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=-9.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 582A2C4363C for ; Wed, 7 Oct 2020 10:09:10 +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 B1F1B20872 for ; Wed, 7 Oct 2020 10:09:09 +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="eFoJJdC2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B1F1B20872 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]:43178 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kQ6Ng-00069L-Ic for qemu-devel@archiver.kernel.org; Wed, 07 Oct 2020 06:09:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39336) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kQ6M7-0004y8-Qp for qemu-devel@nongnu.org; Wed, 07 Oct 2020 06:07:31 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:57890) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kQ6M2-0004Sp-Je for qemu-devel@nongnu.org; Wed, 07 Oct 2020 06:07:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602065245; 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=KzTyhEwSfr6WCtBg41orXhqc6eVbnoV+QBG4W4aqFW0=; b=eFoJJdC2Nkl78CkNJp6AdMhRldu5TrRm6hNNMYtOrw4H4HPvol4xfVqJ6TaDm0iqvjlKnw UajhsVb7FIQU+Xt0LRDB4M7JnF/E5b+PpsC7dlJ6Btox12VBed3LEf4V1dq8y/uiNaqPG9 tfEJc6MtiSnfbUy+3CcwYFzjQqOm4ew= 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-387-HcfG7RJnN8uaq9AHmXQUwg-1; Wed, 07 Oct 2020 06:07:22 -0400 X-MC-Unique: HcfG7RJnN8uaq9AHmXQUwg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9EF5357052; Wed, 7 Oct 2020 10:07:21 +0000 (UTC) Received: from linux.fritz.box (ovpn-113-169.ams2.redhat.com [10.36.113.169]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 09D0376646; Wed, 7 Oct 2020 10:07:06 +0000 (UTC) Date: Wed, 7 Oct 2020 12:07:05 +0200 From: Kevin Wolf To: John Snow Subject: Re: [PATCH 08/20] python/machine.py: fix _popen access Message-ID: <20201007100705.GD7212@linux.fritz.box> References: <20201006235817.3280413-1-jsnow@redhat.com> <20201006235817.3280413-9-jsnow@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201006235817.3280413-9-jsnow@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/07 00:54:30 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.733, 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_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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-block@nongnu.org, Max Reitz , qemu-devel@nongnu.org, Eduardo Habkost , Cleber Rosa Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 07.10.2020 um 01:58 hat John Snow geschrieben: > As always, Optional[T] causes problems with unchecked access. Add a > helper that asserts the pipe is present before we attempt to talk with > it. > > Signed-off-by: John Snow First a question about the preexisting state: I see that after initialising self._popen once, we never reset it to None. Should we do so on shutdown? > python/qemu/machine.py | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/python/qemu/machine.py b/python/qemu/machine.py > index 3e9cf09fd2d..4e762fcd529 100644 > --- a/python/qemu/machine.py > +++ b/python/qemu/machine.py > @@ -131,7 +131,7 @@ def __init__(self, binary, args=None, wrapper=None, name=None, > # Runstate > self._qemu_log_path = None > self._qemu_log_file = None > - self._popen = None > + self._popen: Optional['subprocess.Popen[bytes]'] = None Another option that we have, especially if it's an attribute that is never reset, would be to set the attribute only when it first gets a value other than None. Accessing it while it hasn't been set yet automatically results in an AttributeError. I don't think that's much worse than the exception raised explicitly in a property wrapper. In this case, you would only declare the type in __init__, but not assign a value to it: self._popen: Optional['subprocess.Popen[bytes]'] Maybe a nicer alternative in some cases than adding properties around everything. Instead of checking for None, you would then have to use hasattr(), which is a bit uglier, so I guess it's mainly for attributes where you can assume that you will always have a value (if the caller isn't buggy) and therefore don't even have a check in most places. > self._events = [] > self._iolog = None > self._qmp_set = True # Enable QMP monitor by default. > @@ -244,6 +244,12 @@ def is_running(self): > """Returns true if the VM is running.""" > return self._popen is not None and self._popen.poll() is None > > + @property > + def _subp(self) -> 'subprocess.Popen[bytes]': > + if self._popen is None: > + raise QEMUMachineError('Subprocess pipe not present') > + return self._popen > + > def exitcode(self): > """Returns the exit code if possible, or None.""" > if self._popen is None: Of course, even if an alternative is possible, what you have is still correct. Reviewed-by: Kevin Wolf