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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 BB359C43218 for ; Sat, 27 Apr 2019 20:16:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 78A082077B for ; Sat, 27 Apr 2019 20:16:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="YTdcDCKF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726198AbfD0UQz (ORCPT ); Sat, 27 Apr 2019 16:16:55 -0400 Received: from mail-yw1-f68.google.com ([209.85.161.68]:43064 "EHLO mail-yw1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726088AbfD0UQz (ORCPT ); Sat, 27 Apr 2019 16:16:55 -0400 Received: by mail-yw1-f68.google.com with SMTP id w196so2378189ywd.10; Sat, 27 Apr 2019 13:16:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=X7nIKq30gmNteOhuVTtXwzawEY+p5Z4tJsssF9WMYtM=; b=YTdcDCKFP8Wusps0xQ2BYOOkrKX2CrNRaEUAoW3pFyzoE7aVcc7edu59oCKcG24nJ+ t/Me5myN59chQFA34FhFOmQG1fmH2ZOk3fofbvgNKEyfaxIvAbNrYBj6cWNXoAUlfTdU GLEsxehnNKqlNZKGcakxWNaPTWq+XZkgb6nFap4fcoBc3bN3Odds9I+xneLqT9cnmcq5 Glw9qWjpfwvK1tfe4ib6jpxC0U3l8BlRPcjo7OaDrS0qH5diX6o86iZAbSaLPRGsBlnR OlLgPppHxBGwjqbWnEeA5Bx7lZcjiD93pss3FBIie8vu6FpVnjFO9uuib+AigfiW1t2H yroQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=X7nIKq30gmNteOhuVTtXwzawEY+p5Z4tJsssF9WMYtM=; b=YyPMC2DOdHXFw9pkNVN+IYEYCpoYickWd+FWIhj15QS4cYyTuww+ww+enRldKZaOJF lJ++S6FppRVyWoIyUAQE4rJxvjE6lWHjT65C91YZgGfdIlSryqNVlnBCX6nF4gb9xYW7 ZPd/uCgMvcHIrvz0sV7mXawmbeb5WAZlDBE2Z1rPaQMKqazMsyg1MrWiuGlmQ2IuZGh+ 7BFmj2slqO4BjiLGDONmrACs5NTCBLqIciQvOVZJ0idr4gZUse7yGyESvJrX/HfmKT5/ pz1sFUJfbWaDG0zhXAXmmEsUWMxTnzD4RSgoD4E4AaAGjO0CGYNkFCuc7iLilQK7RO+A BiiQ== X-Gm-Message-State: APjAAAWUNzP/KV+qq1XgAtNHymO3NwfGpoTbuN5VhyCSFSKK51aMeONK r97Gb15//6c1VGtQv89TB+Uq4MxYj8qhGy4ZrTQ= X-Google-Smtp-Source: APXvYqyMiv4Q75Gsfnaru5UqCRjb6WzLYfjr5aY84foN+Agu0n9ANzxebHWhVCwNu6rZLZknxtXrOi9aQoQvPkCGksc= X-Received: by 2002:a81:7c4:: with SMTP id 187mr44913328ywh.176.1556396214239; Sat, 27 Apr 2019 13:16:54 -0700 (PDT) MIME-Version: 1.0 References: <379106947f859bdf5db4c6f9c4ab8c44f7423c08.camel@kernel.org> <930108f76b89c93b2f1847003d9e060f09ba1a17.camel@kernel.org> <20190426140023.GB25827@fieldses.org> <20190426145006.GD25827@fieldses.org> In-Reply-To: From: Amir Goldstein Date: Sat, 27 Apr 2019 16:16:42 -0400 Message-ID: Subject: Re: Better interop for NFS/SMB file share mode/reservation To: Jeff Layton Cc: "J. Bruce Fields" , Volker.Lendecke@sernet.de, samba-technical , linux-fsdevel , Linux NFS Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org [adding back samba/nfs and fsdevel] On Fri, Apr 26, 2019 at 6:22 PM Jeff Layton wrote: > > On Fri, 2019-04-26 at 10:50 -0400, J. Bruce Fields wrote: > > On Fri, Apr 26, 2019 at 04:11:00PM +0200, Amir Goldstein wrote: > > > On Fri, Apr 26, 2019, 4:00 PM J. Bruce Fields wrote: > > > > > > > On Fri, Apr 26, 2019 at 03:50:46PM +0200, Amir Goldstein wrote: > > > > > On Fri, Feb 8, 2019, 5:03 PM Jeff Layton wrote: > > > > > > Share/deny open semantics are pretty similar across NFS and SMB (by > > > > > > design, really). If you intend to solve that use-case, what you really > > > > > > want is whole-file, shared/exclusive locks that are set atomically with > > > > > > the open call. O_EXLOCK and O_SHLOCK seem like a reasonable fit there. > > > > > > > > > > > > Then you could have SMB and NFS servers set these flags when opening > > > > > > files, and deal with the occasional denial at open time. Other > > > > > > applications won't be aware of them of course, but that's probably fine > > > > > > for most use-cases where you want this sort of protocol interop. > > > > > > > > > > Sorry for posting off list. Airport emails... > > > > > I looked at implemeting O_EXLOCK and O_SHLOCK and it looks doable. > > > > > > > > > > I was