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 04281C433ED for ; Thu, 29 Apr 2021 15:36:57 +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 4ED9961154 for ; Thu, 29 Apr 2021 15:36:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4ED9961154 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]:58930 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lc8il-0005mC-6R for qemu-devel@archiver.kernel.org; Thu, 29 Apr 2021 11:36:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35616) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lc8hU-00059T-DA for qemu-devel@nongnu.org; Thu, 29 Apr 2021 11:35:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:21621) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lc8hQ-00082w-U3 for qemu-devel@nongnu.org; Thu, 29 Apr 2021 11:35:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619710532; h=from:from:reply-to: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=T6Kk6+xb7JQr17QPtqGs0ySOH81cRORD5PHau7lsjfc=; b=QIHLPdA7rC+uwsU55sn8H7pCDhCCo/8QceyeRMP43G4VeoiQ8C/qmB7IydFbvVMYYHzSt/ OVtRL8B3oAsHtgfZC47L1tgKQu/CkhCf57KLVneCT+LHAW83OnO5PAfAIT5wrWRTOiaazI kVD/hZtKE+gHobhy0nR7vQOtcBsGd8E= 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-198-nI282zTpNFy-bLVh9flkGg-1; Thu, 29 Apr 2021 11:35:28 -0400 X-MC-Unique: nI282zTpNFy-bLVh9flkGg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9D98D8797F7; Thu, 29 Apr 2021 15:35:27 +0000 (UTC) Received: from redhat.com (ovpn-115-232.ams2.redhat.com [10.36.115.232]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9C90B19C59; Thu, 29 Apr 2021 15:35:17 +0000 (UTC) Date: Thu, 29 Apr 2021 16:35:14 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Richard W.M. Jones" Subject: Re: [ANNOUNCE] libblkio v0.1.0 preview release Message-ID: References: <20210429142259.GR26415@redhat.com> <20210429150038.GT26415@redhat.com> <20210429153141.GW26415@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210429153141.GW26415@redhat.com> User-Agent: Mutt/2.0.6 (2021-03-06) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@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=unavailable 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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 04:31:41PM +0100, Richard W.M. Jones wrote: > 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. Is dlclose() really that important ? libnbd is such a small thing that i doubt anyone will even notice the space being consumed if you mark it nodelete, and if an app is repeatedly doing an op that triggers dlopen+dlclose many times, then dlclose is especially useless. Personally I think removing memory leaks on thread exit is more important than honouring dlclose, as some apps can do pathelogical things creating *many* very short lived threads. 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 :|