Re: [PATCH 1/6] Btrfs: add mount option for dax

[Dave Chinner <david@fromorbit.com>]

On Fri, Dec 09, 2016 at 10:41:34AM -0800, Liu Bo wrote:
> On Fri, Dec 09, 2016 at 03:47:20PM +1100, Dave Chinner wrote:
> > On Wed, Dec 07, 2016 at 01:45:05PM -0800, Liu Bo wrote:
> > > Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> > > ---
> > >  fs/btrfs/ctree.h |  1 +
> > >  fs/btrfs/super.c | 40 +++++++++++++++++++++++++++++++++++++++-
> > >  2 files changed, 40 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> > > index 0b8ce2b..e54c6e6 100644
> > > --- a/fs/btrfs/ctree.h
> > > +++ b/fs/btrfs/ctree.h
> > > @@ -1317,6 +1317,7 @@ static inline u32 BTRFS_MAX_XATTR_SIZE(const struct btrfs_root *root)
> > >  #define BTRFS_MOUNT_FRAGMENT_METADATA	(1 << 25)
> > >  #define BTRFS_MOUNT_FREE_SPACE_TREE	(1 << 26)
> > >  #define BTRFS_MOUNT_NOLOGREPLAY		(1 << 27)
> > > +#define BTRFS_MOUNT_DAX		(1 << 28)
> > >  
> > >  #define BTRFS_DEFAULT_COMMIT_INTERVAL	(30)
> > >  #define BTRFS_DEFAULT_MAX_INLINE	(2048)
> > > diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> > > index 74ed5aa..9b18f3d 100644
> > > --- a/fs/btrfs/super.c
> > > +++ b/fs/btrfs/super.c
> > > @@ -323,7 +323,7 @@ enum {
> > >  	Opt_commit_interval, Opt_barrier, Opt_nodefrag, Opt_nodiscard,
> > >  	Opt_noenospc_debug, Opt_noflushoncommit, Opt_acl, Opt_datacow,
> > >  	Opt_datasum, Opt_treelog, Opt_noinode_cache, Opt_usebackuproot,
> > > -	Opt_nologreplay, Opt_norecovery,
> > > +	Opt_nologreplay, Opt_norecovery, Opt_dax,
> > 
> > Can we please not create more filesystems with a DAX mount option?
> > This was only even an enabler, and not meant to be a permanent
> > thing. The permanent functionality for DAX is supposed to be
> > per-inode inheritable DAX flags - not mount options - so that
> > applications can choose on a per file basis to enable/disable DAX
> > access as they see fit.
> > 
> > This also enables the filesystem to reject the attempt to turn on
> > DAX if the set of contexts for the file are not DAX compatible....
> 
> Sounds good, I'll try to update it to use inode DAX flag directly.

xfs_io already has chattr/lsattr support (+/-x) for the FS_XFLAG_DAX
flag in FS_IOC_FS{GS}ETXATTR, and you can have a look at the XFS
code in xfs_ioctl.c for the operations that are needed to
dynamically change the S_DAX flag on an inode (e.g
xfs_ioctl_setattr_dax_invalidate())

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com