On Fri, Aug 27, 2021 at 09:18:32AM -0500, Eric Sandeen wrote:
> On 8/27/21 9:03 AM, Bill O'Donnell wrote:
> > 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..."?
>
> The mount should not fail, and it does not fail prior to your change.
>
> In the past, we did not allow any mixing of a reflink-capable
> filesystem with dax in any way. Now, with per-inode dax, dax-enabled inodes and
> reflink-enabled inodes can exist on the same filesystem, you just cannot have an
> inode which is both dax-enabled and reflinked at the same time.
Ah. I missed that nuance. I had thought the incompatibility was
absolute. :/
The manpage for mkfs.xfs may need updating for the inode mode
(unless mine is old):
----------------snip------------------
"Note: the filesystem DAX mount option ( -o dax ) is incom‐
patible with reflink-enabled XFS filesystems. To use
filesystem DAX with XFS, specify the -m reflink=0 option to
mkfs.xfs to disable the reflink feature."
-------------------------------------
Thanks-
Bill
