From: "J. Bruce Fields" Subject: Re: writeable file with no mnt_want_write() Date: Mon, 7 Jul 2008 15:05:17 -0400 Message-ID: <20080707190517.GF14291@fieldses.org> References: <486CC466.6060504@panasas.com> <20080703203601.GE30918@fieldses.org> <486E18C3.1040703@panasas.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: NFS list To: Benny Halevy Return-path: Received: from mail.fieldses.org ([66.93.2.214]:49791 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754679AbYGGTFT (ORCPT ); Mon, 7 Jul 2008 15:05:19 -0400 In-Reply-To: <486E18C3.1040703@panasas.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Jul 04, 2008 at 03:34:11PM +0300, Benny Halevy wrote: > On Jul. 03, 2008, 23:36 +0300, "J. Bruce Fields" wrote: > > We're just trying to enforce rfc 3530 14.2.19: > > OK. I see. > Thanks for explaining! > It is a bit mind boggling, maybe adding some comments explaining > why the bitmap is needed would help... Where do you think you would have looked for a comment? I figured just before the helper functions here was one obvious place. --b. commit 4f83aa302f8f8b42397c6d3703d670f0588c03ec Author: J. Bruce Fields Date: Mon Jul 7 15:02:02 2008 -0400 nfsd: document open share bit tracking It's not immediately obvious from the code why we're doing this. Signed-off-by: J. Bruce Fields Cc: Benny Halevy diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index eca8aaa..c29b6ed 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -1173,6 +1173,24 @@ static inline int deny_valid(u32 x) return x <= NFS4_SHARE_DENY_BOTH; } +/* + * We store the NONE, READ, WRITE, and BOTH bits separately in the + * st_{access,deny}_bmap field of the stateid, in order to track not + * only what share bits are currently in force, but also what + * combinations of share bits previous opens have used. This allows us + * to enforce the recommendation of rfc 3530 14.2.19 that the server + * return an error if the client attempt to downgrade to a combination + * of share bits not explicable by closing some of its previous opens. + * + * XXX: This enforcement is actually incomplete, since we don't keep + * track of access/deny bit combinations; so, e.g., we allow: + * + * OPEN allow read, deny write + * OPEN allow both, deny none + * DOWNGRADE allow read, deny none + * + * which we should reject. + */ static void set_access(unsigned int *access, unsigned long bmap) { int i;