mm/hmm/test: use char dev with struct device to get device node

HMM selftests use an in-kernel pseudo device to emulate device memory. 
The pseudo device registers a major device range for two or four 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.

Change this to properly use cdev and struct device APIs.

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

Also, delete an unused field in struct dmirror_device: devmem.

Link: https://lkml.kernel.org/r/20220826050631.25771-1-mpenttil@redhat.comSigned-off-by: Mika Penttilä <mpenttil@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/test_hmm.c

@@ -107,8 +107,8 @@ struct dmirror_chunk {
  */
 struct dmirror_device {
 	struct cdev		cdevice;
-	struct hmm_devmem	*devmem;
 	unsigned int            zone_device_type;
+	struct device		device;
 
 	unsigned int		devmem_capacity;
 	unsigned int		devmem_count;
@@ -1390,7 +1390,14 @@ 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);
+	mdevice->device.devt = dev;
+
+	ret = dev_set_name(&mdevice->device, "hmm_dmirror%u", id);
+	if (ret)
+		return ret;
+
+	ret = cdev_device_add(&mdevice->cdevice, &mdevice->device);
 	if (ret)
 		return ret;
 
@@ -1416,7 +1423,7 @@ 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)

tools/testing/selftests/vm/test_hmm.sh

@@ -52,21 +52,11 @@ load_driver()
 			usage
 		fi
 	fi
-	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
-		if [ $# -eq 2 ]; then
-			mknod /dev/hmm_dmirror2 c $major 2
-			mknod /dev/hmm_dmirror3 c $major 3
-		fi
-	fi
 }
 
 unload_driver()
 {
 	modprobe -r $DRIVER > /dev/null 2>&1
-	rm -f /dev/hmm_dmirror?
 }
 
 run_smoke()