On Wed, Mar 24, 2021 at 11:17:59AM -0700, Darrick J. Wong wrote:

On Wed, Mar 24, 2021 at 03:21:16PM +0100, Christoph Hellwig wrote:

quoted

The legacy DMAPI fields were never set by upstream Linux XFS, and have no
way to be read using the kernel APIs.  So instead of bloating the in-core
inode for them just copy them from the on-disk inode into the log when
logging the inode.  The only caveat is that we need to make sure to zero
the fields for newly read or deleted inodes, which is solved using a new
flag in the inode.

How long ago /did/ non-upstream XFS have DMAPI support?  Does it still
have it now?  What's the cost of zeroing the fields?

(Really what I'm saying is that I have so little clue of what dmevmask
and dmstate do that I don't really know what Magic Smoke comes out if
these fields get zeroed by an upstream kernel.)

SuSE is shipping SGI patches for it in SLES12, their second newest
release. Which is still supported AFAIK.