wondering if there is an inherent reason not to allow an exclusive > > > > > lock on a file that is open read-only. > > > > > > > > > > Samba seems to need it and currently flock and ofd locks won't allow it. > > > > > Do you thing it will be ok to allow it with O_EXLOCK? > > > > > > > > Somebody could deny everyone access to a shared resource that everyone > > > > needs to make progress, like /etc/passwd or a shared library. > > > > > > > > Have you looked at Pavel Shilovsky's O_DENY patches? He had the feature > > > > off by default, with a mount option provided to turn it on. > > > > > > > > > > O_EXLOCK is advisory. It only aquired flock or ofd lock atomically with > > > open. > > > > Whoops, got it. > > > > Is that really adequate for open share locks, though? > > > > I assumed that Windows apps depend on the assumption that they're > > mandatory. So e.g. if you can get a DENY_READ open on a shared library > > then you know you can update it without the risk of making someone else > > crash. > > > > I think this is (slightly) better than doing it internally like we do > today and would give you coherent locking between NFS and SMB. Other > applications wouldn't see them, but for a NAS-style deployment, that's > probably ok. > We can do a little bit better. We can make sure that O_DENY_WRITE (named for convenience) fails if file is currently open for write by anyone and similarly for O_DENY_READ. But if we cannot deny future non-cooperative opens what's the point?.... > Any open by samba or nfsd would need to start setting O_SHLOCK, and deny > mode opens would have to set O_EXLOCK. We would actually need 2 per > inode though (one for read and one for write). > ...the point is that O_DENY_NONE does not need to be implemented with a new type of lock object (O_WR_SHLOCK) its enough that it checks there are no relevant exclusive locks and the then inode->i_writecount and inode->i_readcount already provide enough context to cooperate with O_DENY_WRITE and O_DENY_READ. I need to see if incrementing inode->i_readcount on O_RDWR opens is possible (right now it only counts O_RDONLY opens). > I think these should probably be in their own "namespace" too. They > could use the same semantics as flock, but should sit on their own list > in file_lock_context. > I would much rather that they didn't. The reason is that new open flags are a backward compat problem. The way I want to solve it is this API: // On new kernel this will acquire OFD F_WRLCK atomically... fd = open(..., O_RDWR | O_EXLOCK); // ...check if it did acquire OFD lock fcntl(fd, F_OFD_GETLK, ...); We'd need at least one new l_type F_EX_RDLCK and maybe also a new semantic F_EX_RDWRLCK, although similar in conflicts to F_WRLCK it can be acquired without FMODE_WRITE. Though I personally thing we can do without it if the only way to acquire F_WRLCK on readonly file is via new open flag. > That said, we could also look at a vfs-level mount option that would > make the kernel enforce these for any opener. That could also be useful, > and shouldn't be too hard to implement. Maybe even make it a vfsmount- > level option (like -o ro is). > Yeh, I am humbly going to leave this struggle to someone else. Not important enough IMO and completely independent effort to the advisory atomic open&lock API. > If you're denied, what error should you get back when you try to open > it? It should be something distinct. We may even want to add new error > codes for this. IMO EBUSY does the job. Its distinct because open is not expected to return EBUSY for regular files/dirs and when open is expected to return EBUSY for blockdev its for the exact same use case (i.e. exclusive write open is acquired by userspace tools). Thanks, Amir.