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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 329F9C4CECE for ; Fri, 13 Mar 2020 11:06:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1756E206E2 for ; Fri, 13 Mar 2020 11:06:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726546AbgCMLGr convert rfc822-to-8bit (ORCPT ); Fri, 13 Mar 2020 07:06:47 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:49561 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726488AbgCMLGq (ORCPT ); Fri, 13 Mar 2020 07:06:46 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-80-gv2f1hCOODeqrgtDqydigQ-1; Fri, 13 Mar 2020 11:06:42 +0000 X-MC-Unique: gv2f1hCOODeqrgtDqydigQ-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, 13 Mar 2020 11:06:42 +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, 13 Mar 2020 11:06:42 +0000 From: David Laight To: 'Bruno Meneguele' , Sergey Senozhatsky CC: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , "pmladek@suse.com" , "sergey.senozhatsky@gmail.com" , "rostedt@goodmis.org" Subject: RE: [PATCH] kernel/printk: add kmsg SEEK_CUR handling Thread-Topic: [PATCH] kernel/printk: add kmsg SEEK_CUR handling Thread-Index: AQHV+SbtOwT0X58SokiO9wU0er7wyahGXCjQ Date: Fri, 13 Mar 2020 11:06:42 +0000 Message-ID: References: <20200313003533.2203429-1-bmeneg@redhat.com> <20200313073425.GA219881@google.com> <20200313110229.GI13406@glitch> In-Reply-To: <20200313110229.GI13406@glitch> Accept-Language: en-GB, en-US Content-Language: 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 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Bruno Meneguele > Sent: 13 March 2020 11:02 > On Fri, Mar 13, 2020 at 04:34:25PM +0900, Sergey Senozhatsky wrote: > > On (20/03/12 21:35), Bruno Meneguele wrote: > > > > > > Userspace libraries, e.g. glibc's dprintf(), expect the default return value > > > for invalid seek situations: -ESPIPE, but when the IO was over /dev/kmsg the > > > current state of kernel code was returning the generic case of an -EINVAL. > > > Hence, userspace programs were not behaving as expected or documented. > > > > > > > Hmm. I don't think I see ESPIPE in documentation [0], [1], [2] > > > > [0] https://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html > > [1] http://man7.org/linux/man-pages/man3/dprintf.3p.html > > [2] http://man7.org/linux/man-pages/man3/fprintf.3p.html > > > > -ss > > > > Ok, I poorly expressed the notion of "documentantion". The userspace > doesn't tell about returning -ESPIPE, but to the functions work properly > they watch for -ESPIPE returning from the syscall. For instance, gblic > dprintf() implementation: > > dprintf: > __vdprintf_internal: > _IO_new_file_attach: > > if (_IO_SEEKOFF (fp, (off64_t)0, _IO_seek_cur, _IOS_INPUT|_IOS_OUTPUT) > == _IO_pos_BAD && errno != ESPIPE) > return NULL; Someone explain why it is doing an explicit seek to the current position? The only reason to do that is to get the current offset. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)