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=-10.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 8BF79C433B4 for ; Thu, 29 Apr 2021 15:33:42 +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 9502D61139 for ; Thu, 29 Apr 2021 15:33:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9502D61139 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]:56264 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lc8fc-0004Ss-9d for qemu-devel@archiver.kernel.org; Thu, 29 Apr 2021 11:33:40 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34574) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lc8e0-0003uN-16 for qemu-devel@nongnu.org; Thu, 29 Apr 2021 11:32:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:23926) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lc8dw-0006S4-1f for qemu-devel@nongnu.org; Thu, 29 Apr 2021 11:31:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619710308; 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=VaPoerpVO1NeuTYoTqiT9olm+bbYFth6/cdJ2kgJiSo=; b=DF5/EHWDB5ffvqJTCRl3OLwuSk+DZ3fN5J5JXPESsjFU1l4W+oHAQzkxF6Qexv3gpj9HNy /4+aCS1q//+gAtutLO6Pfkb/ybE9Zg+QsrTdGG75Z9JY91NymJyS601PdgvoR904nTTofB tGssLTPtF1mrD9Dhxr+/zoDolWg7Cwg= 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-596-Pfagu8vFPceyPgMlDhPBDg-1; Thu, 29 Apr 2021 11:31:45 -0400 X-MC-Unique: Pfagu8vFPceyPgMlDhPBDg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8B0321008064; Thu, 29 Apr 2021 15:31:43 +0000 (UTC) Received: from localhost (ovpn-114-114.ams2.redhat.com [10.36.114.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 06E9860936; Thu, 29 Apr 2021 15:31:41 +0000 (UTC) Date: Thu, 29 Apr 2021 16:31:41 +0100 From: "Richard W.M. Jones" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [ANNOUNCE] libblkio v0.1.0 preview release Message-ID: <20210429153141.GW26415@redhat.com> References: <20210429142259.GR26415@redhat.com> <20210429150038.GT26415@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=rjones@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.22, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , pkrempa@redhat.com, Alberto Garcia , slp@redhat.com, qemu-block@nongnu.org, Markus Armbruster , qemu-devel@nongnu.org, mreitz@redhat.com, Vladimir Sementsov-Ogievskiy , Stefan Hajnoczi , Klaus Jensen , philmd@redhat.com, sgarzare@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Apr 29, 2021 at 04:08:22PM +0100, Daniel P. Berrangé wrote: > On Thu, Apr 29, 2021 at 04:00:38PM +0100, Richard W.M. Jones wrote: > > On Thu, Apr 29, 2021 at 03:41:29PM +0100, Stefan Hajnoczi wrote: > > > On Thu, Apr 29, 2021 at 03:22:59PM +0100, Richard W.M. Jones wrote: > > > > On Thu, Apr 29, 2021 at 03:05:50PM +0100, Stefan Hajnoczi wrote: > > > > > The purpose of this preview release is to discuss both the API design > > > > > and general direction of the project. API documentation is available > > > > > here: > > > > > > > > > > https://gitlab.com/libblkio/libblkio/-/blob/v0.1.0/docs/blkio.rst > > > > > > > > libvirt originally, and now libnbd, keep a per-thread error message > > > > (stored in thread-local storage). It's a lot nicer than having to > > > > pass &errmsg to every function. You can just write: > > > > > > > > if (nbd_connect_tcp (nbd, "remote", "nbd") == -1) { > > > > fprintf (stderr, > > > > "failed to connect to remote server: %s (errno = %d)\n", > > > > nbd_get_error (), nbd_get_errno ()); > > > > exit (EXIT_FAILURE); > > > > } > > > > > > > > (https://libguestfs.org/libnbd.3.html#ERROR-HANDLING) > > > > > > > > It means you can extend the range of error information available in > > > > future. Also you can return a 'const char *' and the application > > > > doesn't have to worry about lifetimes, at least in the common case. > > > > > > Thanks for sharing the idea, I think it would work well for libblkio > > > too. > > > > > > Do you ignore the dlclose(3) memory leak? > > > > I believe this mechanism in libnbd ensures there is no leak in the > > ordinary shared library (not dlopen/dlclose) case: > > > > https://gitlab.com/nbdkit/libnbd/-/blob/f9257a9fdc68706a4079deb4ced61e1d468f28d6/lib/errors.c#L35 > > > > However I'm not sure what happens in the dlopen case, so I'm going to > > test that out now ... > > pthread_key destructors are a disaster waiting to happen with > dlclose, if the dlclose happens while non-main threads are > still running. When those threads exit, they'll run the > destructor which points to a function that is no longer > resident in memory. > > IOW if you have destrutors, then you need to make sure your > library uses "-z nodelete" when linking, to turn dlclose() > into a no-op. I suspect letting the string leak is a better idea for libnbd. Still trying to write a nice reproducer .. Rich. > commit 8e44e5593eb9b89fbc0b54fde15f130707a0d81e > Author: Daniel P. Berrangé > Date: Thu Sep 1 17:57:06 2011 +0100 > > Prevent crash from dlclose() of libvirt.so > > When libvirt calls virInitialize it creates a thread local > for the virErrorPtr storage, and registers a callback to > cleanup memory when a thread exits. When libvirt is dlclose()d > or otherwise made non-resident, the callback function is > removed from memory, but the thread local may still exist > and if a thread later exists, it will invoke the callback > and SEGV. There may also be other thread locals with callbacks > pointing to libvirt code, so it is in general never safe to > unload libvirt.so from memory once initialized. > > To allow dlclose() to succeed, but keep libvirt.so resident > in memory, link with '-z nodelete'. This issue was first > found with the libvirt CIM provider, but can potentially > hit many of the dynamic language bindings which all ultimately > involve dlopen() in some way, either on libvirt.so itself, > or on the glue code for the binding which in turns links > to libvirt > > > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v