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[23.128.96.18]) by mx.google.com with ESMTP id z4si6246863eji.462.2020.09.20.11.43.06; Sun, 20 Sep 2020 11:43:31 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726267AbgITSmG (ORCPT + 99 others); Sun, 20 Sep 2020 14:42:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726055AbgITSmG (ORCPT ); Sun, 20 Sep 2020 14:42:06 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D4B81C061755; Sun, 20 Sep 2020 11:42:05 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kK4Hd-002cE4-T4; Sun, 20 Sep 2020 18:41:58 +0000 Date: Sun, 20 Sep 2020 19:41:57 +0100 From: Al Viro To: Matthew Wilcox Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag Message-ID: <20200920184157.GP3421308@ZenIV.linux.org.uk> References: <20200918124533.3487701-1-hch@lst.de> <20200918124533.3487701-2-hch@lst.de> <20200920151510.GS32101@casper.infradead.org> <20200920180742.GN3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200920180742.GN3421308@ZenIV.linux.org.uk> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 20, 2020 at 07:07:42PM +0100, Al Viro wrote: > /proc/bus/input/devices (fucked bitmap-to-text representation) To illustrate the, er, beauty of that stuff: ; cat32 /proc/bus/input/devices >/tmp/a ; cat /proc/bus/input/devices >/tmp/b ; diff -u /tmp/a /tmp/b|grep '^[-+]' --- /tmp/a 2020-09-20 14:28:43.442560691 -0400 +++ /tmp/b 2020-09-20 14:28:49.018543230 -0400 -B: KEY=1100f 2902000 8380307c f910f001 feffffdf ffefffff ffffffff fffffffe +B: KEY=1100f02902000 8380307cf910f001 feffffdfffefffff fffffffffffffffe -B: KEY=70000 0 0 0 0 0 0 0 0 +B: KEY=70000 0 0 0 0 -B: KEY=420 0 70000 0 0 0 0 0 0 0 0 +B: KEY=420 70000 0 0 0 0 -B: KEY=100000 0 0 0 +B: KEY=10000000000000 0 -B: KEY=4000 0 0 0 0 +B: KEY=4000 0 0 -B: KEY=8000 0 0 0 0 0 1100b 800 2 200000 0 0 0 0 +B: KEY=800000000000 0 0 1100b00000800 200200000 0 0 -B: KEY=3e000b 0 0 0 0 0 0 0 +B: KEY=3e000b00000000 0 0 0 -B: KEY=ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff fffffffe +B: KEY=ffffffffffffffff ffffffffffffffff ffffffffffffffff fffffffffffffffe ; (cat32 being a 32bit binary of cat) All the differences are due to homegrown bitmap-to-text conversion. Note that feeding that into a pipe leaves the recepient with a lovely problem - you can't go by the width of words (they are not zero-padded) and you can't go by the number of words either - it varies from device to device. And there's nothing we can do with that - it's a userland ABI, can't be changed without breaking stuff. I would prefer to avoid additional examples like that, TYVM...