From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6489F762DE; Tue, 28 May 2024 07:15:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716880556; cv=none; b=i57M2O2MEZofpqss8r2EHSgzTAai5iUapzFVwf0L0ooKOwLBqjee7DO5YoBuBxGQbiJAQ7wwrrCySNmrEe8iglR/1bGMFNBCAoYOIGA2k/AFGGuy52+2oenlMcPzEnclr75NTRn2BnSq93QOs83LgJ+mcDLq7IdWcHit+jwkO3Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716880556; c=relaxed/simple; bh=MLD9H2Czeuk8yzIl1o8T8vYs2svQSfY1C3nOel6q2Q8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=O1oaacQnHXy1muV+NMQ2jJgVyjQv6pvvP3y6cSHGJ4forfo3vvlkNXntmh+kNlfLPk97LZaLyiwozZ4lxpwXWBx8RvxDVxXwkQiHnTd9RyhTO9Wypl88BaltBD/E3K7D3ycyPTMrhoUVgeiA5ew65msLZuoniZuTHKJqmE4VgXs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=ZeEaFy8H; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ZeEaFy8H" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=c56LmE5EVD7j+b/usANfOmh+EBtk5ZiTU/F1vZzSWfI=; b=ZeEaFy8HdyEAO9fdeR/nxeNUJF ogdOH5XkKv1kGbNB3Eizu2B5Y8ZeDo9IUNuf4osGALsJAbbuijUbR2lsZOW+bRTPLv8oWDpGF0l22 9pprWxzdsXSkGEgwz8qwjKMiFJYe/K6DGUZRlcX1L1EqDVbQEbMNXCxparCu32Z3Zw4RHX6keIX6z KSi61oaTs02/u0nuzM5DbLrSd4SQ0y4z7v0pOgz5MufyfIYLx+y116pX+FqgDbeD07DP9Hje3rKbh H7Y0acQIZ2yCIMAYquzTUBNbj55FryZzAjnCKshjlCyBl1HdJB0fCtAY6StAy+Q0a5GYsbAQzDIeL gbIk1acQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sBr3o-0000000HILb-231F; Tue, 28 May 2024 07:15:52 +0000 Date: Tue, 28 May 2024 00:15:52 -0700 From: "hch@infradead.org" To: Christian Brauner Cc: "hch@infradead.org" , Trond Myklebust , "jack@suse.cz" , "chuck.lever@oracle.com" , "linux-api@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "alex.aring@gmail.com" , "cyphar@cyphar.com" , "viro@zeniv.linux.org.uk" , "jlayton@kernel.org" , "amir73il@gmail.com" , "linux-nfs@vger.kernel.org" Subject: Re: [PATCH RFC v2] fhandle: expose u64 mount id to name_to_handle_at(2) Message-ID: References: <20240523-exportfs-u64-mount-id-v2-1-f9f959f17eb1@cyphar.com> <30137c868039a3ae17f4ae74d07383099bfa4db8.camel@hammerspace.com> <86065f6a4f3d2f3d78f39e7a276a2d6e25bfbc9d.camel@hammerspace.com> <20240528-fraglich-abmildern-cca211d1791c@brauner> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240528-fraglich-abmildern-cca211d1791c@brauner> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Tue, May 28, 2024 at 09:12:33AM +0200, Christian Brauner wrote: > It's also used by userspace for uniquely identifying cgroups via handles > as cgroups and - even without open_by_handle_at() - to check whether a > file is still valid. > > And again a 64bit mount is is a simple way to race-free go to whatever > superblock uuid you want. They cannot be recycled and are unique for the > lifetime of the system. And then break when you reboot. Which you might not care about for cgroups, but which is really bad for the concept of a file handle. See one of my other replies for a proposed interface that is just as easy to use for userspace, a little more complex in the kernel but safe for it. I'd much prefer that over using ay kind of "mount ID" which doesn't fit into the file handle concept at all.