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[209.85.208.174]) by smtp.gmail.com with ESMTPSA id f5sm1239997lfh.52.2019.09.06.10.15.04 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Sep 2019 10:15:04 -0700 (PDT) Received: by mail-lj1-f174.google.com with SMTP id l20so6708368ljj.3 for ; Fri, 06 Sep 2019 10:15:04 -0700 (PDT) X-Received: by 2002:a2e:8507:: with SMTP id j7mr6626752lji.156.1567790104003; Fri, 06 Sep 2019 10:15:04 -0700 (PDT) MIME-Version: 1.0 References: <156763534546.18676.3530557439501101639.stgit@warthog.procyon.org.uk> <17703.1567702907@warthog.procyon.org.uk> <5396.1567719164@warthog.procyon.org.uk> <14883.1567725508@warthog.procyon.org.uk> <27732.1567764557@warthog.procyon.org.uk> <8e60555e-9247-e03f-e8b4-1d31f70f1221@redhat.com> In-Reply-To: From: Linus Torvalds Date: Fri, 6 Sep 2019 10:14:47 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Why add the general notification queue and its sources To: Steven Whitehouse Cc: David Howells , Ray Strode , Greg Kroah-Hartman , 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" Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Sep 6, 2019 at 10:07 AM Linus Torvalds wrote: > > Hmm. Maybe somebody can come up with a good legacy signaling solution > (and "just use another pipe for error notification and OOB data" for > the first one may _work_, but that sounds pretty hacky and just not > very convenient). ... actually, maybe the trivial solution for at least some prototyping cases is to make any user mode writers never drop messages. Don't use a non-blocking fd for the write direction. That's obviously *not* acceptable for a kernel writer, and it's not acceptable for an actual system daemon writer (that you could block by just not reading the notifications), but it's certainly acceptable for the "let's prototype having kernel support for /proc/mounts notifications using a local thread that just polls for it every few seconds". So at least for _some_ prototypes you can probably just ignore the overflow issue. It won't get you full test coverage, but it will get you a working legacy solution and a "look, if we have kernel support for this, we can do better". Linus