On Thu, Aug 26, 2021 at 06:43:44PM -0500, Eric Sandeen wrote:
> On 8/26/21 5:08 PM, Bill O'Donnell wrote:
> > On Thu, Aug 26, 2021 at 01:16:22PM -0500, Eric Sandeen wrote:
> > >
> > > On 8/26/21 1:09 PM, Darrick J. Wong wrote:
> > > > On Thu, Aug 26, 2021 at 12:30:12PM -0500, Bill O'Donnell wrote:
> > >
> > > > > @@ -1584,7 +1586,7 @@ xfs_fs_fill_super(
> > > > > if (xfs_has_crc(mp))
> > > > > sb->s_flags |= SB_I_VERSION;
> > > > > - if (xfs_has_dax_always(mp)) {
> > > > > + if (xfs_has_dax_always(mp) || xfs_has_dax_inode(mp)) {
> > > >
> > > > Er... can't this be done without burning another feature bit by:
> > > >
> > > > if (xfs_has_dax_always(mp) || (!xfs_has_dax_always(mp) &&
> > > > !xfs_has_dax_never(mp))) {
> > > > ...
> > > > xfs_warn(mp, "DAX IS EXPERIMENTAL");
> > > > }
> > >
> > > changing this conditional in this way will also fail dax=inode mounts on
> > > reflink-capable (i.e. default) filesystems, no?
> >
> > Correct. My original patch tests fine, and still handles the reflink and dax
> > incompatibility. The new suggested logic is problematic.
> > -Bill
>
> I think that both your proposed patch and Darrick's suggestion have this problem.
>
> "mount -o dax=inode" makes your new xfs_has_dax_inode(mp) true, and in that
> conditional, if the filesystem has reflink enabled, mount fails:
>
> # mkfs.xfs -f /dev/pmem0p1
> meta-data=/dev/pmem0p1 isize=512 agcount=4, agsize=4194304 blks
> = sectsz=4096 attr=2, projid32bit=1
> = crc=1 finobt=1, sparse=1, rmapbt=0
> = reflink=1 bigtime=0 inobtcount=0
> data = bsize=4096 blocks=16777216, imaxpct=25
> = sunit=0 swidth=0 blks
> naming =version 2 bsize=4096 ascii-ci=0, ftype=1
> log =internal log bsize=4096 blocks=8192, version=2
> = sectsz=4096 sunit=1 blks, lazy-count=1
> realtime =none extsz=4096 blocks=0, rtextents=0
>
> # mount -o dax=inode /dev/pmem0p1 /mnt/test
> mount: wrong fs type, bad option, bad superblock on /dev/pmem0p1,
> missing codepage or helper program, or other error
>
> In some cases useful info is found in syslog - try
> dmesg | tail or so.
>
> # dmesg | tail -n 2
> [ 192.691733] XFS (pmem0p1): DAX enabled. Warning: EXPERIMENTAL, use at your own risk
> [ 192.700300] XFS (pmem0p1): DAX and reflink cannot be used together!
>
So, the "DAX enabled" is a misnomer in this case. However the incompatibility of DAX and reflink is
reflected in the next message, and indeed the mount fails. Is it now a matter of fixing
the message output so as not to indicate "DAX enabled..."?
Thanks-
Bill
