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=-6.6 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 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 1CE97C83000 for ; Tue, 28 Apr 2020 14:24:24 +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 D6D90206D7 for ; Tue, 28 Apr 2020 14:24:23 +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="UdamLnl0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D6D90206D7 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]:60562 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jTR9q-0006gD-W9 for qemu-devel@archiver.kernel.org; Tue, 28 Apr 2020 10:24:23 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43836) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jTR8U-0005AU-B3 for qemu-devel@nongnu.org; Tue, 28 Apr 2020 10:23:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.90_1) (envelope-from ) id 1jTR6l-0003Lz-P9 for qemu-devel@nongnu.org; Tue, 28 Apr 2020 10:22:57 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:53070 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jTR6l-0003Ky-9U for qemu-devel@nongnu.org; Tue, 28 Apr 2020 10:21:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588083669; 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=vXsfaqbKzbmyGzjd0hH35dirKJa0G/EnTg+YaT6oY1c=; b=UdamLnl0VaepkE+EO9cSt9Vv8LkgS0txUTFf9eNDIUTDwta+QOWBgxbUffQZuoUU3d/M4I PCRHSoiRbtz9EaXuGk3c+iRKYzJSaXKr29wpBgcG0k5RbEhpEUesBXf5zYz8MQKWpuM17g gr4oSHwx92kbA8ekMVtNzySP3P+HZJs= 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-170-M7iZ_cMeOA-yEmvPODHu3A-1; Tue, 28 Apr 2020 10:21:07 -0400 X-MC-Unique: M7iZ_cMeOA-yEmvPODHu3A-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5D69C462; Tue, 28 Apr 2020 14:21:06 +0000 (UTC) Received: from linux.fritz.box (ovpn-114-37.ams2.redhat.com [10.36.114.37]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 703B2272A7; Tue, 28 Apr 2020 14:21:05 +0000 (UTC) Date: Tue, 28 Apr 2020 16:21:04 +0200 From: Kevin Wolf To: Max Reitz Subject: Re: [PATCH 1/4] block: Add bdrv_make_empty() Message-ID: <20200428142104.GI5789@linux.fritz.box> References: <20200428132629.796753-1-mreitz@redhat.com> <20200428132629.796753-2-mreitz@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200428132629.796753-2-mreitz@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=kwolf@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/28 02:16:38 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] 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: qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 28.04.2020 um 15:26 hat Max Reitz geschrieben: > Right now, all users of bdrv_make_empty() call the BlockDriver method > directly. That is not only bad style, it is also wrong, unless the > caller has a BdrvChild with a WRITE permission. >=20 > Introduce bdrv_make_empty() that verifies that it does. >=20 > Signed-off-by: Max Reitz > --- > include/block/block.h | 1 + > block.c | 23 +++++++++++++++++++++++ > 2 files changed, 24 insertions(+) >=20 > diff --git a/include/block/block.h b/include/block/block.h > index b05995fe9c..d947fb4080 100644 > --- a/include/block/block.h > +++ b/include/block/block.h > @@ -351,6 +351,7 @@ BlockMeasureInfo *bdrv_measure(BlockDriver *drv, Qemu= Opts *opts, > void bdrv_get_geometry(BlockDriverState *bs, uint64_t *nb_sectors_ptr); > void bdrv_refresh_limits(BlockDriverState *bs, Error **errp); > int bdrv_commit(BlockDriverState *bs); > +int bdrv_make_empty(BdrvChild *c, Error **errp); > int bdrv_change_backing_file(BlockDriverState *bs, > const char *backing_file, const char *backing_fmt); > void bdrv_register(BlockDriver *bdrv); > diff --git a/block.c b/block.c > index 2e3905c99e..b0d5b98617 100644 > --- a/block.c > +++ b/block.c > @@ -6791,3 +6791,26 @@ void bdrv_del_child(BlockDriverState *parent_bs, B= drvChild *child, Error **errp) > =20 > parent_bs->drv->bdrv_del_child(parent_bs, child, errp); > } > + > +int bdrv_make_empty(BdrvChild *c, Error **errp) > +{ > + BlockDriver *drv =3D c->bs->drv; > + int ret; > + > + assert(c->perm & BLK_PERM_WRITE); If I understand correctly, bdrv_make_empty() is called to drop an overlay whose content is identical to what it would read from its backing file (in particular after a commit operation). This means that the caller promises that the visible content doesn't change. So should we check BLK_PERM_WRITE_UNCHANGED instead? Kevin