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

[Liu Bo <bo.li.liu@oracle.com>]

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.

Thanks,

-liubo