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=-5.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=no 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 EB845C433DF for ; Tue, 13 Oct 2020 00:09:41 +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 2ECD820878 for ; Tue, 13 Oct 2020 00:09:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ArQzbOgJ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2ECD820878 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]:54334 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kS7sq-0001AN-4K for qemu-devel@archiver.kernel.org; Mon, 12 Oct 2020 20:09:40 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51540) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kS7sI-0000kJ-03 for qemu-devel@nongnu.org; Mon, 12 Oct 2020 20:09:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:26190) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kS7sG-0002NL-BF for qemu-devel@nongnu.org; Mon, 12 Oct 2020 20:09:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602547743; 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=LAP1T1JAnG2HJETBGKHtI+zO8NC5NvDJAklkJA95KlI=; b=ArQzbOgJaZA5ABYdXmcW9O2hcHC3XS6KfBQVtYCCzNiuKGJEKSRFKAuIf/h/Wi73u9g3HD iKiUUpxbhFxyjZ69nGvdJW5rOjsbUq0MZPyLNtQrUymkbISKFlHVWqLuhE4boTqm17aWaY YUmXkGPKkBV9ezrmSrxTxMVHaI9c23E= 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-499-XEu3x5wSOryDNKrHD3xpGA-1; Mon, 12 Oct 2020 20:08:59 -0400 X-MC-Unique: XEu3x5wSOryDNKrHD3xpGA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D4CE71018F63; Tue, 13 Oct 2020 00:08:57 +0000 (UTC) Received: from [10.3.114.107] (ovpn-114-107.phx2.redhat.com [10.3.114.107]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5B0B65C269; Tue, 13 Oct 2020 00:08:56 +0000 (UTC) Subject: Re: [PATCH v3 RESEND] fcntl: Add 32bit filesystem mode To: Linus Walleij , Theodore Ts'o , Andreas Dilger References: <20201012220620.124408-1-linus.walleij@linaro.org> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Mon, 12 Oct 2020 19:08:55 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201012220620.124408-1-linus.walleij@linaro.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Received-SPF: pass client-ip=216.205.24.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/11 23:52:29 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, 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: Peter Maydell , linux-api@vger.kernel.org, qemu-devel@nongnu.org, Florian Weimer , Andy Lutomirski , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/12/20 5:06 PM, Linus Walleij wrote: > It was brought to my attention that this bug from 2018 was > still unresolved: 32 bit emulators like QEMU were given > 64 bit hashes when running 32 bit emulation on 64 bit systems. > > This adds a flag to the fcntl() F_GETFD and F_SETFD operations > to set the underlying filesystem into 32bit mode even if the > file handle was opened using 64bit mode without the compat > syscalls. > > Programs that need the 32 bit file system behavior need to > issue a fcntl() system call such as in this example: > > #define FD_32BIT_MODE 2 > > int main(int argc, char** argv) { > DIR* dir; > int err; > int fd; > > dir = opendir("/boot"); > fd = dirfd(dir); > err = fcntl(fd, F_SETFD, FD_32BIT_MODE); This is a blind set, and wipes out FD_CLOEXEC. Better would be to do a proper demonstration of the read-modify-write with F_GETFD that portable programs will have to use in practice. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org