Received: by 2002:ad5:474a:0:0:0:0:0 with SMTP id i10csp7980271imu; Fri, 28 Dec 2018 08:22:21 -0800 (PST) X-Google-Smtp-Source: ALg8bN7VSMFioswrSj4Daw97/ZLGg7FqW5zXfBZsIah9wWVLBBz4enOD3Wl2JxXNvbtIRrXIT05V X-Received: by 2002:a17:902:2c03:: with SMTP id m3mr26885142plb.6.1546014141357; Fri, 28 Dec 2018 08:22:21 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1546014141; cv=none; d=google.com; s=arc-20160816; b=ZSa460o50j8goQbKx5/qTnG4T5nF/fvXxU0rrM1KVnPMDiXau41QNt8Rcn0/bi+dPZ UsZ8pLJfCjP4re/tvL1ztxX2sdUKlE/sRo5rXvxl5Z2Zy10APl6NcR6ZZ6Pv1Re7feVP 3WwyOMYRpUHXbmydaIfSsC7wJghyTu1s6a/FeYeS1wcVr9tEFTJnm1yYIGKSHQlexF4W oi4U6vHnsRgDf11g/gjvFDzndYfWv2Aw2DkLMcU9wLE14ZBpBxBfoF5dtLZ3r360JnNn oajXitZmJXrrLk4nWmEN16VJ5+rBQRMddSnRI1vreGpluGSjMptXc1Jbf0eWbm4uE1t6 nZdQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:mime-version:message-id:in-reply-to:date :references:subject:cc:to:from; bh=hfnrORq0JW8+ZPftt/vmTOqQXU8ywzQC713vOK/Gw68=; b=TqM+O+ofVWeEyn1w58Ylx33LkUMGiHuq8nt4gixvaQwq8YiQwDq7RL1LR5BxI5JY/7 nS7BeeLChPRrBChkJFIoNXtotJITnMDUditH2ZoV9+hhZBdpoLIuGpIpP5fmpopdds03 kapHFFhWEH266o6U0wfQcSsRmEs4TRhLBDzs4JWmPG17uIqY0LaXBMhZH3UfF0kofM/G 6CHDaxNbeaqFkWGA48mP3jwDMj92ZSxPTU0Np7lz/dqIbGlMq6bAkV28ku2Z0SG99LFF t6apUm55+ZyqXLigSYPFmhKFf5C4m1rzHdfT9G83HMsy2UIZFWDs80m04855qS2RMOEU ZqeQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id n12si23608491pfg.155.2018.12.28.08.22.05; Fri, 28 Dec 2018 08:22:21 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731795AbeL1Hqf (ORCPT + 99 others); Fri, 28 Dec 2018 02:46:35 -0500 Received: from albireo.enyo.de ([5.158.152.32]:52790 "EHLO albireo.enyo.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729313AbeL1Hqf (ORCPT ); Fri, 28 Dec 2018 02:46:35 -0500 Received: from [172.17.203.2] (helo=deneb.enyo.de) by albireo.enyo.de with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) id 1gcmqk-00059a-1l; Fri, 28 Dec 2018 07:46:30 +0000 Received: from fw by deneb.enyo.de with local (Exim 4.89) (envelope-from ) id 1gcmin-0001pk-T5; Fri, 28 Dec 2018 08:38:17 +0100 From: Florian Weimer To: "Dmitry V. Levin" Cc: linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, libc-alpha@sourceware.org, qemu-devel@nongnu.org, ericvh@gmail.com, rminnich@sandia.gov, lucho@ionkov.net, hpa@zytor.com, arnd@arndb.de Subject: Re: d_off field in struct dirent and 32-on-64 emulation References: <87bm56vqg4.fsf@mid.deneb.enyo.de> <20181228022338.GA27992@altlinux.org> Date: Fri, 28 Dec 2018 08:38:17 +0100 In-Reply-To: <20181228022338.GA27992@altlinux.org> (Dmitry V. Levin's message of "Fri, 28 Dec 2018 05:23:39 +0300") Message-ID: <87bm56w17a.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Dmitry V. Levin: > On Thu, Dec 27, 2018 at 06:18:19PM +0100, Florian Weimer wrote: >> We have a bit of an interesting problem with respect to the d_off >> field in struct dirent. >> >> When running a 64-bit kernel on certain file systems, notably ext4, >> this field uses the full 63 bits even for small directories (strace -v >> output, wrapped here for readability): >> >> getdents(3, [ >> {d_ino=1494304, d_off=3901177228673045825, d_reclen=40, >> d_name="authorized_keys", d_type=DT_REG}, >> {d_ino=1494277, d_off=7491915799041650922, d_reclen=24, >> d_name=".", d_type=DT_DIR}, >> {d_ino=1314655, d_off=9223372036854775807, d_reclen=24, >> d_name="..", d_type=DT_DIR} >> ], 32768) = 88 >> >> When running in 32-bit compat mode, this value is somehow truncated to >> 31 bits, for both the getdents and the getdents64 (!) system call (at >> least on i386). > > Why getdents64 system call is affected by this truncation, > isn't it a kernel bug that has to be fixed in the kernel instead? It's required because POSIX specifies that telldir and seekdir use long int (and not off_t) as the seek offset. If the kernel does not truncate while keeping a useful value, these functions would turn unusable.