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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 63567FA3740 for ; Thu, 27 Oct 2022 19:13:33 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oo7gI-0001gG-3M; Thu, 27 Oct 2022 14:32:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oo7gE-0001QH-12 for qemu-devel@nongnu.org; Thu, 27 Oct 2022 14:32:38 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oo7g5-0002Qa-OV for qemu-devel@nongnu.org; Thu, 27 Oct 2022 14:32:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1666895548; 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=RnasrWm+CjyQZbUSmyF/kRm6yi1YGMwAsbxz3p/AmLI=; b=g9zgca6mSvVuwCh0mgDCbvUT9CIksrqyyurKwbnApDAfba79iU3lYuS85D5Hlu23/wggXo vBCUccBd/2KqJ9QENbiF5Kmaw1CXSRCIgFE1QyoYKFpPriO1sHvvTtnGT4eX279hej4A6G 0KeIRm9zHJh92yP9z1kYVdTP1O1a4bM= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-501-t8zIDIg7PBuaB-3S-V0KUg-1; Thu, 27 Oct 2022 14:32:25 -0400 X-MC-Unique: t8zIDIg7PBuaB-3S-V0KUg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E18453C0F66E; Thu, 27 Oct 2022 18:32:24 +0000 (UTC) Received: from merkur.fritz.box (unknown [10.39.194.12]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2D6FC1121320; Thu, 27 Oct 2022 18:32:24 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org Subject: [PULL 14/58] block: document connection between child roles and bs->backing/bs->file Date: Thu, 27 Oct 2022 20:31:02 +0200 Message-Id: <20221027183146.463129-15-kwolf@redhat.com> In-Reply-To: <20221027183146.463129-1-kwolf@redhat.com> References: <20221027183146.463129-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.515, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, T_SPF_TEMPERROR=0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Qemu-devel" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Vladimir Sementsov-Ogievskiy Make the informal rules formal. In further commit we'll add corresponding assertions. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Message-Id: <20220726201134.924743-8-vsementsov@yandex-team.ru> Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf --- include/block/block-common.h | 39 ++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/include/block/block-common.h b/include/block/block-common.h index fdb7306e78..fda67a7c38 100644 --- a/include/block/block-common.h +++ b/include/block/block-common.h @@ -313,6 +313,45 @@ enum { * * At least one of DATA, METADATA, FILTERED, or COW must be set for * every child. + * + * + * = Connection with bs->children, bs->file and bs->backing fields = + * + * 1. Filters + * + * Filter drivers have drv->is_filter = true. + * + * Filter node has exactly one FILTERED|PRIMARY child, and may have other + * children which must not have these bits (one example is the + * copy-before-write filter, which also has its target DATA child). + * + * Filter nodes never have COW children. + * + * For most filters, the filtered child is linked in bs->file, bs->backing is + * NULL. For some filters (as an exception), it is the other way around; those + * drivers will have drv->filtered_child_is_backing set to true (see that + * field’s documentation for what drivers this concerns) + * + * 2. "raw" driver (block/raw-format.c) + * + * Formally it's not a filter (drv->is_filter = false) + * + * bs->backing is always NULL + * + * Only has one child, linked in bs->file. Its role is either FILTERED|PRIMARY + * (like filter) or DATA|PRIMARY depending on options. + * + * 3. Other drivers + * + * Don't have any FILTERED children. + * + * May have at most one COW child. In this case it's linked in bs->backing. + * Otherwise bs->backing is NULL. COW child is never PRIMARY. + * + * May have at most one PRIMARY child. In this case it's linked in bs->file. + * Otherwise bs->file is NULL. + * + * May also have some other children that don't have the PRIMARY or COW bit set. */ enum BdrvChildRoleBits { /* -- 2.37.3