On Thu, Sep 20, 2018 at 01:17:02PM -0700, Darrick J. Wong wrote: > On Thu, Sep 20, 2018 at 04:42:20PM +0200, Christoph Hellwig wrote: > > When the (debug-only) always_cow module parameter is set, we will always > > write out place, even if the file is not reflinked. In addition to being > > a useful debug aid this prepares for modes where we must always write > > out of place. An example for that is the upcoming support for atomic > > overwrites. .... > > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c > > index b25ea7a3a0e7..a893f6d65ff0 100644 > > --- a/fs/xfs/xfs_reflink.c > > +++ b/fs/xfs/xfs_reflink.c > > @@ -129,6 +129,11 @@ > > * ioend, the better. > > */ > > > > +#ifdef DEBUG > > +bool xfs_always_cow; > > +module_param_named(always_cow, xfs_always_cow, bool, 0644); > > +#endif > > I would have expected this to end up in /proc/sys/fs/xfs/always_cow > along with all the other behavior knobs, but I guess this is a debugging > thing...? sys/fs/xfs/debug/always_cow is the place for this if it is truly a global debug option. However, that's probably not the best way to enable this sort of debug for people with XFS root filesystems trying to test XFS filesystems. I suspect it should be a per-mount configuration (i.e. /sys/fs/xfs/<dev>/debug/always_cow) However, this mode of operation seems like it is going to form the basis of other per-filesystem features, so it would be good to know how/if those features make use of this always_cow mode or are controlled by some other set of knobs first. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
