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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id E9193C27C79 for ; Mon, 17 Jun 2024 16:40:24 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sJFOw-00044m-7p; Mon, 17 Jun 2024 12:40:14 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sJFOn-00044D-Ba for qemu-devel@nongnu.org; Mon, 17 Jun 2024 12:40:06 -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 1sJFOl-0006KV-L6 for qemu-devel@nongnu.org; Mon, 17 Jun 2024 12:40:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1718642403; 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=68yhaLWk4hWAgeJm/xA8eTKxA7oWV9yEcuUHYr1Fk4w=; b=DBJzK9ZiGyTwihzvWRc2EsO4UKUj8hgJDbbPXVg1U4MIijpDUsHwUp70vPK2jbSvxEf5P/ LpQ7xfq7WkUkDKJyVFLGd+veAK1jJa029GDg9XqjoW3fNYoKJU8IzxjkXdsDEoZLV6oKhE YTTxJVfDcbF2ai6+jAa4YAHZjfd3KHA= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-344-q9sVLDSBMKCLe5-oLloRFg-1; Mon, 17 Jun 2024 12:39:57 -0400 X-MC-Unique: q9sVLDSBMKCLe5-oLloRFg-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0682E19560B7; Mon, 17 Jun 2024 16:39:56 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.46]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CBD2319560AE; Mon, 17 Jun 2024 16:39:54 +0000 (UTC) Date: Mon, 17 Jun 2024 17:39:51 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: =?utf-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= Cc: qemu-devel@nongnu.org Subject: Re: [PATCH] tap: use close_range() when forking scripts and helper Message-ID: References: <20240617162520.4045016-1-cleger@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240617162520.4045016-1-cleger@rivosinc.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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: 11 X-Spam_score: 1.1 X-Spam_bar: + X-Spam_report: (1.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.148, 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, RCVD_IN_SBL_CSS=3.335, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Jun 17, 2024 at 06:25:18PM +0200, Clément Léger wrote: > Since commit 03e471c41d8b ("qemu_init: increase NOFILE soft limit on > POSIX"), the maximum number of file descriptors that can be opened are > raised to nofile.rlim_max. On recent debian distro, this yield a maximum > of 1073741816 file descriptors. Now, when forking to start > qemu-bridge-helper, this actually calls close() on the full possible file > descriptor range (more precisely [3 - sysconf(_SC_OPEN_MAX)]) which > takes a considerable amount of time. Use close_range() which only > requires to be called twice and factorize it in a separate function for > both call sites. > > Signed-off-by: Clément Léger > --- > net/tap.c | 25 +++++++++++++------------ > 1 file changed, 13 insertions(+), 12 deletions(-) > > diff --git a/net/tap.c b/net/tap.c > index 51f7aec39d..6f5bf06bb5 100644 > --- a/net/tap.c > +++ b/net/tap.c > @@ -385,6 +385,17 @@ static TAPState *net_tap_fd_init(NetClientState *peer, > return s; > } > > +static void fork_close_all_fds_except(int fd) > +{ > + int open_max = sysconf(_SC_OPEN_MAX); > + > + if (fd > 3) > + close_range(3, fd - 1, 0); > + > + if (fd < open_max) > + close_range(fd + 1, open_max, 0); > +} We can't assume that 'close_range' exists on all platforms/versions that QEMU targets. In system/async-teardown.c there is close_all_open_fd() that has a fallback path to iterating over /proc, which gives good fallback for Linux. That code doesn't have to deal with non-Linux though. I'd suggest that util/osdep.c needs to have a 'close_all_open_fd()' method that accepts an array of FDs to skip closing of, rather than assuming we always skip STDIO + 1 extra FD. eg int close_all_open_fd(int *skip, int nskip); Could either declare that 'skip' must be sorted, or we can explicitly run qsort() on it. Try native close_range first. If unavailable, then on Linux try /proc, otherwise the simple for() loop. Then use this common helper from both tap.c and asynct-teardown.c > + > static void launch_script(const char *setup_script, const char *ifname, > int fd, Error **errp) > { > @@ -400,13 +411,8 @@ static void launch_script(const char *setup_script, const char *ifname, > return; > } > if (pid == 0) { > - int open_max = sysconf(_SC_OPEN_MAX), i; > + fork_close_all_fds_except(fd); > > - for (i = 3; i < open_max; i++) { > - if (i != fd) { > - close(i); > - } > - } > parg = args; > *parg++ = (char *)setup_script; > *parg++ = (char *)ifname; > @@ -490,16 +496,11 @@ static int net_bridge_run_helper(const char *helper, const char *bridge, > return -1; > } > if (pid == 0) { > - int open_max = sysconf(_SC_OPEN_MAX), i; > char *fd_buf = NULL; > char *br_buf = NULL; > char *helper_cmd = NULL; > > - for (i = 3; i < open_max; i++) { > - if (i != sv[1]) { > - close(i); > - } > - } > + fork_close_all_fds_except(sv[1]); > > fd_buf = g_strdup_printf("%s%d", "--fd=", sv[1]); > > -- > 2.45.2 > > With 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 :|