From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751713AbcKQUAa (ORCPT ); Thu, 17 Nov 2016 15:00:30 -0500 Received: from fieldses.org ([173.255.197.46]:50322 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750939AbcKQUA1 (ORCPT ); Thu, 17 Nov 2016 15:00:27 -0500 Date: Thu, 17 Nov 2016 15:00:26 -0500 To: David Howells Cc: One Thousand Gnomes , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH 0/4] Enhanced file stat system call Message-ID: <20161117200026.GE20937@fieldses.org> References: <20161117143904.4ae757b4@lxorguk.ukuu.org.uk> <147938969703.13574.10295364502230379833.stgit@warthog.procyon.org.uk> <15516.1479401145@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <15516.1479401145@warthog.procyon.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) From: bfields@fieldses.org (J. Bruce Fields) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 17, 2016 at 04:45:45PM +0000, David Howells wrote: > One Thousand Gnomes wrote: > > > > (2) Lightweight stat (AT_STATX_DONT_SYNC): Ask for just those details of > > > interest, and allow a network fs to approximate anything not of > > > interest, without going to the server. > > > > > > (3) Heavyweight stat (AT_STATX_FORCE_SYNC): Force a network fs to flush > > > buffers and go to the server, even if it thinks its cached attributes > > > are up to date. > > > > That seems an odd way to do it. Wouldn't it be cleaner and more flexible > > to give a timestamp of the oldest time you consider acceptable (and > > obviously passing 0 indicates whatever you have) > > Perhaps, though adding 6-argument syscalls is apparently frowned upon. > > > > Note that no lstat() equivalent is required as that can be implemented > > > through statx() with atflag == 0. There is also no fstat() equivalent as > > > that can be implemented through statx() with filename == NULL and the > > > relevant fd passed as dfd. > > > > and dfd + a name gives you fstatat() ? > > Yes. > > > The cover note could be clearer on this. > > Fixed. > > > Should the fields really be split the way they are for times rather than > > a struct for each one so you can write code generically to handle one of > > those rather than having to have a 4 way switch statement all the time. > > It depends. Doing so leaves 16 bytes of hole in the structure. I could > ameliorate the wastage by using a union to overlay useful fields in the gaps, > but that's pretty icky and might be compiler dependent. > > > Another attribute that would be nice (but migt need some trivial device > > layer tweaking) would be STATX_ATTR_VOLATILE for filesystems that will > > probably evaporate on a reboot. That's useful information for tools like > > installers and also for sanity checking things like backup paths. > > There's a FILE_ATTRIBUTE_TEMPORARY that I could map for windows filesystems > that could be used with this. > > > Remote needs to have clear semantics: is ext4fs over nbd 'remote' for > > example ? > > Hmmm... Interesting question. Probably should. But you could be insane and > RAID an nbd and a local disk. Further, does NFS over a loopback device to > nfsd on the same machine qualify as root? What if that's exposing a local fs > on NBD? Perhaps I should drop 'REMOTE' for now. It sounds like something > that a GUI filemanager might find interesting, though. Sorry, I haven't been paying attention, just popping up for this, but: "shared" might be a more useful term than "remote". A filesystem that may be mounted from more than one system is "shared". Caching performance and semantics of such a filesystem are more complicated since the filesystem may change out from under us. This is what makes e.g. the lightweight/heavyweight stat difference more interesting in the shared case. The filesystem should be able to make that shared/unshared distinction without knowledge of the storage it's sitting on top of. Answering your questions by that criterion: - ext4/nbd: not shared - nfs/lo: shared But, it's fine with me to drop any features for now as long as we can always add them later. --b.