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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A31E7C433F5 for ; Tue, 9 Nov 2021 07:00:37 +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 55D6D61151 for ; Tue, 9 Nov 2021 07:00:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 55D6D61151 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:42364 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mkL7U-0000B8-9e for qemu-devel@archiver.kernel.org; Tue, 09 Nov 2021 02:00:36 -0500 Received: from eggs.gnu.org ([209.51.188.92]:58606) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mkKrk-0000y4-M5 for qemu-devel@nongnu.org; Tue, 09 Nov 2021 01:44:20 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:30606) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mkKrg-0007cl-So for qemu-devel@nongnu.org; Tue, 09 Nov 2021 01:44:20 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636440255; 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: in-reply-to:in-reply-to:references:references; bh=E0IYkj+cq2T2HDHh1iXRB9KmACnHrvBndKNfBpmjQsU=; b=Pv+cp5dqno9UigVkkbRRo3ckr1TZl6DfWjY0RpwpZzEtOLFx++rEtcGtbpZlTNMOpRQiJk C7VMiP7OMmnZlWH7Jr+jAcCxSvmhHbn0Xa2jBHlz+QLNgJ+bCSR2oo4cwsLEpQV7oXFJuE UDWUIwzobE3dXmzZqHyFibZmClEUKc8= 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-219-Ox9tzCSaN4GGa4QUjKnAeg-1; Tue, 09 Nov 2021 01:44:14 -0500 X-MC-Unique: Ox9tzCSaN4GGa4QUjKnAeg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0EF131006AA0; Tue, 9 Nov 2021 06:44:13 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-7.ams2.redhat.com [10.36.112.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CFDF25F4E9; Tue, 9 Nov 2021 06:44:12 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 1628F11380A7; Tue, 9 Nov 2021 07:44:11 +0100 (CET) From: Markus Armbruster To: qemu-devel@nongnu.org Subject: Re: Poking around bdrv_is_inserted() References: <87tuglg7ly.fsf@dusky.pond.sub.org> Date: Tue, 09 Nov 2021 07:44:11 +0100 In-Reply-To: <87tuglg7ly.fsf@dusky.pond.sub.org> (Markus Armbruster's message of "Tue, 09 Nov 2021 07:34:33 +0100") Message-ID: <8735o5g75w.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: , Cc: Kevin Wolf , Hanna Reitz , qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Screwed up qemu-devel@nongnu.org, sorry for the inconvenience. Markus Armbruster writes: > bdrv_is_inserted() returns false when: > > /** > * Return TRUE if the media is present > */ > bool bdrv_is_inserted(BlockDriverState *bs) > { > BlockDriver *drv = bs->drv; > BdrvChild *child; > > if (!drv) { > return false; > > 1. @bs has no driver (this is how we represent "no medium"). > > } > if (drv->bdrv_is_inserted) { > return drv->bdrv_is_inserted(bs); > > 2. Its driver's ->bdrv_is_inserted() returns false. This is how > passthrough block backends signal "host device has no medium". Right > now, the only user is "host_cdrom". > > } > QLIST_FOREACH(child, &bs->children, next) { > if (!bdrv_is_inserted(child->bs)) { > return false; > > 3. Any of its children has no medium. Common use looking through > filters, which have a single child. > > } > } > return true; > } > > Makes sense. > > Now look at the uses of QERR_DEVICE_HAS_NO_MEDIUM. > > * external_snapshot_prepare() in blockdev.c: > > if (!bdrv_is_inserted(state->old_bs)) { > error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, device); > goto out; > } > > where @device is the device name, i.e. BlockdevSnapshot member @node > or BlockdevSnapshotSync member @device. Uh-oh: the latter can be > null. If we can reach the error_setg() then, we crash on some > systems. > > * bdrv_snapshot_delete() and bdrv_snapshot_load_tmp() in > block/snaphot.c: > > if (!drv) { > error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, bdrv_get_device_name(bs)); > return -ENOMEDIUM; > } > > where @drv is bs->drv. > > Why do we check only for 1. here instead of calling > bdrv_is_inserted()?