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=-8.3 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 D431DC04A6B for ; Wed, 8 May 2019 09:05:18 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A8F53214C6 for ; Wed, 8 May 2019 09:05:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A8F53214C6 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 ([127.0.0.1]:33504 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOIVp-0006EA-Ue for qemu-devel@archiver.kernel.org; Wed, 08 May 2019 05:05:17 -0400 Received: from eggs.gnu.org ([209.51.188.92]:43083) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOISO-0003ug-Ia for qemu-devel@nongnu.org; Wed, 08 May 2019 05:01:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hOISM-0006dw-Iu for qemu-devel@nongnu.org; Wed, 08 May 2019 05:01:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48420) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hOISG-0006Z9-QA; Wed, 08 May 2019 05:01:37 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 805383084213; Wed, 8 May 2019 09:01:35 +0000 (UTC) Received: from redhat.com (unknown [10.42.22.189]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2160260C6A; Wed, 8 May 2019 09:01:33 +0000 (UTC) Date: Wed, 8 May 2019 10:01:31 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Max Reitz Message-ID: <20190508090131.GA32552@redhat.com> References: <20190507183610.9848-1-mreitz@redhat.com> <20190507183610.9848-2-mreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190507183610.9848-2-mreitz@redhat.com> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Wed, 08 May 2019 09:01:35 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 1/5] qemu-nbd: Add --pid-file option X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Kevin Wolf , qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, May 07, 2019 at 08:36:06PM +0200, Max Reitz wrote: > --fork is a bit boring if there is no way to get the child's PID. This > option helps. > > Signed-off-by: Max Reitz > --- > qemu-nbd.c | 29 +++++++++++++++++++++++++++++ > qemu-nbd.texi | 2 ++ > 2 files changed, 31 insertions(+) > > diff --git a/qemu-nbd.c b/qemu-nbd.c > index dca9e72cee..7e48154f44 100644 > --- a/qemu-nbd.c > +++ b/qemu-nbd.c > @@ -59,6 +59,7 @@ > #define QEMU_NBD_OPT_IMAGE_OPTS 262 > #define QEMU_NBD_OPT_FORK 263 > #define QEMU_NBD_OPT_TLSAUTHZ 264 > +#define QEMU_NBD_OPT_PID_FILE 265 > > #define MBR_SIZE 512 > > @@ -111,6 +112,7 @@ static void usage(const char *name) > " specify tracing options\n" > " --fork fork off the server process and exit the parent\n" > " once the server is running\n" > +" --pid-file=PATH store the server's process ID in the given file\n" > #if HAVE_NBD_DEVICE > "\n" > "Kernel NBD client support:\n" > @@ -651,6 +653,7 @@ int main(int argc, char **argv) > { "image-opts", no_argument, NULL, QEMU_NBD_OPT_IMAGE_OPTS }, > { "trace", required_argument, NULL, 'T' }, > { "fork", no_argument, NULL, QEMU_NBD_OPT_FORK }, > + { "pid-file", required_argument, NULL, QEMU_NBD_OPT_PID_FILE }, > { NULL, 0, NULL, 0 } > }; > int ch; > @@ -677,6 +680,8 @@ int main(int argc, char **argv) > bool list = false; > int old_stderr = -1; > unsigned socket_activation; > + const char *pid_path = NULL; > + FILE *pid_file; > > /* The client thread uses SIGTERM to interrupt the server. A signal > * handler ensures that "qemu-nbd -v -c" exits with a nice status code. > @@ -876,6 +881,9 @@ int main(int argc, char **argv) > case 'L': > list = true; > break; > + case QEMU_NBD_OPT_PID_FILE: > + pid_path = optarg; > + break; > } > } > > @@ -1196,6 +1204,27 @@ int main(int argc, char **argv) > > nbd_update_server_watch(); > > + if (pid_path) { > + pid_file = fopen(pid_path, "w"); > + if (!pid_file) { > + error_report("Failed to store PID in %s: %s", > + pid_path, strerror(errno)); > + exit(EXIT_FAILURE); > + } > + > + ret = fprintf(pid_file, "%ld", (long)getpid()); > + if (ret < 0) { > + ret = -errno; > + } > + fclose(pid_file); > + > + if (ret < 0) { > + error_report("Failed to store PID in %s: %s", > + pid_path, strerror(-ret)); > + exit(EXIT_FAILURE); > + } > + } This is racy because multiple qemu-nbd's can be started pointing to the same pidfile and one will blindly overwrite the other. Please use qemu_write_pidfile instead which acquires locks on the pidfile in a race free manner. 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 :|