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 lists1p.gnu.org (lists1p.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 60025CC6B12 for ; Tue, 13 Oct 2026 19:15:36 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xGhxx-0006sK-My; Tue, 13 Oct 2026 15:15:13 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xGhxt-0006qt-17 for qemu-devel@nongnu.org; Tue, 13 Oct 2026 15:15:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xGhxq-0006uR-K3 for qemu-devel@nongnu.org; Tue, 13 Oct 2026 15:15:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1791918906; 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=6pQItpLNj9iHG8udG2WFaVAMclVzFKxcOVXOagydeUg=; b=CaloqABfIpsMYdRUxQLAkB0Nk3G0YF8LeTBUUoDGpttHhsOZ69T8/S2V0ZQK0Jmq9nyk+r dD/UL9frb38ePIXBw3Whn/m0aypxUX8RInOKpQo7lyHGHV+OlaoZdxUFv2WvYd5MGkJRHv WkoOgjRbgccFqowwip8ftFM73+MEcME= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-114-b4MJXhOvNeSmTQlrHQOJBg-1; Tue, 13 Oct 2026 19:15:01 +0000 X-MC-Unique: b4MJXhOvNeSmTQlrHQOJBg-1 X-Mimecast-MFC-AGG-ID: b4MJXhOvNeSmTQlrHQOJBg_1791918900 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DCBCD180A365; Tue, 13 Oct 2026 19:14:59 +0000 (UTC) Received: from redhat.com (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 194C23001D29; Tue, 13 Oct 2026 19:14:57 +0000 (UTC) Date: Tue, 13 Oct 2026 14:14:55 -0500 From: Eric Blake To: Ilya Leoshkevich Cc: Kevin Wolf , Hanna Reitz , qemu-block@nongnu.org, qemu-devel@nongnu.org Subject: Re: [PATCH] iotests/108: probe loop device setup Message-ID: References: <20261013182804.103882-1-iii@linux.ibm.com> <83590b67-3a00-4534-a4e8-9ccf335ddf31@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <83590b67-3a00-4534-a4e8-9ccf335ddf31@linux.ibm.com> User-Agent: NeoMutt/20260616 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.24, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 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: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Oct 13, 2026 at 09:08:17PM +0200, Ilya Leoshkevich wrote: > > > On 10/13/26 20:53, Eric Blake wrote: > > On Tue, Oct 13, 2026 at 08:28:00PM +0200, Ilya Leoshkevich wrote: > > > Running iotests/108 in a Docker container, that has passwordless sudo > > > configured, fails with: > > > > > > losetup: /home/user/src/qemu/build/scratch/qcow2-file-108/t.qcow2: failed to set up loop device: No such file or directory > > > > > > because it incorrectly assumes losetup is allowed to do loop device > > > setup, when in reality it can only list devices. > > > > > > Fix by probing loop device setup, using the test script as a backing > > > file. With this, the test is correctly skipped. > > > > > > Signed-off-by: Ilya Leoshkevich > > > --- > > > tests/qemu-iotests/108 | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/tests/qemu-iotests/108 b/tests/qemu-iotests/108 > > > index 1de718188aa..adbaaf87095 100755 > > > --- a/tests/qemu-iotests/108 > > > +++ b/tests/qemu-iotests/108 > > > @@ -53,7 +53,8 @@ _supported_os Linux > > > _unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file > > > # This test either needs sudo -n losetup or FUSE exports to work > > > -if sudo -n losetup &>/dev/null; then > > > +if probe_dev=$(sudo -n losetup -r --show -f "$0" 2>/dev/null); then > > > + sudo -n losetup -d "$probe_dev" > > > > Is 'sudo -n losetup -f' a simpler test? It prints out the next > > /dev/loopN value available only if a mount would succeed, which means > > that it is a stronger test than the existing 'sudo -n losetup', but > > also does not require a subsequent cleanup. > > I don't think 'losetup -f' attempts a mount, since it works fine without > privileges: > > $ id -u > 1000 > $ losetup -f > /dev/loop0 > $ losetup -r -f /bin/true > losetup: /bin/true: failed to set up loop device: Permission denied Thanks for testing. In that case, I think your longer version is reasonable. Reviewed-by: Eric Blake > > A quick glance at the source code [1] seems to confirm this: the > iterator is immediately discarded after finding a free device name. > The loop-control logic above looks similar. > > [1] > https://github.com/util-linux/util-linux/blob/v2.42.4/lib/loopdev.c#L1760 > -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org