[PATCH v3] mm/hmm/test: use char dev with struct device to get device node

[mpenttil]

From: Mika Penttilä <mpenttil@xxxxxxxxxx>

HMM selftests use an in-kernel pseudo device to emulate device private
memory. The pseudo device registers a major device range for two pseudo
device instances. User space has a script that reads /proc/devices in
order to find the assigned major number, and sends that to mknod(1),
once for each node.

This duplicates a fair amount of boilerplate that misc device can do
instead.

Change this to use misc device, which makes the device node names appear
for us. This also enables udev-like processing if desired.

Delete the /proc/devices parsing from the user-space test script, now
that it is unnecessary.

Signed-off-by: Mika Penttilä <mpenttil@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
---
v3:
        - use cdev_device_add() instead of miscdevice
v2:
        - Cleanups per review comments from John Hubbard
        - Added Tested-by and Ccs

 lib/test_hmm.c                         | 25 ++++++++++++++++++-------
 tools/testing/selftests/vm/test_hmm.sh |  6 ------
 2 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 767538089a62..d247e9c0fe94 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -29,11 +29,17 @@
 
 #include "test_hmm_uapi.h"
 
-#define DMIRROR_NDEVICES		2
 #define DMIRROR_RANGE_FAULT_TIMEOUT	1000
 #define DEVMEM_CHUNK_SIZE		(256 * 1024 * 1024U)
 #define DEVMEM_CHUNKS_RESERVE		16
 
+static const char *dmirror_device_names[] = {
+	"hmm_dmirror0",
+	"hmm_dmirror1"
+};
+
+#define DMIRROR_NDEVICES ARRAY_SIZE(dmirror_device_names)
+
 static const struct dev_pagemap_ops dmirror_devmem_ops;
 static const struct mmu_interval_notifier_ops dmirror_min_ops;
 static dev_t dmirror_dev;
@@ -74,7 +80,7 @@ struct dmirror {
  * ZONE_DEVICE pages for migration and simulating device memory.
  */
 struct dmirror_chunk {
-	struct dev_pagemap	pagemap;
+	struct dev_pagemap      pagemap;
 	struct dmirror_device	*mdevice;
 };
 
@@ -82,8 +88,9 @@ struct dmirror_chunk {
  * Per device data.
  */
 struct dmirror_device {
-	struct cdev		cdevice;
-	struct hmm_devmem	*devmem;
+	struct cdev             cdevice;
+	struct device           device;
+	struct hmm_devmem       *devmem;
 
 	unsigned int		devmem_capacity;
 	unsigned int		devmem_count;
@@ -132,7 +139,7 @@ static int dmirror_fops_open(struct inode *inode, struct file *filp)
 	xa_init(&dmirror->pt);
 
 	ret = mmu_interval_notifier_insert(&dmirror->notifier, current->mm,
-				0, ULONG_MAX & PAGE_MASK, &dmirror_min_ops);
+					0, ULONG_MAX & PAGE_MASK, &dmirror_min_ops);
 	if (ret) {
 		kfree(dmirror);
 		return ret;
@@ -1225,7 +1232,11 @@ static int dmirror_device_init(struct dmirror_device *mdevice, int id)
 
 	cdev_init(&mdevice->cdevice, &dmirror_fops);
 	mdevice->cdevice.owner = THIS_MODULE;
-	ret = cdev_add(&mdevice->cdevice, dev, 1);
+	device_initialize(&mdevice->device);
+	dev_set_name(&mdevice->device, "%s", dmirror_device_names[id]);
+	mdevice->device.devt = dev;
+
+	ret = cdev_device_add(&mdevice->cdevice, &mdevice->device);
 	if (ret)
 		return ret;
 
@@ -1252,7 +1263,7 @@ static void dmirror_device_remove(struct dmirror_device *mdevice)
 		kfree(mdevice->devmem_chunks);
 	}
 
-	cdev_del(&mdevice->cdevice);
+	cdev_device_del(&mdevice->cdevice, &mdevice->device);
 }
 
 static int __init hmm_dmirror_init(void)
diff --git a/tools/testing/selftests/vm/test_hmm.sh b/tools/testing/selftests/vm/test_hmm.sh
index 0647b525a625..69f5889f8575 100755
--- a/tools/testing/selftests/vm/test_hmm.sh
+++ b/tools/testing/selftests/vm/test_hmm.sh
@@ -41,17 +41,11 @@ check_test_requirements()
 load_driver()
 {
 	modprobe $DRIVER > /dev/null 2>&1
-	if [ $? == 0 ]; then
-		major=$(awk "\$2==\"HMM_DMIRROR\" {print \$1}" /proc/devices)
-		mknod /dev/hmm_dmirror0 c $major 0
-		mknod /dev/hmm_dmirror1 c $major 1
-	fi
 }
 
 unload_driver()
 {
 	modprobe -r $DRIVER > /dev/null 2>&1
-	rm -f /dev/hmm_dmirror?
 }
 
 run_smoke()
-- 
2.17.1