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 86EBCC77B75 for ; Tue, 18 Apr 2023 08:56:22 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1poh7u-0002kL-6M; Tue, 18 Apr 2023 04:55:50 -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 1poh7s-0002jC-BX for qemu-devel@nongnu.org; Tue, 18 Apr 2023 04:55:48 -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 1poh7q-0003xk-Mi for qemu-devel@nongnu.org; Tue, 18 Apr 2023 04:55:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1681808144; 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:in-reply-to:in-reply-to: references:references; bh=Fax/XzDKkCw9nqBNDOZ0a6KOQzd1j5upHyzEU4KFFlw=; b=gG38PsI2Bv+pwoIwOGMa3bvs2pt9ZgQsIkkvftwazz2PPqBKmI8h7uNr1rVfV7H4fdpkGE 7sa8PNw5cbtsvzuPp4/GCxKR5qXur4BtZZfYQdGNQP5o3EuTtNRgvi5QU9vEoiUYYYMRfD 0pvzI/M1oQhQ/yFo2+w8mMHXZq4l74A= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-222-7ejcou7CMGCLUGqLtRP1ig-1; Tue, 18 Apr 2023 04:55:37 -0400 X-MC-Unique: 7ejcou7CMGCLUGqLtRP1ig-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C01EE280D583; Tue, 18 Apr 2023 08:55:36 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.65]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 254C340C6E6F; Tue, 18 Apr 2023 08:55:35 +0000 (UTC) Date: Tue, 18 Apr 2023 09:55:34 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Bin Meng Cc: Jason Wang , qemu-devel@nongnu.org, Zhangjin Wu Subject: Re: [PATCH] net: tap: Drop the close of fds for child process Message-ID: References: <20230406112041.798585-1-bmeng@tinylab.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230406112041.798585-1-bmeng@tinylab.org> User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham 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 Thu, Apr 06, 2023 at 07:20:41PM +0800, Bin Meng wrote: > Current codes using a brute-force traversal of all file descriptors > do not scale on a system where the maximum number of file descriptors > are set to a very large value (e.g.: in a Docker container of Manjaro > distribution it is set to 1073741816). QEMU just looks freezed during > start-up. > > The close-on-exec flag was introduced since a faily old Linux kernel > (2.6.23). With recent newer kernels that QEMU supports, we don't need > to manually close the fds for child process as the proper O_CLOEXEC > flag should have been set properly on files that we don't want child > process to see. Even though O_CLOEXEC has existed for a long time, there is plenty of code that doesn't use it reliably. While QEMU can control its own code, we use a huge number of 3rd party libraries and we don't trust them to reliably be using O_CLOEXEC on everything they open. > Reported-by: Zhangjin Wu > Signed-off-by: Bin Meng > --- > > net/tap.c | 14 -------------- > 1 file changed, 14 deletions(-) > > diff --git a/net/tap.c b/net/tap.c > index 1bf085d422..49e1915484 100644 > --- a/net/tap.c > +++ b/net/tap.c > @@ -446,13 +446,6 @@ static void launch_script(const char *setup_script, const char *ifname, > return; > } > if (pid == 0) { > - int open_max = sysconf(_SC_OPEN_MAX), i; > - > - for (i = 3; i < open_max; i++) { > - if (i != fd) { > - close(i); > - } > - } > parg = args; > *parg++ = (char *)setup_script; > *parg++ = (char *)ifname; > @@ -536,17 +529,10 @@ 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); > - } > - } BSD has closefrom(3) we could use here, while modern Linux has close_range(3, open_max) We should probe for those two funtions and use them preferentially, only falling back to the current manual loop where they don't exist. > - > fd_buf = g_strdup_printf("%s%d", "--fd=", sv[1]); > > if (strrchr(helper, ' ') || strrchr(helper, '\t')) { > -- > 2.34.1 > > 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 :|