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,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 632B7C432C0 for ; Mon, 25 Nov 2019 16:03:06 +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 310D920679 for ; Mon, 25 Nov 2019 16:03:06 +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="C17KgT7W" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 310D920679 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]:45944 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iZGpM-0005lu-Vd for qemu-devel@archiver.kernel.org; Mon, 25 Nov 2019 11:03:05 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:36839) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iZGnF-0003tG-JH for qemu-devel@nongnu.org; Mon, 25 Nov 2019 11:00:59 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iZGnB-00073K-V5 for qemu-devel@nongnu.org; Mon, 25 Nov 2019 11:00:51 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:53688 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iZGn9-00072U-CT for qemu-devel@nongnu.org; Mon, 25 Nov 2019 11:00:47 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574697646; 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=dGholLbexEcT6EajvtJ1ypQrkNDCDFhJDf3eUkuzUNM=; b=C17KgT7Wq2UTGsAMd71I8JeOE6s40JQiT+7y/08jpcBzvfw2Tfc2SMzs6vI5Ma7N8Dfp95 5UueogYATRQEFXT8TTXXEalOE3aprW38fBvrt5DW8is8ZG7Snd+JSJA/3MLOUPPTZ651ZE Ex8VGZ9zs7G3vRYoFcseqH+IgBtv4hc= 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-354-HWFy1os-P7C9Z0Pw_5RYtw-1; Mon, 25 Nov 2019 11:00:42 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9A7D0800594; Mon, 25 Nov 2019 16:00:41 +0000 (UTC) Received: from linux.fritz.box (unknown [10.36.118.9]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 465E35D9CD; Mon, 25 Nov 2019 16:00:39 +0000 (UTC) Date: Mon, 25 Nov 2019 17:00:37 +0100 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH 1/4] block/io: fix bdrv_co_block_status_above Message-ID: <20191125160037.GD4638@linux.fritz.box> References: <20191116163410.12129-1-vsementsov@virtuozzo.com> <20191116163410.12129-2-vsementsov@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <20191116163410.12129-2-vsementsov@virtuozzo.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-MC-Unique: HWFy1os-P7C9Z0Pw_5RYtw-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: 205.139.110.120 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, qemu-block@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com, stefanha@redhat.com, den@openvz.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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: >=20 > 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. 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. I honestly don't understand this one. Can you rephrase/explain in more detail what you mean by "stop inside [the] requested region"? > Fix these things, making logic about short backing files clearer. >=20 > 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. >=20 > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > block/io.c | 41 ++++++++++++++++++++++++++++---------- > tests/qemu-iotests/154.out | 4 ++-- > 2 files changed, 32 insertions(+), 13 deletions(-) >=20 > 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_abov= e(BlockDriverState *bs, > ret =3D bdrv_co_block_status(p, want_zero, offset, bytes, pnum, = 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, pro= duced > + * because current level is short. We should consider it as > + * allocated. "the selected region" "the current level" > + * TODO: Should we report p as file here? I think that would make sense. > */ > + assert(ret & BDRV_BLOCK_EOF); Can this assertion be moved above the if (first)? > *pnum =3D bytes; > + return BDRV_BLOCK_ZERO | BDRV_BLOCK_ALLOCATED; > } > - if (ret & (BDRV_BLOCK_ZERO | BDRV_BLOCK_DATA)) { > - break; > + if (ret & BDRV_BLOCK_ALLOCATED) { > + /* We've found the node and the status, we must return. */ > + > + if (ret & BDRV_BLOCK_ZERO && ret & BDRV_BLOCK_EOF && !first)= { > + /* > + * This level also responsible for reads after EOF insid= e > + * unallocated region in previous level. "is also responsible" "the unallocated region in the previous level" > + */ > + *pnum =3D bytes; > + } > + > + return ret; > } > - /* [offset, pnum] unallocated on this layer, which could be only > - * the first part of [offset, bytes]. */ Any reason for deleting this comment? I think it's still valid. > - bytes =3D MIN(bytes, *pnum); > + > + /* Proceed to backing */ > + assert(*pnum <=3D bytes); > + bytes =3D *pnum; > first =3D false; > } > + > return ret; > } Kevin