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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3AADBC07E95 for ; Tue, 20 Jul 2021 21:21:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 185CC61003 for ; Tue, 20 Jul 2021 21:21:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233113AbhGTUjx (ORCPT ); Tue, 20 Jul 2021 16:39:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50736 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232037AbhGTUiq (ORCPT ); Tue, 20 Jul 2021 16:38:46 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 056D8C061762; Tue, 20 Jul 2021 14:19:23 -0700 (PDT) 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=jH0gd7w7NQ82Sj3yTDMI2muMiPUSaHJ1LlIGDUYck8Q=; b=vtbK6X1QUhUbVCiHXfWP/ExRhw KNQBUSvy3uO+ot2vISeYwiVvAmHqXuITG+dcTbAodKGPGppApGDarmD7ySu8lNjM1ROP/urIEfmYA 8FLE8SulGrQSPoVDPtZkYbqvceKsWuPKzVNyT2zPK1+0UnEjPpe6BEGDkM+lOM+lL3uAin9Hr552g VJtJIg/rquTd/yhHBDg8q1Zl5UEj+GcK88pFPQvbvCVtCvEaiSfdKPEpiEcCpviuzAoqmgrhz0FGp 0uXG+65cOTsV05ZbWzdH7DtYSGYLClzsXM0fBx4Wtn4fjWU1CiJg5Lmnur9R61Eky9YLHdE5X+/Ju 2mwIgtDA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1m5x8g-008WDw-B4; Tue, 20 Jul 2021 21:18:57 +0000 Date: Tue, 20 Jul 2021 22:18:54 +0100 From: Matthew Wilcox To: "Darrick J. Wong" Cc: Gao Xiang , linux-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org, LKML , Christoph Hellwig , Andreas Gruenbacher Subject: Re: [PATCH v4] iomap: support tail packing inline read Message-ID: References: <20210720133554.44058-1-hsiangkao@linux.alibaba.com> <20210720204224.GK23236@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210720204224.GK23236@magnolia> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 20, 2021 at 01:42:24PM -0700, Darrick J. Wong wrote: > > - BUG_ON(page_has_private(page)); > > - BUG_ON(page->index); > > - BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data)); > > + /* inline source data must be inside a single page */ > > + BUG_ON(iomap->length > PAGE_SIZE - offset_in_page(iomap->inline_data)); > > Can we reduce the strength of these checks to a warning and an -EIO > return? I'm not entirely sure that we need this check, tbh. > > + /* handle tail-packing blocks cross the current page into the next */ > > + size = min_t(unsigned int, iomap->length + pos - iomap->offset, > > + PAGE_SIZE - poff); > > > > addr = kmap_atomic(page); > > - memcpy(addr, iomap->inline_data, size); > > - memset(addr + size, 0, PAGE_SIZE - size); > > + memcpy(addr + poff, iomap->inline_data - iomap->offset + pos, size); > > + memset(addr + poff + size, 0, PAGE_SIZE - poff - size); > > Hmm, so I guess the point of this is to support reading data from a > tail-packing block, where each file gets some arbitrary byte range > within the tp-block, and the range isn't aligned to an fs block? Hence > you have to use the inline data code to read the relevant bytes and copy > them into the pagecache? I think there are two distinct cases for IOMAP_INLINE. One is where the tail of the file is literally embedded into the inode. Like ext4 fast symbolic links. Taking the ext4 i_blocks layout as an example, you could have a 4kB block stored in i_block[0] and then store bytes 4096-4151 in i_block[1-14] (although reading https://www.kernel.org/doc/html/latest/filesystems/ext4/dynamic.html makes me think that ext4 only supports storing 0-59 in the i_blocks; it doesn't support 0-4095 in i_block[0] and then 4096-4151 in i_blocks) The other is what I think erofs is doing where, for example, you'd specify in i_block[1] the block which contains the tail and then in i_block[2] what offset of the block the tail starts at.