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=-0.7 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 316FDC43140 for ; Fri, 6 Sep 2019 19:33:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1434F2070C for ; Fri, 6 Sep 2019 19:33:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728603AbfIFTdS convert rfc822-to-8bit (ORCPT ); Fri, 6 Sep 2019 15:33:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1177 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727143AbfIFTdS (ORCPT ); Fri, 6 Sep 2019 15:33:18 -0400 Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6585419CFF5 for ; Fri, 6 Sep 2019 19:33:17 +0000 (UTC) Received: by mail-wr1-f72.google.com with SMTP id i4so2979112wri.1 for ; Fri, 06 Sep 2019 12:33:17 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=R/U7mUhygsddH+fGB+zy3E9CKa5h+Z8Nm54osdGuOgs=; b=A9ls7pNToe55UnhVj5KpBEeynKyCY1XZRa1KFPQBKLAXZeCTzLFxYb7LvvJBCHPYy5 u48dh38/QVC2lPFUiACKxPEYYx9mlIq3R61eym6kj4JTlnOq166knTWVv6DKo/3VytBF 35QkrJQiWAyIqJs0hekPzTdj4G8jg2C1vD9UlVsYWhPmPRb+2Eb35aq/sSsC+uiMH+Mo 8hR2Kje8wIblvvHH0gi+Oyy15TUGlX+/VLnEh9xAzXQsq9LDpefbvyrscsCfG8VHR3tx VV8fIRuvSZIfxBshWk3wbLIhFM74RI0zco1QFLUe3OQ7YMCFpDsno/HHmdoaPQ6KlyF5 2hJQ== X-Gm-Message-State: APjAAAU+1A4h5AjmXPOQBkvZNcw/YEeP/Jx2Xe4SWlRqFExnUcIWcKJB gnwSzPqyWrlivVXU6Mgy6DfHn17iwdnWLJD0h+OJtbf7HchhnTd1MB6jmhBNsB5bGjDuqaxvRDQ gaZMvQkKLtZyk0LCxYl+1PmneLVQHyboMsKokKaL82g== X-Received: by 2002:a1c:ca02:: with SMTP id a2mr9252526wmg.127.1567798396043; Fri, 06 Sep 2019 12:33:16 -0700 (PDT) X-Google-Smtp-Source: APXvYqyTIyfiPV/yAsPvflKtcRM07P7nCUNe0sQoeZ2AMSNSLR0dzqdoxrOYrd5Bg/c1ZdH+IG1R0aOFq6s5vYlI0XA= X-Received: by 2002:a1c:ca02:: with SMTP id a2mr9252505wmg.127.1567798395711; Fri, 06 Sep 2019 12:33:15 -0700 (PDT) MIME-Version: 1.0 References: <156763534546.18676.3530557439501101639.stgit@warthog.procyon.org.uk> <17703.1567702907@warthog.procyon.org.uk> In-Reply-To: From: Ray Strode Date: Fri, 6 Sep 2019 15:32:37 -0400 Message-ID: Subject: Re: Why add the general notification queue and its sources To: Linus Torvalds Cc: David Howells , Greg Kroah-Hartman , Steven Whitehouse , Nicolas Dichtel , raven@themaw.net, keyrings@vger.kernel.org, linux-usb@vger.kernel.org, linux-block , Christian Brauner , LSM List , linux-fsdevel , Linux API , Linux List Kernel Mailing , Al Viro , "Ray, Debarshi" , Robbie Harwood Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi, On Thu, Sep 5, 2019 at 4:39 PM Linus Torvalds wrote: > That is *way* too specific to make for any kind of generic > notification mechanism. Well from my standpoint, I just don't want to have to poll... I don't have a strong opinion about how it looks architecturally to reach that goal. Ideally, at a higher level, I want the userspace api that gnome uses to be something like: err = krb5_cc_watch (ctx, ccache, (krb5_cc_change_fct) on_cc_change , &watch_fd); then a watch_fd would get handed back and caller could poll on it. if it woke up poll(), caller would do krb5_cc_watch_update (ctx, ccache, watch_fd) or so and it would trigger on_cc_change to get called (or something like that). If under the hood, fd comes from opening /dev/watch_queue, and krb5_cc_watch_update reads from some mmap'ed buffer to decide whether or not to call on_cc_change, that's fine with me. If under the hood, fd comes from a pipe fd returned from some ioctl or syscall, and krb5_cc_watch_update reads messages directly from that fd to decide whether or not to call on_cc_change, that's fine with me. too. it could be an eventfd too, or whatever, too, just as long as its something I can add to poll() and don't have to intermittently poll ... :-) > Also, what is the security model here? Open a special character > device, and you get access to random notifications from random > sources? I guess dhowells answered this... > And why would you do a broken big-key thing in the kernel in the first > place? Why don't you just have a kernel key to indirectly encrypt > using a key and "additional user space data". The kernel should simply > not take care of insane 1MB keys. 🤷 dunno. I assume you're referencing the discussions from comment 0 on that 2013 bug. I wasn't involved in those discussions, I just chimed in after they happened trying to avoid having to add polling :-) I have no idea why a ticket would get that large. I assume it only is in weird edge cases. Anyway, gnome treats the tickets as opaque blobs. it doesn't do anything with them other than tell the user when they need to get refreshed... all the actual key manipulation happens from krb5 libraries. of course, one advantage of having the tickets kernel side is nfs could in theory access them directly, rather than up calling back to userspace... --Ray