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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 5D870C433E0 for ; Wed, 12 Aug 2020 15:08:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 40EB320781 for ; Wed, 12 Aug 2020 15:08:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726627AbgHLPIg (ORCPT ); Wed, 12 Aug 2020 11:08:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726477AbgHLPIX (ORCPT ); Wed, 12 Aug 2020 11:08:23 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 05E8FC061383; Wed, 12 Aug 2020 08:08:23 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k5sMJ-00E8Uk-5O; Wed, 12 Aug 2020 15:08:07 +0000 Date: Wed, 12 Aug 2020 16:08:07 +0100 From: Al Viro To: Miklos Szeredi Cc: Linus Torvalds , Jann Horn , Casey Schaufler , Andy Lutomirski , linux-fsdevel , David Howells , Karel Zak , Jeff Layton , Miklos Szeredi , Nicolas Dichtel , Christian Brauner , Lennart Poettering , Linux API , Ian Kent , LSM , Linux Kernel Mailing List Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information) Message-ID: <20200812150807.GR1236603@ZenIV.linux.org.uk> References: <5C8E0FA8-274E-4B56-9B5A-88E768D01F3A@amacapital.net> <20200812143957.GQ1236603@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 12, 2020 at 04:46:20PM +0200, Miklos Szeredi wrote: > > "Can those suckers be passed to > > ...at() as starting points? > > No. Lovely. And what of fchdir() to those? Are they all non-directories? Because the starting point of ...at() can be simulated that way... > > Can they be bound in namespace? > > No. > > > Can something be bound *on* them? > > No. > > > What do they have for inodes > > and what maintains their inumbers (and st_dev, while we are at > > it)? > > Irrelevant. Can be some anon dev + shared inode. > > The only attribute of an attribute that I can think of that makes > sense would be st_size, but even that is probably unimportant. > > > Can _they_ have secondaries like that (sensu Swift)? > > Reference? http://www.online-literature.com/swift/3515/ So, naturalists observe, a flea Has smaller fleas that on him prey; And these have smaller still to bite 'em, And so proceed ad infinitum. of course ;-) IOW, can the things in those trees have secondary trees on them, etc.? Not "will they have it in your originally intended use?" - "do we need the architecture of the entire thing to be capable to deal with that?" > > Is that a flat space, or can they be directories?" > > Yes it has a directory tree. But you can't mkdir, rename, link, > symlink, etc on anything in there. That kills the "shared inode" part - you'll get deadlocks from hell that way. "Can't mkdir" doesn't save you from that. BTW, what of unlink()? If the tree shape is not a hardwired constant, you get to decide how it's initially populated... Next: what will that tree be attached to? As in, "what's the parent of its root"? And while we are at it, what will be the struct mount used with those - same as the original file, something different attached to it, something created on the fly for each pathwalk and lazy-umounted? And see above re fchdir() - if they can be directories, it's very much in the game.