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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 8408DC433DB for ; Fri, 29 Jan 2021 10:19:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 365F364E28 for ; Fri, 29 Jan 2021 10:19:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232330AbhA2KOS convert rfc822-to-8bit (ORCPT ); Fri, 29 Jan 2021 05:14:18 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:53788 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232535AbhA2KIF (ORCPT ); Fri, 29 Jan 2021 05:08:05 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-137-v6Jt3agKMwqMraTT9paTTw-1; Fri, 29 Jan 2021 09:41:42 +0000 X-MC-Unique: v6Jt3agKMwqMraTT9paTTw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 29 Jan 2021 09:41:36 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 29 Jan 2021 09:41:36 +0000 From: David Laight To: 'Lennert Buytenhek' , Al Viro CC: Jens Axboe , "linux-kernel@vger.kernel.org" , "io-uring@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-btrfs@vger.kernel.org" Subject: RE: [RFC PATCH] io_uring: add support for IORING_OP_GETDENTS64 Thread-Topic: [RFC PATCH] io_uring: add support for IORING_OP_GETDENTS64 Thread-Index: AQHW8X6IGyYpVbXZsUSWaK/6c3T86ao3WrlQgAZW5gCAAK5iEA== Date: Fri, 29 Jan 2021 09:41:36 +0000 Message-ID: References: <20210123114152.GA120281@wantstofly.org> <20210128230710.GA190469@wantstofly.org> In-Reply-To: <20210128230710.GA190469@wantstofly.org> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org From: Lennert Buytenhek > Sent: 28 January 2021 23:07 > > On Sun, Jan 24, 2021 at 10:21:38PM +0000, David Laight wrote: > > > > One open question is whether IORING_OP_GETDENTS64 should be more like > > > pread(2) and allow passing in a starting offset to read from the > > > directory from. (This would require some more surgery in fs/readdir.c.) > > > > Since directories are seekable this ought to work. > > Modulo horrid issues with 32bit file offsets. > > The incremental patch below does this. (It doesn't apply cleanly on > top of v1 of the IORING_OP_GETDENTS patch as I have other changes in > my tree -- I'm including it just to illustrate the changes that would > make this work.) > > This change seems to work, and makes IORING_OP_GETDENTS take an > explicitly specified directory offset (instead of using the file's > ->f_pos), making it more like pread(2), and I like the change from > a conceptual point of view, but it's a bit ugly around > iterate_dir_use_ctx_pos(). Any thoughts on how to do this more > cleanly (without breaking iterate_dir() semantics)? I had a further thought... I presume the basic operation is: lock(file); do_getents(); // Updates file->offset unlock(file); Which means you can implement an offset by saving, updating and restoring file->offset while the lock is held. This is a bit like the completely broken pread() in uclibc which uses two lseek() calls to set and restore the offset. Whoever wrote that needs shooting - worse than useless. Glibc is as bad: // Don't even ask what glibc's clock_nanosleep() does, you don't want to know. while (syscall(SYS_clock_nanosleep, CLOCK_MONOTONIC, TIMER_ABSTIME, &ts, NULL) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)