From: Dave Chinner Subject: Re: [PATCH v6 3/3] xfs: reject removal of realtime flag when datadev doesn't support DAX Date: Sun, 18 Feb 2018 11:23:17 +1100 Message-ID: <20180218002317.GU7000@dastard> References: <151880058592.43131.558230052922233871.stgit@djiang5-desk3.ch.intel.com> <151880066614.43131.15847174332875373188.stgit@djiang5-desk3.ch.intel.com> <20180216172247.GS5217@magnolia> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dave Jiang , linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org, ross.zwisler@linux.intel.com, linux-ext4@vger.kernel.org, dan.j.williams@intel.com To: "Darrick J. Wong" Return-path: Received: from ipmail06.adl6.internode.on.net ([150.101.137.145]:47976 "EHLO ipmail06.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751083AbeBRAXV (ORCPT ); Sat, 17 Feb 2018 19:23:21 -0500 Content-Disposition: inline In-Reply-To: <20180216172247.GS5217@magnolia> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Feb 16, 2018 at 09:22:47AM -0800, Darrick J. Wong wrote: > On Fri, Feb 16, 2018 at 10:04:26AM -0700, Dave Jiang wrote: > > In a situation where the rt_dev is DAX and data_dev is not DAX, if the user > > requests to remove the realtime flag via ioctl we can no longer support DAX > > for that file. Dynamic changing of S_DAX on the inode is not supported due > > to various complications in the existing implementation. Therefore until we > > address the dynamic S_DAX change issues, we must disallow realtime flag > > being removed. > > > > Signed-off-by: Dave Jiang > > Reviewed-by: Christoph Hellwig > > --- > > fs/xfs/xfs_ioctl.c | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c > > index 2c70a0a4f59f..edd97d527fe8 100644 > > --- a/fs/xfs/xfs_ioctl.c > > +++ b/fs/xfs/xfs_ioctl.c > > @@ -1030,6 +1030,20 @@ xfs_ioctl_setattr_xflags( > > { > > struct xfs_mount *mp = ip->i_mount; > > uint64_t di_flags2; > > + struct inode *inode = VFS_I(ip); > > + struct super_block *sb = inode->i_sb; > > + > > + /* > > + * In the case that the inode is realtime, and we are trying to remove > > + * the realtime flag, and the rtdev supports DAX but the datadev does > > + * not support DAX, we can't allow the realtime flag to be removed > > + * since we do not support dynamic S_DAX flag removal yet. > > + */ > > + if (XFS_IS_REALTIME_INODE(ip) && > > + !(fa->fsx_xflags & FS_XFLAG_REALTIME) && > > + bdev_dax_supported(mp->m_rtdev_targp->bt_bdev, sb->s_blocksize) && > > + !bdev_dax_supported(mp->m_ddev_targp->bt_bdev, sb->s_blocksize)) > > What happens here if we have a non-rt file that we're trying to turn > into an rt file and the data dev supports dax but not the rt dev? > > Changing the rt flag is only supported on files with no data blocks (no > extents, no delalloc blocks), so why can't we remove S_DAX from an empty > file? There aren't any memory mappings or page cache to get in the way, > correct? File size can be non-zero, so you can have DAX read-over-hole mappings present. I simply don't think it's safe to remove/add S_DAX flags via ioctls right now. If we have a DAX capable rtdev, then the only way we should allow rtdev+dax to be used right now is via the RT inherit bit on the dir that creates files in the rtdev right from the start. i.e. we can't set/remove the RT inode flag on an inode via ioctl if rtdev+dax is enabled until the whole dynamic S_DAX inode flag thing is resolved. Cheers, Dave. -- Dave Chinner david@fromorbit.com