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=-4.1 required=3.0 tests=BAYES_00,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 22322C433E5 for ; Fri, 24 Jul 2020 11:36:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F3EEA2073E for ; Fri, 24 Jul 2020 11:36:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="QiUxsE5h" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726994AbgGXLgQ (ORCPT ); Fri, 24 Jul 2020 07:36:16 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:24037 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726953AbgGXLgO (ORCPT ); Fri, 24 Jul 2020 07:36:14 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595590573; 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=I68fbRd6bZ95LK9+jolwOQBVPAxfW2jV01rcWnCSNp0=; b=QiUxsE5hiBwr1+j9+9A4zI7TPuUTuM2MYnn90e7OYV5jLh3QfxzurpmL60vc6A3ms52vre j+UHnijDh5I2fbv/M7PFXw/GhI8YQIWkR+W8GbBqnuGIgXCB66AMoYdThyeNxV1KhN2wYD DYGnf68Iwt82eYr9qVbQZBthoTuur4M= 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-512-PexwN0WVOwWbFOVy0tM0dg-1; Fri, 24 Jul 2020 07:36:10 -0400 X-MC-Unique: PexwN0WVOwWbFOVy0tM0dg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 507C6107ACCA; Fri, 24 Jul 2020 11:36:07 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-112-32.rdu2.redhat.com [10.10.112.32]) by smtp.corp.redhat.com (Postfix) with ESMTP id EDB2919723; Fri, 24 Jul 2020 11:36:03 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <865566fb800a014868a9a7e36a00a14430efb11e.camel@themaw.net> References: <865566fb800a014868a9a7e36a00a14430efb11e.camel@themaw.net> <1293241.1595501326@warthog.procyon.org.uk> <158454378820.2863966.10496767254293183123.stgit@warthog.procyon.org.uk> <158454391302.2863966.1884682840541676280.stgit@warthog.procyon.org.uk> <2003787.1595585999@warthog.procyon.org.uk> To: Ian Kent Cc: dhowells@redhat.com, Miklos Szeredi , Linus Torvalds , Al Viro , Casey Schaufler , Stephen Smalley , nicolas.dichtel@6wind.com, Christian Brauner , andres@anarazel.de, Jeff Layton , dray@redhat.com, Karel Zak , keyrings@vger.kernel.org, Linux API , linux-fsdevel@vger.kernel.org, LSM , linux-kernel@vger.kernel.org Subject: Re: [PATCH 13/17] watch_queue: Implement mount topology and attribute change notifications [ver #5] MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <2023285.1595590563.1@warthog.procyon.org.uk> Date: Fri, 24 Jul 2020 12:36:03 +0100 Message-ID: <2023286.1595590563@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Ian Kent wrote: > I was wondering about id re-use. > > Assuming that ids that are returned to the idr db are re-used > what would the chance that a recently used id would end up > being used? > > Would that chance increase as ids are consumed and freed over > time? I've added something to deal with that in the fsinfo branch. I've given each mount object and superblock a supplementary 64-bit unique ID that's not likely to repeat before we're no longer around to have to worry about it. fsinfo() then allows you to retrieve them by path or by mount ID. So, yes, mnt_id and s_dev are not unique and may be reused very quickly, but I'm also providing uniquifiers that you can check. David