On 10/28/21 8:45 AM, Dan Williams wrote:

The /sys/class/dax compatibility option has shipped in the kernel for 4
years now which should be sufficient time for tools to abandon the old
ABI in favor of the /sys/bus/dax device-model. Delete it now and see if
anyone screams.

Since this compatibility option shipped there has been more reports of
users being surprised by the compat ABI than surprised by the "new", so
the compat infrastructure has outlived its usefulness. Recall that
/sys/bus/dax device-model is required for the dax kmem driver which
allows PMEM to be used as "System RAM".

Cc: Ira Weiny <redacted>
Cc: Dave Jiang <dave.jiang@intel.com>

The compat module has bitten me more than once, and confused more than
one end user who tried to use the kmem facility.  It's definitely a
liability:

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>