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 070CFC00307 for ; Fri, 6 Sep 2019 19:33:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DCF6A2070C for ; Fri, 6 Sep 2019 19:33:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393355AbfIFTdS convert rfc822-to-8bit (ORCPT ); Fri, 6 Sep 2019 15:33:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:3236 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730615AbfIFTdS (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 704F12D6A3F for ; Fri, 6 Sep 2019 19:33:17 +0000 (UTC) Received: by mail-wr1-f72.google.com with SMTP id j10so2978088wrb.16 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=n3kD2F2Bp950JftWsKUFB4YdTeSS4bHygWe4KQ+oi0JROaCdw9fmPwUaltI8PkQT+U YYCdDtXLAvVQt5Pcl8y6Sg8j/mDJNID6nADCx3iTIC67G7xmS1oMgkTsiMwVX08R8VBF H7oHKmmxqQjX3e+sjtoJs434eCFz+99Q6ZjV61h7lkLoN5ZJa2wyRSOknBpjWeLFOqT0 EqmwERIP6AzZKDWk1akbGwe21VUfT0Y4tgVF09NqzCrSBrI5DiN76Xb4Nmnq4L1bD1RL s7/AKWb76dhAA4WzlUbOXvJ0hQWyeLHjbRYlPQeG73TPA5nh/Clunvpk/PpuSEDNkoSe 547Q== X-Gm-Message-State: APjAAAVbfVptqpPYrp1IStF4iQ5pll+swdXcPgeW1kRYnXuzit0Zk1lc Kt9U4aReQ4w8wWjXwdEcjEDyvtu5d3sQ4ar2hdRKX6ZZevS21D6KjX7I9ecKF++qa0djepquQ4a bvFNy+QHA/1cJtj/DzckXFZ3tgtjZDa9NxWK+ X-Received: by 2002:a1c:ca02:: with SMTP id a2mr9252541wmg.127.1567798396045; 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-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@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