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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 5D5D1C388EB for ; Thu, 6 Feb 2020 15:11:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2B8D820838 for ; Thu, 6 Feb 2020 15:11:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="QLJk1DSS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727529AbgBFPL6 (ORCPT ); Thu, 6 Feb 2020 10:11:58 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:37532 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727509AbgBFPLn (ORCPT ); Thu, 6 Feb 2020 10:11:43 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=ZFk7IOgbesF7yVq11kopj6A6elmWy+W9AHpajAqV7CE=; b=QLJk1DSSipqWnEpF2DbSQ3LSPj SzI2RXW9pjb+WPUuPVsg9tLxNCvwnsiEkhlg4cfj96bfW79i0JFaG0UiZKgJSanPdh5lzvdiggLj2 CbXEfVq8q/44MIuKTHgslsjGXRqwtRak3ESd8W7ee8VjspSKtf8Qb4f2Bwvgr+sSEpRg1Eks/XFFO HTHQm7MyBwHpsqAiH4c2DgOn5bbGqjguu9YSP0eXMkDALYH2T5qabnAerjjeCnKRGbwUk2KCtmxOh PHZwmUFjYjRebG0K+8/TjL5q6ieqaaimzAFA6PmvbyyNZ1xKOe+kyYBYlmv1347sYreL7JbMDHgaL 9vuBYmmg==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1izibP-0006UI-3f; Thu, 06 Feb 2020 14:57:59 +0000 Date: Thu, 6 Feb 2020 06:57:59 -0800 From: Christoph Hellwig To: Johannes Thumshirn Cc: Christoph Hellwig , David Sterba , Nikolay Borisov , Josef Bacik , "linux-btrfs @ vger . kernel . org" Subject: Re: [PATCH v4 1/5] btrfs: use the page-cache for super block reading Message-ID: <20200206145759.GA24780@infradead.org> References: <20200205143831.13959-1-johannes.thumshirn@wdc.com> <20200205143831.13959-2-johannes.thumshirn@wdc.com> <20200205165319.GA6326@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Thu, Feb 06, 2020 at 08:17:20AM +0000, Johannes Thumshirn wrote: > >> + super = kmap(page); > >> if (btrfs_super_bytenr(super) != bytenr || > >> btrfs_super_magic(super) != BTRFS_MAGIC) { > >> - brelse(bh); > >> + kunmap(page); > >> + put_page(page); > >> return -EINVAL; > >> } > >> + kunmap(page); > > > > Also last time I wondered why we can't leave the page mapped for the > > caller and also return the virtual address? That would keep the > > callers a little cleaner. Note that you don't need to pass the > > struct page in that case as the unmap helper can use kmap_to_page (and > > I think a helper would be really nice for the unmap and put anyway). > > > > There's btrfs_release_disk_super() but David didn't like the use of it > in v2 of this series. But when using a 'struct btrfs_disk_super' instead > of a 'struct page' I think he could be ok. Also I just noticed don't even need the kmap/kunmap at all given that the block device mapping is never in highmem.