From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aurelien Degremont Subject: Re: NFS superblock sharing implies mount flags bug Date: Mon, 20 Mar 2006 14:20:05 +0100 Message-ID: <441EAC05.7020903@cea.fr> References: <200603151038.LAA21392@styx.bruyeres.cea.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, nfs@lists.sourceforge.net, Jacques-Charles Lafoucriere Return-path: To: trond.myklebust@fys.uio.no, viro@zeniv.linux.org.uk In-Reply-To: <200603151038.LAA21392@styx.bruyeres.cea.fr> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Nobody is interested by this issue ? It could be easily reproduced. All recent versions are concerned. Aurelien Aurelien Degremont wrote: > Hello > > I'm facing incorrect using of mount flags when dealing with NFS mounts > and I think it could be seen as a bug. > > The error occurs when mounting the same NFS export many times, on the > same machine but *with different mount flags*, particularly concerning > RO/RW flags. > > As the NFS client code re-uses superblocks when it detects that it is > the same export (same server/same port/same exported directory) and that > the read-only flag is managed as a per-superblock flag, if a NFS exports > is mounted a second time, the superblock of the first mount is re-used > and the specified mount flag is ignored. > > # mount foo:/bar /bar_ro -o ro > # mount foo:/bar /bar_rw -o rw > $ touch /bar_rw/bar > touch: cannot touch `/bar_rw/bar': Read-only file system > > Ideally, the best solution to fix this is to move the RDONLY flag from > its per-superblock basis to a per-mountpoint (vfsmount) basis. I do not > know is there is a something that prevent that except that this implies > many changes as many codes do not use macros but access s_flags directly. > > It seems quite clear that the superblock sharing couldn't be changed (to > avoid incoherency, inode aliasing and so on...) ? > > Do you have a (better) solution ? > I can help if needed. > > > Cordially > -- Aurelien Degremont CEA/DAM - DIF/DSSI/SISR