dax: Kill DEV_DAX_PMEM_COMPAT

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".

The following projects were known to have a dependency on /sys/class/dax
and have dropped their dependency as of the listed version:

- ndctl (including libndctl, daxctl, and libdaxctl): v64+
- fio: v3.13+
- pmdk: v1.5.2+

As further evidence this option is no longer needed some distributions
have already stopped enabling CONFIG_DEV_DAX_PMEM_COMPAT.

Cc: Ira Weiny <[email protected]>
Cc: Dave Jiang <[email protected]>
Reported-by: Vishal Verma <[email protected]>
Acked-by: Dave Hansen <[email protected]>
Reviewed-by: Jane Chu <[email protected]>
Link: https://lore.kernel.org/r/163701116195.3784476.726128179293466337.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <[email protected]>

Author: djbw

Documentation/ABI/obsolete/sysfs-class-dax

@@ -70,13 +70,4 @@ config DEV_DAX_KMEM
 
 	  Say N if unsure.
 
-config DEV_DAX_PMEM_COMPAT
-	tristate "PMEM DAX: support the deprecated /sys/class/dax interface"
-	depends on m && DEV_DAX_PMEM=m
-	default DEV_DAX_PMEM
-	help
-	  Older versions of the libdaxctl library expect to find all
-	  device-dax instances under /sys/class/dax. If libdaxctl in
-	  your distribution is older than v58 say M, otherwise say N.
-
 endif

drivers/dax/Kconfig

@@ -2,10 +2,11 @@
 obj-$(CONFIG_DAX) += dax.o
 obj-$(CONFIG_DEV_DAX) += device_dax.o
 obj-$(CONFIG_DEV_DAX_KMEM) += kmem.o
+obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem.o
 
 dax-y := super.o
 dax-y += bus.o
 device_dax-y := device.o
+dax_pmem-y := pmem.o
 
-obj-y += pmem/
 obj-y += hmem/

drivers/dax/Makefile

@@ -10,8 +10,6 @@
 #include "dax-private.h"
 #include "bus.h"
 
-static struct class *dax_class;
-
 static DEFINE_MUTEX(dax_bus_lock);
 
 #define DAX_NAME_LEN 30
@@ -1343,10 +1341,7 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
 
 	inode = dax_inode(dax_dev);
 	dev->devt = inode->i_rdev;
-	if (data->subsys == DEV_DAX_BUS)
-		dev->bus = &dax_bus_type;
-	else
-		dev->class = dax_class;
+	dev->bus = &dax_bus_type;
 	dev->parent = parent;
 	dev->type = &dev_dax_type;
 
@@ -1445,22 +1440,10 @@ EXPORT_SYMBOL_GPL(dax_driver_unregister);
 
 int __init dax_bus_init(void)
 {
-	int rc;
-
-	if (IS_ENABLED(CONFIG_DEV_DAX_PMEM_COMPAT)) {
-		dax_class = class_create(THIS_MODULE, "dax");
-		if (IS_ERR(dax_class))
-			return PTR_ERR(dax_class);
-	}
-
-	rc = bus_register(&dax_bus_type);
-	if (rc)
-		class_destroy(dax_class);
-	return rc;
+	return bus_register(&dax_bus_type);
 }
 
 void __exit dax_bus_exit(void)
 {
 	bus_unregister(&dax_bus_type);
-	class_destroy(dax_class);
 }

drivers/dax/bus.c

@@ -16,24 +16,15 @@ struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 		struct range *range, int target_node, unsigned int align,
 		unsigned long flags);
 
-enum dev_dax_subsys {
-	DEV_DAX_BUS = 0, /* zeroed dev_dax_data picks this by default */
-	DEV_DAX_CLASS,
-};
-
 struct dev_dax_data {
 	struct dax_region *dax_region;
 	struct dev_pagemap *pgmap;
-	enum dev_dax_subsys subsys;
 	resource_size_t size;
 	int id;
 };
 
 struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data);
 
-/* to be deleted when DEV_DAX_CLASS is removed */
-struct dev_dax *__dax_pmem_probe(struct device *dev, enum dev_dax_subsys subsys);
-
 struct dax_device_driver {
 	struct device_driver drv;
 	struct list_head ids;
@@ -49,10 +40,6 @@ int __dax_driver_register(struct dax_device_driver *dax_drv,
 void dax_driver_unregister(struct dax_device_driver *dax_drv);
 void kill_dev_dax(struct dev_dax *dev_dax);
 
-#if IS_ENABLED(CONFIG_DEV_DAX_PMEM_COMPAT)
-int dev_dax_probe(struct dev_dax *dev_dax);
-#endif
-
 /*
  * While run_dax() is potentially a generic operation that could be
  * defined in include/linux/dax.h we don't want to grow any users

drivers/dax/bus.h

@@ -433,11 +433,7 @@ int dev_dax_probe(struct dev_dax *dev_dax)
 	inode = dax_inode(dax_dev);
 	cdev = inode->i_cdev;
 	cdev_init(cdev, &dax_fops);
-	if (dev->class) {
-		/* for the CONFIG_DEV_DAX_PMEM_COMPAT case */
-		cdev->owner = dev->parent->driver->owner;
-	} else
-		cdev->owner = dev->driver->owner;
+	cdev->owner = dev->driver->owner;
 	cdev_set_parent(cdev, &dev->kobj);
 	rc = cdev_add(cdev, dev->devt, 1);
 	if (rc)

drivers/dax/device.c

@@ -3,11 +3,11 @@
 #include <linux/memremap.h>
 #include <linux/module.h>
 #include <linux/pfn_t.h>
-#include "../../nvdimm/pfn.h"
-#include "../../nvdimm/nd.h"
-#include "../bus.h"
+#include "../nvdimm/pfn.h"
+#include "../nvdimm/nd.h"
+#include "bus.h"
 
