the pages > > .steal(): > > unsure This is what allows zero copy throughout the pipe line. ->steal(), if sucesful, should pass ownership of that page to the caller. The previous owner must no longer modify it. > .map > > unsure See above :-) -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/