On 8/27/21 10:49 AM, Darrick J. Wong wrote:

On Fri, Aug 27, 2021 at 10:39:18AM -0500, Eric Sandeen wrote:

quoted

Now that we have the tristate dax mount options, it is possible
to enable DAX mode for non-reflinked files on a reflink-capable
filesystem.  Clarify this in the mkfs.xfs manpage.

Reported-by: Bill O'Donnell <redacted>
Signed-off-by: Eric Sandeen <redacted>
---

diff --git a/man/man8/mkfs.xfs.8 b/man/man8/mkfs.xfs.8
index a7f70285..84ac50e8 100644
--- a/man/man8/mkfs.xfs.8
+++ b/man/man8/mkfs.xfs.8

@@ -316,12 +316,20 @@ option set. When the option
  is used, the reference count btree feature is not supported and reflink is
  disabled.
  .IP
-Note: the filesystem DAX mount option (
+Note: the filesystem-wide DAX mount options (
  .B \-o dax
-) is incompatible with
-reflink-enabled XFS filesystems.  To use filesystem DAX with XFS, specify the
+and
+.B \-o dax=always
+) are incompatible with
+reflink-enabled XFS filesystems.  To use filesystem-wide DAX with XFS, specify the
  .B \-m reflink=0
  option to mkfs.xfs to disable the reflink feature.
+Alternatey, use the

"Alternately..."

"Alternatively,"

quoted

+.B \-o dax=inode
+mount option to selectively enable DAX mode on non-reflinked files.

/me wonders if this is dangerously close to wading into the muck that is
"Use dax=inode or even no dax option at all, then make sure nobody
shares your file's data blocks to set the DAX fsxattr flag on the file,
and /then/ you can have DAX."

Perhaps I should drop most of it, and just wave hands vaguely at xfs.5?

-Eric