-struct dev_dax *__dax_pmem_probe(struct device *dev, enum dev_dax_subsys subsys)
+static struct dev_dax *__dax_pmem_probe(struct device *dev)
 {
 	struct range range;
 	int rc, id, region_id;
@@ -63,7 +63,6 @@ struct dev_dax *__dax_pmem_probe(struct device *dev, enum dev_dax_subsys subsys)
 		.dax_region = dax_region,
 		.id = id,
 		.pgmap = &pgmap,
-		.subsys = subsys,
 		.size = range_len(&range),
 	};
 	dev_dax = devm_create_dev_dax(&data);
@@ -73,7 +72,32 @@ struct dev_dax *__dax_pmem_probe(struct device *dev, enum dev_dax_subsys subsys)
 
 	return dev_dax;
 }
-EXPORT_SYMBOL_GPL(__dax_pmem_probe);
+
+static int dax_pmem_probe(struct device *dev)
+{
+	return PTR_ERR_OR_ZERO(__dax_pmem_probe(dev));
+}
+
+static struct nd_device_driver dax_pmem_driver = {
+	.probe = dax_pmem_probe,
+	.drv = {
+		.name = "dax_pmem",
+	},
+	.type = ND_DRIVER_DAX_PMEM,
+};
+
+static int __init dax_pmem_init(void)
+{
+	return nd_driver_register(&dax_pmem_driver);
+}
+module_init(dax_pmem_init);
+
+static void __exit dax_pmem_exit(void)
+{
+	driver_unregister(&dax_pmem_driver.drv);
+}
+module_exit(dax_pmem_exit);
 
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Intel Corporation");
+MODULE_ALIAS_ND_DEVICE(ND_DEVICE_DAX_PMEM);

drivers/dax/pmem/core.c renamed to drivers/dax/pmem.c

@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem.o
 obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem_core.o
-obj-$(CONFIG_DEV_DAX_PMEM_COMPAT) += dax_pmem_compat.o
 
 dax_pmem-y := pmem.o
 dax_pmem_core-y := core.o

drivers/dax/pmem/Makefile

@@ -7,34 +7,4 @@
 #include <linux/nd.h>
 #include "../bus.h"
 
-static int dax_pmem_probe(struct device *dev)
-{
-	return PTR_ERR_OR_ZERO(__dax_pmem_probe(dev, DEV_DAX_BUS));
-}
 
-static struct nd_device_driver dax_pmem_driver = {
-	.probe = dax_pmem_probe,
-	.drv = {
-		.name = "dax_pmem",
-	},
-	.type = ND_DRIVER_DAX_PMEM,
-};
-
-static int __init dax_pmem_init(void)
-{
-	return nd_driver_register(&dax_pmem_driver);
-}
-module_init(dax_pmem_init);
-
-static void __exit dax_pmem_exit(void)
-{
-	driver_unregister(&dax_pmem_driver.drv);
-}
-module_exit(dax_pmem_exit);
-
-MODULE_LICENSE("GPL v2");
-MODULE_AUTHOR("Intel Corporation");
-#if !IS_ENABLED(CONFIG_DEV_DAX_PMEM_COMPAT)
-/* For compat builds, don't load this module by default */
-MODULE_ALIAS_ND_DEVICE(ND_DEVICE_DAX_PMEM);
-#endif

drivers/dax/pmem/compat.c

@@ -35,8 +35,6 @@ obj-$(CONFIG_DAX) += dax.o
 endif
 obj-$(CONFIG_DEV_DAX) += device_dax.o
 obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem.o
-obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem_core.o
-obj-$(CONFIG_DEV_DAX_PMEM_COMPAT) += dax_pmem_compat.o
 
 nfit-y := $(ACPI_SRC)/core.o
 nfit-y += $(ACPI_SRC)/intel.o
@@ -67,12 +65,8 @@ device_dax-y += dax-dev.o
 device_dax-y += device_dax_test.o
 device_dax-y += config_check.o
 
-dax_pmem-y := $(DAX_SRC)/pmem/pmem.o
+dax_pmem-y := $(DAX_SRC)/pmem.o
 dax_pmem-y += dax_pmem_test.o
-dax_pmem_core-y := $(DAX_SRC)/pmem/core.o
-dax_pmem_core-y += dax_pmem_core_test.o
-dax_pmem_compat-y := $(DAX_SRC)/pmem/compat.o
-dax_pmem_compat-y += dax_pmem_compat_test.o
 dax_pmem-y += config_check.o
 
 libnvdimm-y := $(NVDIMM_SRC)/core.o

drivers/dax/pmem/pmem.c

@@ -1054,10 +1054,6 @@ static __init int ndtest_init(void)
 	libnvdimm_test();
 	device_dax_test();
 	dax_pmem_test();
-	dax_pmem_core_test();
-#ifdef CONFIG_DEV_DAX_PMEM_COMPAT
-	dax_pmem_compat_test();
-#endif
 
 	nfit_test_setup(ndtest_resource_lookup, NULL);
 

tools/testing/nvdimm/Kbuild

@@ -3300,10 +3300,6 @@ static __init int nfit_test_init(void)
 	acpi_nfit_test();
 	device_dax_test();
 	dax_pmem_test();
-	dax_pmem_core_test();
-#ifdef CONFIG_DEV_DAX_PMEM_COMPAT
-	dax_pmem_compat_test();
-#endif
 
 	nfit_test_setup(nfit_test_lookup, nfit_test_evaluate_dsm);