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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 7674CC432C0 for ; Tue, 26 Nov 2019 14:23:08 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 45FB3206BF for ; Tue, 26 Nov 2019 14:23:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="JpkFWJSg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 45FB3206BF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:55806 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iZbkB-00065E-BL for qemu-devel@archiver.kernel.org; Tue, 26 Nov 2019 09:23:07 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48663) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iZbhx-0004ki-At for qemu-devel@nongnu.org; Tue, 26 Nov 2019 09:20:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iZbhw-0001cC-5S for qemu-devel@nongnu.org; Tue, 26 Nov 2019 09:20:49 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:49728 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iZbhw-0001bu-1L for qemu-devel@nongnu.org; Tue, 26 Nov 2019 09:20:48 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574778047; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PyUVgxomDK1RSNDqnJdK15zFsxxzTnnQmFqskzxkhcM=; b=JpkFWJSgaAe5izjhWGxpjSF4KkbyrWAwJ8hLAd6+VQ1Xz4wi4Y6y0JuTVMVlZoCTM5A3ag mQdT9SpvPCjupAgOQDW+jUpkM4AHDF2WCNseJThj4Llv0YHxM1DI9o9R/dc68CCcHUH/EG q+UmD+jYdXSndeAeeb1Vyz9JULuwAdU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-262-mEvjoJXCOcaTjSbPswmN5w-1; Tue, 26 Nov 2019 09:20:46 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D5C46100E36F; Tue, 26 Nov 2019 14:20:44 +0000 (UTC) Received: from linux.fritz.box (ovpn-117-171.ams2.redhat.com [10.36.117.171]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 681D25C219; Tue, 26 Nov 2019 14:20:38 +0000 (UTC) Date: Tue, 26 Nov 2019 15:20:36 +0100 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH 1/4] block/io: fix bdrv_co_block_status_above Message-ID: <20191126142036.GA5889@linux.fritz.box> References: <20191116163410.12129-1-vsementsov@virtuozzo.com> <20191116163410.12129-2-vsementsov@virtuozzo.com> <20191125160037.GD4638@linux.fritz.box> <91f61957-33ec-ea91-d0c4-f555199c4d69@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <91f61957-33ec-ea91-d0c4-f555199c4d69@virtuozzo.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: mEvjoJXCOcaTjSbPswmN5w-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "fam@euphon.net" , Denis Lunev , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" , "mreitz@redhat.com" , "stefanha@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 26.11.2019 um 08:26 hat Vladimir Sementsov-Ogievskiy geschrieben: > 25.11.2019 19:00, Kevin Wolf wrote: > > Am 16.11.2019 um 17:34 hat Vladimir Sementsov-Ogievskiy geschrieben: > >> bdrv_co_block_status_above has several problems with handling short > >> backing files: > >> > >> 1. With want_zeros=3Dtrue, it may return ret with BDRV_BLOCK_ZERO but > >> without BDRV_BLOCK_ALLOCATED flag, when actually short backing file > >> which produces these after-EOF zeros is inside requested backing > >> sequesnce. > >=20 > > s/sequesnce/sequence/ > >=20 > >> > >> 2. With want_zeros=3Dfalse, it will just stop inside requested region,= if > >> we have unallocated region in top node when underlying backing is > >> short. > >=20 > > I honestly don't understand this one. Can you rephrase/explain in more > > detail what you mean by "stop inside [the] requested region"? >=20 > Hmm, yes, bad description. I mean, it may return pnum=3D0 prior to actual= EOF, > because of EOF of short backing file. Ah, yes, that's true. Definitely mention pnum=3D0 in the comment, this explanation is much clearer. > >> Fix these things, making logic about short backing files clearer. > >> > >> Note that 154 output changed, because now bdrv_block_status_above don'= t > >> merge unallocated zeros with zeros after EOF (which are actually > >> "allocated" in POV of read from backing-chain top) and is_zero() just > >> don't understand that the whole head or tail is zero. We may update > >> is_zero to call bdrv_block_status_above several times, or add flag to > >> bdrv_block_status_above that we are not interested in ALLOCATED flag, > >> so ranges with different ALLOCATED status may be merged, but actually, > >> it seems that we'd better don't care about this corner case. > >> > >> Signed-off-by: Vladimir Sementsov-Ogievskiy > >> --- > >> block/io.c | 41 ++++++++++++++++++++++++++++--------= -- > >> tests/qemu-iotests/154.out | 4 ++-- > >> 2 files changed, 32 insertions(+), 13 deletions(-) > >> > >> diff --git a/block/io.c b/block/io.c > >> index f75777f5ea..4d7fa99bd2 100644 > >> --- a/block/io.c > >> +++ b/block/io.c > >> @@ -2434,25 +2434,44 @@ static int coroutine_fn bdrv_co_block_status_a= bove(BlockDriverState *bs, > >> ret =3D bdrv_co_block_status(p, want_zero, offset, bytes, pn= um, map, > >> file); > >> if (ret < 0) { > >> - break; > >> + return ret; > >> } > >> - if (ret & BDRV_BLOCK_ZERO && ret & BDRV_BLOCK_EOF && !first) = { > >> + if (*pnum =3D=3D 0) { > >> + if (first) { > >> + return ret; > >> + } > >> + > >> /* > >> - * Reading beyond the end of the file continues to read > >> - * zeroes, but we can only widen the result to the > >> - * unallocated length we learned from an earlier > >> - * iteration. > >> + * Reads from bs for selected region will return zeroes, = produced > >> + * because current level is short. We should consider it = as > >> + * allocated. > >=20 > > "the selected region" > > "the current level" > >=20 > >> + * TODO: Should we report p as file here? > >=20 > > I think that would make sense. > >=20 > >> */ > >> + assert(ret & BDRV_BLOCK_EOF); > >=20 > > Can this assertion be moved above the if (first)? >=20 > it may correspond to requested bytes=3D=3D0.. But we can check it separat= ely > before for loop and move this assertion. Ah, right. Don't bother then, it's fine either way. Kevin