From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9BA1DC4332F for ; Thu, 10 Nov 2022 15:03:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230372AbiKJPDs (ORCPT ); Thu, 10 Nov 2022 10:03:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229869AbiKJPDo (ORCPT ); Thu, 10 Nov 2022 10:03:44 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B743718B1C; Thu, 10 Nov 2022 07:03:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=dyByMJ1FnM8pS9wy50nx7QIU4ShnY0C2LEYs5nLdq7s=; b=BZ59WACHJvZgfqFRB11gUk1yT1 brXqYTm1gv1aZxTv8tk2GAw2D+qpM99gV17oc69z0YTx6XC3caEX7i0sW7hIJXiCULSh5GMSgPDMe Ayqde6NPh7Cm5mazI4Gkmtd/s6UIg8p4x00orrdTwetPvHsBWREXjl0weKX53b3pDBMWeskm4idE7 +IMqt/j9BV4KeytyL2eH4DoqZgEs5lDw5BKe8dlgSG8lfOlfOvRGnm/ecdmuCZ913y68IGrk3zBpO OzCgbyl+7DRlX2T8WzHF0abvztYBzhOcVcZh87PWfTLSuuLeZBDFqthO2I8LtrbuR7kbBp0TsopOl 8zIn8MzA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1ot953-00C9kk-GP; Thu, 10 Nov 2022 15:03:01 +0000 Date: Thu, 10 Nov 2022 15:03:01 +0000 From: Matthew Wilcox To: Daniel Golle Cc: Jens Axboe , Miquel Raynal , Richard Weinberger , Vignesh Raghavendra , Davidlohr Bueso , "Martin K. Petersen" , Chaitanya Kulkarni , Ming Lei , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org, linux-efi@vger.kernel.org Subject: Re: [PATCH v4 2/5] block: add partition parser for U-Boot uImage.FIT Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 10, 2022 at 01:52:43AM +0000, Daniel Golle wrote: > On Wed, Nov 09, 2022 at 05:21:01PM +0000, Matthew Wilcox wrote: > > On Wed, Nov 09, 2022 at 02:36:11PM +0000, Daniel Golle wrote: > > > On Wed, Nov 09, 2022 at 01:58:29PM +0000, Matthew Wilcox wrote: > > > > ... actually, why can't you call read_part_sector() and avoid all of > > > > this? > > > > > > I've tried that before and the problem is that read_part_sector() > > > returns a pointer to one sector (typically 512 bytes) of data. > > > And this pointer should not be accesses beyond sector boundaries, > > > right? You'd have to call read_part_sector() again for the next > > > sector. > > > > > > The FIT structure, however, usually exceeds the size of one sector, > > > and having a continous memory area covering the structure as a whole > > > is crucial for libfdt to do its job. > > > > > > I could, of course, use read_part_sector() to copy all sectors > > > covering the FIT structure into a buffer, but that seemed strange > > > given that read_part_sector() actually used read_mapping_page() > > > (and now uses read_mapping_folio()) internally and then returns a > > > pointer to the offset within the page/folio. So why not read it in one > > > piece in first place instead of having it first split up to sectors > > > by read_part_sector() just to then having to reassemble it into a > > > continous buffer again. > > > > Are you guaranteed that it's "sufficiently" aligned on storage so > > that it fits entirely within a single page? If not, you'll have > > to copy it, vmap it, or fix libfdt to handle a segmented buffer. > > Yes, for the uImage.FIT to be usable for the partition parser it has > to be page-aligned. > > There is a check which makes sure that this is the case: > > + /* uImage.FIT should be aligned to page boundaries */ > > + if (fit_start_sector % (1 << (PAGE_SHIFT - SECTOR_SHIFT))) > > + return 0; > > In case of mtdblock or ubiblock devices, the image always starts at > offset 0, so this is never a problem. > In case of the image being stored in a GPT partition, one has to make > sure that the start sector of the partition is page aligned, otherwise > the above check will fail and the partition parser will bail out. OK. Then I think open coding it is the right idea, just with all the cruft removed ;-) I looked at extracting parts of read_part_sector() into read_part_page(), but it ended up being a two line function that wasn't terribly useful.