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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 517C2C10DCE for ; Fri, 13 Mar 2020 13:06:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 201A120724 for ; Fri, 13 Mar 2020 13:06:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="auHv9EX/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726642AbgCMNGp (ORCPT ); Fri, 13 Mar 2020 09:06:45 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:23439 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726479AbgCMNGp (ORCPT ); Fri, 13 Mar 2020 09:06:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1584104804; 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: in-reply-to:in-reply-to:references:references; bh=1UcD6SvRQdQ67CEbuSkOopYlp5LyOHtadTTVCjBN5DQ=; b=auHv9EX/r8p94497cTXVepYRg06v8oXhjaQgQHf+ewK9S/BSrdDbbxGvlEHxjtjB4s6kft MQNuiOCrRnD6AMfdgG3t4KtNeIEOpLb3OVFSNSNkL6RZsr5wYfF7qYjjT7c8pIW7qCqoAi rfMwDBDtUNdwA8JD2JaZ9QUptgJK2RE= 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-252-w0ujB9D1MISbTMZ9YA7J0w-1; Fri, 13 Mar 2020 09:06:38 -0400 X-MC-Unique: w0ujB9D1MISbTMZ9YA7J0w-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8799B1088380; Fri, 13 Mar 2020 13:06:36 +0000 (UTC) Received: from localhost (ovpn-121-102.rdu2.redhat.com [10.10.121.102]) by smtp.corp.redhat.com (Postfix) with ESMTP id EBBF08B570; Fri, 13 Mar 2020 13:06:34 +0000 (UTC) Date: Fri, 13 Mar 2020 10:06:34 -0300 From: Bruno Meneguele To: David Laight Cc: Sergey Senozhatsky , "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 Message-ID: <20200313130634.GJ13406@glitch> References: <20200313003533.2203429-1-bmeneg@redhat.com> <20200313073425.GA219881@google.com> <20200313110229.GI13406@glitch> MIME-Version: 1.0 In-Reply-To: X-PGP-Key: http://keys.gnupg.net/pks/lookup?op=get&search=0x3823031E4660608D X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="FCKy2vjPBX+S/5dE" Content-Disposition: inline Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org --FCKy2vjPBX+S/5dE Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Mar 13, 2020 at 11:06:42AM +0000, David Laight wrote: > 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 ret= urn 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 document= ed. > > > > > > > > > > Hmm. I don't think I see ESPIPE in documentation [0], [1], [2] > > > > > > [0] https://pubs.opengroup.org/onlinepubs/9699919799/functions/fprint= f.html > > > [1] http://man7.org/linux/man-pages/man3/dprintf.3p.html > > > [2] http://man7.org/linux/man-pages/man3/fprintf.3p.html > > > > > > =09-ss > > > > >=20 > > Ok, I poorly expressed the notion of "documentantion". The userspace > > doesn't tell about returning -ESPIPE, but to the functions work properl= y > > they watch for -ESPIPE returning from the syscall. For instance, gblic > > dprintf() implementation: > >=20 > > dprintf: > > __vdprintf_internal: > > _IO_new_file_attach: > >=20 > > if (_IO_SEEKOFF (fp, (off64_t)0, _IO_seek_cur, _IOS_INPUT|_IOS_OUTPUT= ) > > =3D=3D _IO_pos_BAD && errno !=3D ESPIPE) > > return NULL; >=20 > 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. >=20 > =09David >=20 dprintf gets a fd as input and convert it to a FILE structure, with that it can't garantuee the previous state of that fd: was it already manipulated? Thus they check the current position to make sure it's not junk. But that's me guessing things about a code from 1996 :). --=20 bmeneg=20 PGP Key: http://bmeneg.com/pubkey.txt --FCKy2vjPBX+S/5dE Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEdWo6nTbnZdbDmXutYdRkFR+RokMFAl5rhVkACgkQYdRkFR+R okPciQf/aHCBcLzuwwtWOV0265ILqVZ/Oq9rjX1HxAgz3sMWEdov7F9qg1fyNfye 1iqo0sRROWcxzBQ4/Dvn841x4w1jLOxSRzEfZEqvzj7ybd9U1fMmZ7rGd0KosvPj agNO/lV89KHw5FX4PNcuX/CFjGDYXlWNxd1jIbtweob8QhbwsAiaWrGXiNm0oaBb CDRFqVwY1rX9LgmDugO5f8Qmwn0EHSZKgX8L2JvxdC2Nrw9bwfuufpiXVt+66cuF iHKczLsVtDcBinWIe9CWUX+k+oc2yvRdbAxFJwI7o3qCyyl0CzqJeS42BsDr28+D hgryRL1UvP3s2MmGiIfXcQA9u1OlfA== =TMYJ -----END PGP SIGNATURE----- --FCKy2vjPBX+S/5dE--